diff --git a/scenarios/http/js/README.md b/scenarios/http/js/README.md
index d4c93cbad..99410b9b4 100644
--- a/scenarios/http/js/README.md
+++ b/scenarios/http/js/README.md
@@ -7,6 +7,8 @@ other language.
 ```text
 express/scenarios/                    what the server does, no OTel
 express/opentelemetry-express/        server.js, server/
+fetch/scenarios/                      what the browser Fetch client does, no OTel
+fetch/opentelemetry-fetch/            browser.js, client/
 http/scenarios/                       built-in client and server, no OTel
 http/opentelemetry-http/              client.js, server.js, client/, server/
 undici/scenarios/                     what the client does, no OTel
@@ -56,6 +58,24 @@ undici does not go through Node's `http` module, so its client spans come from
 `undici.request`, which reports every status rather than throwing on 4xx and
 5xx: the contract's failing statuses are traffic to be measured like any other.
 
+## Fetch
+
+Fetch is a browser API, so its scenario opens a headless browser through the
+shared browser runner. The runner serves the bundled browser workload, reserves
+only its own exporter and script endpoints, and proxies every contract request
+to the mock server unchanged. Browser spans therefore retain the contract's
+exact path and query string. Its telemetry bridge accepts the browser's
+OTLP/HTTP protobuf exports and forwards them to the runner's OTLP/gRPC
+collector; the exporter endpoint is ignored by Fetch instrumentation.
+
+The browser runner first launches an installed Google Chrome and falls back to
+Playwright-managed Chromium. Install that fallback once in the build root when
+Chrome is unavailable:
+
+```sh
+npm exec playwright install chromium
+```
+
 ## Running one
 
 Use Node 22.19.0 or newer. The lockfile pins `undici@8.10.0`, which requires
@@ -65,6 +85,7 @@ that version.
 pip install -e tools/runner -e tools/http/runner -e tools/http/mock-server \
   -e tools/http/test-client/python -e tools/js
 otel-conformance scenarios/http/js/express/opentelemetry-express/server
+otel-conformance scenarios/http/js/fetch/opentelemetry-fetch/client
 otel-conformance scenarios/http/js/http/opentelemetry-http/client
 otel-conformance scenarios/http/js/http/opentelemetry-http/server
 otel-conformance scenarios/http/js/undici/opentelemetry-undici/client
diff --git a/scenarios/http/js/fetch/opentelemetry-fetch/browser.js b/scenarios/http/js/fetch/opentelemetry-fetch/browser.js
new file mode 100644
index 000000000..45ff1a42e
--- /dev/null
+++ b/scenarios/http/js/fetch/opentelemetry-fetch/browser.js
@@ -0,0 +1,87 @@
+// Copyright The OpenTelemetry Authors
+// SPDX-License-Identifier: Apache-2.0
+
+"use strict";
+
+const {
+  OTLPTraceExporter,
+} = require("@opentelemetry/exporter-trace-otlp-proto");
+const { registerInstrumentations } = require("@opentelemetry/instrumentation");
+const {
+  FetchInstrumentation,
+} = require("@opentelemetry/instrumentation-fetch");
+const {
+  SimpleSpanProcessor,
+  WebTracerProvider,
+} = require("@opentelemetry/sdk-trace-web");
+const { drive } = require("@otel-conformance/fetch-scenarios");
+
+/** Resolves once exactly `expected` Fetch spans have reached the exporter. */
+function trackingExporter(exporter, expected) {
+  let exported = 0;
+  let resolve;
+  let reject;
+  const complete = new Promise((onResolve, onReject) => {
+    resolve = onResolve;
+    reject = onReject;
+  });
+  return {
+    export(spans, callback) {
+      exporter.export(spans, (result) => {
+        callback(result);
+        if (result.code !== 0) {
+          reject(result.error || new Error("OTLP export failed"));
+          return;
+        }
+        exported += spans.length;
+        if (exported === expected) {
+          resolve();
+        } else if (exported > expected) {
+          reject(new Error(`exported ${exported} spans, expected ${expected}`));
+        }
+      });
+    },
+    forceFlush() {
+      return exporter.forceFlush();
+    },
+    shutdown() {
+      return exporter.shutdown();
+    },
+    waitForExpectedSpans() {
+      return complete;
+    },
+  };
+}
+
+async function run() {
+  const { baseUrl, exchanges, traceExporterUrl } = window.__otelConformance;
+  const exporter = trackingExporter(
+    new OTLPTraceExporter({ url: traceExporterUrl }),
+    exchanges.filter((exchange) => !exchange.readiness).length,
+  );
+  const provider = new WebTracerProvider({
+    spanProcessors: [new SimpleSpanProcessor(exporter)],
+  });
+  provider.register();
+  registerInstrumentations({
+    tracerProvider: provider,
+    instrumentations: [
+      new FetchInstrumentation({ ignoreUrls: [traceExporterUrl] }),
+    ],
+  });
+  await drive(baseUrl, exchanges);
+  await exporter.waitForExpectedSpans();
+  await provider.forceFlush();
+}
+
+run().then(
+  () => {
+    window.__otelConformanceResult = { ok: true };
+  },
+  (error) => {
+    window.__otelConformanceResult = {
+      ok: false,
+      error: String(error.stack || error),
+    };
+  },
+);
diff --git a/scenarios/http/js/fetch/opentelemetry-fetch/client.js b/scenarios/http/js/fetch/opentelemetry-fetch/client.js
new file mode 100644
index 000000000..a9a34a3d5
--- /dev/null
+++ b/scenarios/http/js/fetch/opentelemetry-fetch/client.js
@@ -0,0 +1,17 @@
+// Copyright The OpenTelemetry Authors
+// SPDX-License-Identifier: Apache-2.0
+
+"use strict";
+
+const path = require("node:path");
+
+const { runBrowserScenario } = require("@otel-conformance/browser-runner");
+const { scenarioRequest } = require("@otel-conformance/http-test-client");
+
+runBrowserScenario({
+  entrypoint: path.join(__dirname, "browser.js"),
+  exchanges: [scenarioRequest()],
+}).catch((error) => {
+  console.error(error);
+  process.exitCode = 1;
+});
diff --git a/scenarios/http/js/fetch/opentelemetry-fetch/client/conformance.yaml b/scenarios/http/js/fetch/opentelemetry-fetch/client/conformance.yaml
new file mode 100644
index 000000000..46debdc3c
--- /dev/null
+++ b/scenarios/http/js/fetch/opentelemetry-fetch/client/conformance.yaml
@@ -0,0 +1,15 @@
+# Copyright The OpenTelemetry Authors
+# SPDX-License-Identifier: Apache-2.0
+
+runner: http-conformance
+instrumented_library: fetch
+instrumentation_library: "@opentelemetry/instrumentation-fetch"
+
+setup: otel-conformance-js install
+
+server:
+  run: http-mock-server --port ${PORT}
+
+scenarios:
+  client:
+    run: node ../client.js
diff --git a/scenarios/http/js/fetch/opentelemetry-fetch/client/data.json b/scenarios/http/js/fetch/opentelemetry-fetch/client/data.json
new file mode 100644
index 000000000..a3a987ad3
--- /dev/null
+++ b/scenarios/http/js/fetch/opentelemetry-fetch/client/data.json
@@ -0,0 +1,53 @@
+{
+  "spans": {
+    "http.client": [
+      "error.type",
+      "http.request.method",
+      "http.response.status_code",
+      "server.address",
+      "server.port",
+      "url.full"
+    ]
+  },
+  "events": {},
+  "metrics": {},
+  "entities": {
+    "service": {
+      "identity": [
+        "service.name"
+      ],
+      "description": []
+    },
+    "telemetry.sdk": {
+      "identity": [
+        "telemetry.sdk.language",
+        "telemetry.sdk.name"
+      ],
+      "description": [
+        "telemetry.sdk.version"
+      ]
+    }
+  },
+  "findings": [
+    {
+      "id": "recommended_attribute_not_present",
+      "message": "Span 'GET' is missing recommended attribute 'network.protocol.version'",
+      "signal_type": "span",
+      "signal_name": "GET",
+      "context": {
+        "attribute_key": "network.protocol.version",
+        "kind": "client"
+      }
+    },
+    {
+      "id": "recommended_attribute_not_present",
+      "message": "Span 'POST' is missing recommended attribute 'network.protocol.version'",
+      "signal_type": "span",
+      "signal_name": "POST",
+      "context": {
+        "attribute_key": "network.protocol.version",
+        "kind": "client"
+      }
+    }
+  ]
+}
diff --git a/scenarios/http/js/fetch/opentelemetry-fetch/package.json b/scenarios/http/js/fetch/opentelemetry-fetch/package.json
new file mode 100644
index 000000000..2357ebf40
--- /dev/null
+++ b/scenarios/http/js/fetch/opentelemetry-fetch/package.json
@@ -0,0 +1,16 @@
+{
+  "name": "@otel-conformance/fetch-opentelemetry-fetch",
+  "version": "0.1.0",
+  "private": true,
+  "description": "Browser Fetch measured through @opentelemetry/instrumentation-fetch.",
+  "license": "Apache-2.0",
+  "dependencies": {
+    "@opentelemetry/exporter-trace-otlp-proto": "0.221.0",
+    "@opentelemetry/instrumentation": "0.221.0",
+    "@opentelemetry/instrumentation-fetch": "0.221.0",
+    "@opentelemetry/sdk-trace-web": "2.10.0",
+    "@otel-conformance/browser-runner": "file:../../../../../tools/js/browser-runner",
+    "@otel-conformance/fetch-scenarios": "*",
+    "@otel-conformance/http-test-client": "file:../../../../../tools/http/test-client/js"
+  }
+}
diff --git a/scenarios/http/js/fetch/opentelemetry-fetch/test/client.test.js b/scenarios/http/js/fetch/opentelemetry-fetch/test/client.test.js
new file mode 100644
index 000000000..06a1460f5
--- /dev/null
+++ b/scenarios/http/js/fetch/opentelemetry-fetch/test/client.test.js
@@ -0,0 +1,219 @@
+// Copyright The OpenTelemetry Authors
+// SPDX-License-Identifier: Apache-2.0
+
+"use strict";
+
+const assert = require("node:assert/strict");
+const { spawn } = require("node:child_process");
+const http = require("node:http");
+const path = require("node:path");
+const test = require("node:test");
+const { URL } = require("node:url");
+
+const grpc = require("@grpc/grpc-js");
+const { respond } = require("@otel-conformance/http-test-client");
+
+const TRACE_EXPORT_PATH =
+  "/opentelemetry.proto.collector.trace.v1.TraceService/Export";
+
+const service = {
+  export: {
+    path: TRACE_EXPORT_PATH,
+    requestStream: false,
+    responseStream: false,
+    requestSerialize: (value) => value,
+    requestDeserialize: (value) => value,
+    responseSerialize: (value) => value,
+    responseDeserialize: (value) => value,
+  },
+};
+
+function listen(server) {
+  return new Promise((resolve) => server.listen(0, "127.0.0.1", resolve));
+}
+
+function close(server) {
+  server.closeAllConnections?.();
+  return new Promise((resolve) => server.close(resolve));
+}
+
+function bind(server) {
+  return new Promise((resolve, reject) => {
+    server.bindAsync(
+      "127.0.0.1:0",
+      grpc.ServerCredentials.createInsecure(),
+      (error, port) => (error ? reject(error) : resolve(port)),
+    );
+  });
+}
+
+function run(environment) {
+  return new Promise((resolve, reject) => {
+    const child = spawn(process.execPath, ["client.js"], {
+      cwd: path.resolve(__dirname, ".."),
+      env: { ...process.env, ...environment },
+      stdio: "inherit",
+    });
+    child.once("error", reject);
+    child.once("exit", (code) =>
+      code === 0 ? resolve() : reject(new Error(`scenario exited ${code}`)),
+    );
+  });
+}
+
+function varint(buffer, offset) {
+  let value = 0;
+  let shift = 0;
+  for (;;) {
+    const byte = buffer[offset++];
+    value += (byte & 0x7f) * 2 ** shift;
+    if ((byte & 0x80) === 0) {
+      return { offset, value };
+    }
+    shift += 7;
+  }
+}
+
+function fields(buffer) {
+  const result = [];
+  let offset = 0;
+  while (offset < buffer.length) {
+    const key = varint(buffer, offset);
+    offset = key.offset;
+    const wireType = key.value & 7;
+    const number = key.value >> 3;
+    if (wireType === 0) {
+      const value = varint(buffer, offset);
+      result.push({ number, value: value.value, wireType });
+      offset = value.offset;
+      continue;
+    }
+    if (wireType === 2) {
+      const size = varint(buffer, offset);
+      offset = size.offset;
+      result.push({
+        number,
+        value: buffer.subarray(offset, offset + size.value),
+        wireType,
+      });
+      offset += size.value;
+      continue;
+    }
+    if (wireType === 1 || wireType === 5) {
+      const size = wireType === 1 ? 8 : 4;
+      result.push({
+        number,
+        value: buffer.subarray(offset, offset + size),
+        wireType,
+      });
+      offset += size;
+      continue;
+    }
+    throw new Error(`unsupported protobuf wire type ${wireType}`);
+  }
+  return result;
+}
+
+function first(fieldsList, number, wireType) {
+  return fieldsList.find(
+    (field) => field.number === number && field.wireType === wireType,
+  )?.value;
+}
+
+function all(fieldsList, number, wireType) {
+  return fieldsList
+    .filter((field) => field.number === number && field.wireType === wireType)
+    .map((field) => field.value);
+}
+
+function text(value) {
+  return value.toString("utf8");
+}
+
+function attribute(value) {
+  const keyValue = fields(value);
+  const key = text(first(keyValue, 1, 2));
+  const anyValue = fields(first(keyValue, 2, 2));
+  const raw = first(anyValue, 1, 2) ?? first(anyValue, 3, 0);
+  return [key, Buffer.isBuffer(raw) ? text(raw) : raw];
+}
+
+function decodeSpans(payload) {
+  return all(fields(payload), 1, 2).flatMap((resourceSpans) =>
+    all(fields(resourceSpans), 2, 2).flatMap((scopeSpans) =>
+      all(fields(scopeSpans), 2, 2).map((encoded) => {
+        const span = fields(encoded);
+        return {
+          attributes: new Map(all(span, 9, 2).map(attribute)),
+          kind: first(span, 6, 0),
+          name: text(first(span, 5, 2)),
+        };
+      }),
+    ),
+  );
+}
+
+test("measures only the selected browser Fetch request", async () => {
+  const mock = http.createServer(async (request, response) => {
+    const chunks = [];
+    for await (const chunk of request) {
+      chunks.push(chunk);
+    }
+    const body = chunks.length ? Buffer.concat(chunks).toString("utf8") : null;
+    const answer = respond(
+      request.method,
+      new URL(request.url, "http://unused").pathname,
+      body,
+    );
+    response.writeHead(answer.status, {
+      "content-type": "application/json",
+    });
+    response.end(answer.body);
+  });
+  await listen(mock);
+
+  const exports = [];
+  const collector = new grpc.Server();
+  collector.addService(service, {
+    export(call, callback) {
+      exports.push(call.request);
+      callback(null, Buffer.alloc(0));
+    },
+  });
+  const collectorPort = await bind(collector);
+  collector.start();
+
+  try {
+    await run({
+      MOCK_SERVER_URL: `http://127.0.0.1:${mock.address().port}`,
+      OTEL_CONFORMANCE_SCENARIO_INDEX: "2",
+      OTEL_EXPORTER_OTLP_ENDPOINT: `http://127.0.0.1:${collectorPort}`,
+    });
+  } finally {
+    await close(mock);
+    collector.forceShutdown();
+  }
+  const spans = exports.flatMap(decodeSpans);
+  assert.equal(spans.length, 1, "the exporter request must not create a span");
+  assert.deepEqual(
+    spans.map(({ attributes, kind, name }) => {
+      const url = new URL(attributes.get("url.full"));
+      return {
+        kind,
+        method: attributes.get("http.request.method"),
+        name,
+        path: `${url.pathname}${url.search}`,
+        status: attributes.get("http.response.status_code"),
+      };
+    }),
+    [
+      {
+        kind: 3,
+        method: "POST",
+        name: "POST",
+        path: "/items",
+        status: 201,
+      },
+    ],
+  );
+});
diff --git a/scenarios/http/js/fetch/scenarios/client.js b/scenarios/http/js/fetch/scenarios/client.js
new file mode 100644
index 000000000..57c749b87
--- /dev/null
+++ b/scenarios/http/js/fetch/scenarios/client.js
@@ -0,0 +1,41 @@
+// Copyright The OpenTelemetry Authors
+// SPDX-License-Identifier: Apache-2.0
+
+"use strict";
+
+const {
+  isJsonEqual,
+} = require("@otel-conformance/http-test-client/json-equal");
+
+/** Sends the shared exchanges with browser Fetch, without telemetry setup. */
+
+async function drive(baseUrl, exchanges) {
+  for (const exchange of exchanges) {
+    if (exchange.readiness) {
+      continue;
+    }
+    const response = await fetch(`${baseUrl}${exchange.path}`, {
+      method: exchange.method,
+      headers:
+        exchange.body === null ? {} : { "content-type": "application/json" },
+      body: exchange.body,
+    });
+    const body = await response.text();
+    if (response.status !== exchange.status) {
+      throw new Error(
+        `${exchange.method} ${exchange.path} answered ${response.status}, expected ${exchange.status}`,
+      );
+    }
+    const expected = exchange.responseBody.replace(
+      "${requestBody}",
+      () => exchange.body ?? "{}",
+    );
+    if (!isJsonEqual(JSON.parse(body), JSON.parse(expected))) {
+      throw new Error(
+        `${exchange.method} ${exchange.path} answered outside the contract`,
+      );
+    }
+  }
+}
+
+module.exports = { drive };
diff --git a/scenarios/http/js/fetch/scenarios/package.json b/scenarios/http/js/fetch/scenarios/package.json
new file mode 100644
index 000000000..4936fb604
--- /dev/null
+++ b/scenarios/http/js/fetch/scenarios/package.json
@@ -0,0 +1,11 @@
+{
+  "name": "@otel-conformance/fetch-scenarios",
+  "version": "0.1.0",
+  "private": true,
+  "description": "What the browser Fetch HTTP conformance scenario does, with no OpenTelemetry in it.",
+  "license": "Apache-2.0",
+  "main": "client.js",
+  "dependencies": {
+    "@otel-conformance/http-test-client": "0.1.0"
+  }
+}
diff --git a/scenarios/http/js/package-lock.json b/scenarios/http/js/package-lock.json
index 8c93fb3a5..02dd97199 100644
--- a/scenarios/http/js/package-lock.json
+++ b/scenarios/http/js/package-lock.json
@@ -10,6 +10,7 @@
       "license": "Apache-2.0",
       "workspaces": [
         "express/*",
+        "fetch/*",
         "http/*",
         "undici/*"
       ],
@@ -38,6 +39,192 @@
         "express": "5.3.0"
       }
     },
+    "fetch/opentelemetry-fetch": {
+      "name": "@otel-conformance/fetch-opentelemetry-fetch",
+      "version": "0.1.0",
+      "license": "Apache-2.0",
+      "dependencies": {
+        "@opentelemetry/exporter-trace-otlp-proto": "0.221.0",
+        "@opentelemetry/instrumentation": "0.221.0",
+        "@opentelemetry/instrumentation-fetch": "0.221.0",
+        "@opentelemetry/sdk-trace-web": "2.10.0",
+        "@otel-conformance/browser-runner": "file:../../../../../tools/js/browser-runner",
+        "@otel-conformance/fetch-scenarios": "*",
+        "@otel-conformance/http-test-client": "file:../../../../../tools/http/test-client/js"
+      }
+    },
+    "fetch/opentelemetry-fetch/node_modules/@opentelemetry/api-logs": {
+      "version": "0.221.0",
+      "resolved": "https://registry.npmjs.org/@opentelemetry/api-logs/-/api-logs-0.221.0.tgz",
+      "integrity": "sha512-OlanaW1vv7ufTqQ3/fPLI4arGt5ZoM+P8abOMki6uEYnpRazepSWDwDnnw+la7kE26SHVC18//SMccrDvLKOXQ==",
+      "license": "Apache-2.0",
+      "dependencies": {
+        "@opentelemetry/api": "^1.3.0"
+      },
+      "engines": {
+        "node": ">=8.0.0"
+      }
+    },
+    "fetch/opentelemetry-fetch/node_modules/@opentelemetry/core": {
+      "version": "2.10.0",
+      "resolved": "https://registry.npmjs.org/@opentelemetry/core/-/core-2.10.0.tgz",
+      "integrity": "sha512-/wNZ8twnEQQA4HoHu22+vcsdru6pWPWxW+7w+FlxT6Id7PE/WIbZmVKkte+PF72e0F2dnImFeHD2syyE1Mw6MQ==",
+      "license": "Apache-2.0",
+      "dependencies": {
+        "@opentelemetry/semantic-conventions": "^1.29.0"
+      },
+      "engines": {
+        "node": "^18.19.0 || >=20.6.0"
+      },
+      "peerDependencies": {
+        "@opentelemetry/api": ">=1.0.0 <1.10.0"
+      }
+    },
+    "fetch/opentelemetry-fetch/node_modules/@opentelemetry/exporter-trace-otlp-proto": {
+      "version": "0.221.0",
+      "resolved": "https://registry.npmjs.org/@opentelemetry/exporter-trace-otlp-proto/-/exporter-trace-otlp-proto-0.221.0.tgz",
+      "integrity": "sha512-Z9i2T7vgZbWe9rSLYxXVIbeW+XyzUq4rZanW3ZyVNwVDqCsh0EJKUgBWWQ0CZfeuUA+RQPzKgJQHMuWAUnKqXw==",
+      "license": "Apache-2.0",
+      "dependencies": {
+        "@opentelemetry/otlp-exporter-base": "0.221.0",
+        "@opentelemetry/otlp-transformer": "0.221.0",
+        "@opentelemetry/sdk-trace": "2.10.0"
+      },
+      "engines": {
+        "node": "^18.19.0 || >=20.6.0"
+      },
+      "peerDependencies": {
+        "@opentelemetry/api": "^1.3.0"
+      }
+    },
+    "fetch/opentelemetry-fetch/node_modules/@opentelemetry/instrumentation": {
+      "version": "0.221.0",
+      "resolved": "https://registry.npmjs.org/@opentelemetry/instrumentation/-/instrumentation-0.221.0.tgz",
+      "integrity": "sha512-cCk80Z/iRDf/5gfsKMB4f74LqVA5yKETB/9ojPzVW/6/f70iu89nJvGxsFCxx4XfSohaOofkU19kiYm84AiAlw==",
+      "license": "Apache-2.0",
+      "dependencies": {
+        "@opentelemetry/api-logs": "0.221.0",
+        "import-in-the-middle": "^3.0.0",
+        "require-in-the-middle": "^8.0.0"
+      },
+      "engines": {
+        "node": "^18.19.0 || >=20.6.0"
+      },
+      "peerDependencies": {
+        "@opentelemetry/api": "^1.3.0"
+      }
+    },
+    "fetch/opentelemetry-fetch/node_modules/@opentelemetry/otlp-exporter-base": {
+      "version": "0.221.0",
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     "http/opentelemetry-http": {
       "name": "@otel-conformance/node-http-opentelemetry-http",
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@@ -57,6 +244,422 @@
         "@otel-conformance/scenario-support": "file:../../../../../tools/js/scenario-support"
       }
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+        "win32"
+      ],
+      "engines": {
+        "node": ">=18"
+      }
+    },
+    "node_modules/@esbuild/win32-x64": {
+      "version": "0.28.2",
+      "resolved": "https://registry.npmjs.org/@esbuild/win32-x64/-/win32-x64-0.28.2.tgz",
+      "integrity": "sha512-5ebpxr3nWMzrL/rnUI755Jkuee0bHL/Gq0WTF9lvcpv73wAp5eu8MfBUgWK9bhWvZjj7yX8etf/8tI8Ney695g==",
+      "cpu": [
+        "x64"
+      ],
+      "license": "MIT",
+      "optional": true,
+      "os": [
+        "win32"
+      ],
+      "engines": {
+        "node": ">=18"
+      }
+    },
     "node_modules/@grpc/grpc-js": {
       "version": "1.14.5",
       "resolved": "https://registry.npmjs.org/@grpc/grpc-js/-/grpc-js-1.14.5.tgz",
@@ -389,6 +992,24 @@
         "@opentelemetry/api": "^1.3.0"
       }
     },
+    "node_modules/@opentelemetry/instrumentation-fetch": {
+      "version": "0.221.0",
+      "resolved": "https://registry.npmjs.org/@opentelemetry/instrumentation-fetch/-/instrumentation-fetch-0.221.0.tgz",
+      "integrity": "sha512-PPfEC0dIvhieidxtajOsbgFZ2RBUhCsk1ztHE6I5uinNc4JocL+UNRQY6iCBsckI0rjTwYvsYRYOJUjGyLhIug==",
+      "license": "Apache-2.0",
+      "dependencies": {
+        "@opentelemetry/core": "2.10.0",
+        "@opentelemetry/instrumentation": "0.221.0",
+        "@opentelemetry/sdk-trace-web": "2.10.0",
+        "@opentelemetry/semantic-conventions": "^1.29.0"
+      },
+      "engines": {
+        "node": "^18.19.0 || >=20.6.0"
+      },
+      "peerDependencies": {
+        "@opentelemetry/api": "^1.3.0"
+      }
+    },
     "node_modules/@opentelemetry/instrumentation-http": {
       "version": "0.223.0",
       "resolved": "https://registry.npmjs.org/@opentelemetry/instrumentation-http/-/instrumentation-http-0.223.0.tgz",
@@ -651,6 +1272,22 @@
         "@opentelemetry/api": ">=1.0.0 <1.10.0"
       }
     },
+    "node_modules/@opentelemetry/sdk-trace-web": {
+      "version": "2.10.0",
+      "resolved": "https://registry.npmjs.org/@opentelemetry/sdk-trace-web/-/sdk-trace-web-2.10.0.tgz",
+      "integrity": "sha512-6WqXdWSlBH0GNjDhv1gg6SLVtMtIBVhLaWqd1hiKSXS8meXXP13sVPQoYFHz1uVo0feUTUCdP9vMS54KflisAw==",
+      "license": "Apache-2.0",
+      "dependencies": {
+        "@opentelemetry/core": "2.10.0",
+        "@opentelemetry/sdk-trace-base": "2.10.0"
+      },
+      "engines": {
+        "node": "^18.19.0 || >=20.6.0"
+      },
+      "peerDependencies": {
+        "@opentelemetry/api": ">=1.0.0 <1.10.0"
+      }
+    },
     "node_modules/@opentelemetry/semantic-conventions": {
       "version": "1.43.0",
       "resolved": "https://registry.npmjs.org/@opentelemetry/semantic-conventions/-/semantic-conventions-1.43.0.tgz",
@@ -660,6 +1297,16 @@
         "node": ">=14"
       }
     },
+    "node_modules/@otel-conformance/browser-runner": {
+      "version": "0.1.0",
+      "resolved": "file:../../../tools/js/browser-runner",
+      "license": "Apache-2.0",
+      "dependencies": {
+        "@grpc/grpc-js": "1.14.4",
+        "@playwright/test": "1.62.1",
+        "esbuild": "0.28.2"
+      }
+    },
     "node_modules/@otel-conformance/express-opentelemetry-express": {
       "resolved": "express/opentelemetry-express",
       "link": true
@@ -668,6 +1315,14 @@
       "resolved": "express/scenarios",
       "link": true
     },
+    "node_modules/@otel-conformance/fetch-opentelemetry-fetch": {
+      "resolved": "fetch/opentelemetry-fetch",
+      "link": true
+    },
+    "node_modules/@otel-conformance/fetch-scenarios": {
+      "resolved": "fetch/scenarios",
+      "link": true
+    },
     "node_modules/@otel-conformance/http-test-client": {
       "version": "0.1.0",
       "resolved": "file:../../../tools/http/test-client/js",
@@ -706,6 +1361,21 @@
       "resolved": "undici/scenarios",
       "link": true
     },
+    "node_modules/@playwright/test": {
+      "version": "1.62.1",
+      "resolved": "https://registry.npmjs.org/@playwright/test/-/test-1.62.1.tgz",
+      "integrity": "sha512-DTcUc8qii+cpHvtOwggMtBRMjKZHXYWdw8syRYu2vtzuq4Wxphqq4NfCs5Zt44L6mA8rfDfj+PHnxFc/FeK6mQ==",
+      "license": "Apache-2.0",
+      "dependencies": {
+        "playwright": "1.62.1"
+      },
+      "bin": {
+        "playwright": "cli.js"
+      },
+      "engines": {
+        "node": ">=20"
+      }
+    },
     "node_modules/@protobufjs/aspromise": {
       "version": "1.1.2",
       "resolved": "https://registry.npmjs.org/@protobufjs/aspromise/-/aspromise-1.1.2.tgz",
@@ -1050,6 +1720,47 @@
         "node": ">= 0.4"
       }
     },
+    "node_modules/esbuild": {
+      "version": "0.28.2",
+      "resolved": "https://registry.npmjs.org/esbuild/-/esbuild-0.28.2.tgz",
+      "integrity": "sha512-HKVLS8dvII+xoKW9kmqxbRKrnWEXfJJr/FZhhJmiqIB0e053QNYFqOBouTMO/k5sID4MvCiUCvv8b9M4h32wIA==",
+      "hasInstallScript": true,
+      "license": "MIT",
+      "bin": {
+        "esbuild": "bin/esbuild"
+      },
+      "engines": {
+        "node": ">=18"
+      },
+      "optionalDependencies": {
+        "@esbuild/aix-ppc64": "0.28.2",
+        "@esbuild/android-arm": "0.28.2",
+        "@esbuild/android-arm64": "0.28.2",
+        "@esbuild/android-x64": "0.28.2",
+        "@esbuild/darwin-arm64": "0.28.2",
+        "@esbuild/darwin-x64": "0.28.2",
+        "@esbuild/freebsd-arm64": "0.28.2",
+        "@esbuild/freebsd-x64": "0.28.2",
+        "@esbuild/linux-arm": "0.28.2",
+        "@esbuild/linux-arm64": "0.28.2",
+        "@esbuild/linux-ia32": "0.28.2",
+        "@esbuild/linux-loong64": "0.28.2",
+        "@esbuild/linux-mips64el": "0.28.2",
+        "@esbuild/linux-ppc64": "0.28.2",
+        "@esbuild/linux-riscv64": "0.28.2",
+        "@esbuild/linux-s390x": "0.28.2",
+        "@esbuild/linux-x64": "0.28.2",
+        "@esbuild/netbsd-arm64": "0.28.2",
+        "@esbuild/netbsd-x64": "0.28.2",
+        "@esbuild/openbsd-arm64": "0.28.2",
+        "@esbuild/openbsd-x64": "0.28.2",
+        "@esbuild/openharmony-arm64": "0.28.2",
+        "@esbuild/sunos-x64": "0.28.2",
+        "@esbuild/win32-arm64": "0.28.2",
+        "@esbuild/win32-ia32": "0.28.2",
+        "@esbuild/win32-x64": "0.28.2"
+      }
+    },
     "node_modules/escalade": {
       "version": "3.2.0",
       "resolved": "https://registry.npmjs.org/escalade/-/escalade-3.2.0.tgz",
@@ -1162,6 +1873,20 @@
         "node": ">= 0.8"
       }
     },
+    "node_modules/fsevents": {
+      "version": "2.3.2",
+      "resolved": "https://registry.npmjs.org/fsevents/-/fsevents-2.3.2.tgz",
+      "integrity": "sha512-xiqMQR4xAeHTuB9uWm+fFRcIOgKBMiOBP+eXiyT7jsgVCq1bkVygt00oASowB7EdtpOHaaPgKt812P9ab+DDKA==",
+      "hasInstallScript": true,
+      "license": "MIT",
+      "optional": true,
+      "os": [
+        "darwin"
+      ],
+      "engines": {
+        "node": "^8.16.0 || ^10.6.0 || >=11.0.0"
+      }
+    },
     "node_modules/function-bind": {
       "version": "1.1.2",
       "resolved": "https://registry.npmjs.org/function-bind/-/function-bind-1.1.2.tgz",
@@ -1484,6 +2209,36 @@
         "url": "https://opencollective.com/express"
       }
     },
+    "node_modules/playwright": {
+      "version": "1.62.1",
+      "resolved": "https://registry.npmjs.org/playwright/-/playwright-1.62.1.tgz",
+      "integrity": "sha512-0M+L3LAD8/nm554LOla9Ayx0j0tmFZ0FBcoQ7F1VuVHpM/XpiC8RcDzBQB8W5+hA8L22THxELzeF+2WcUzvcLg==",
+      "license": "Apache-2.0",
+      "dependencies": {
+        "playwright-core": "1.62.1"
+      },
+      "bin": {
+        "playwright": "cli.js"
+      },
+      "engines": {
+        "node": ">=20"
+      },
+      "optionalDependencies": {
+        "fsevents": "2.3.2"
+      }
+    },
+    "node_modules/playwright-core": {
+      "version": "1.62.1",
+      "resolved": "https://registry.npmjs.org/playwright-core/-/playwright-core-1.62.1.tgz",
+      "integrity": "sha512-wPYSwEBJY9GHraISXqyqtx0na0LpO3XEX7jNDhntbex7tzUS7kLnZsOlFruFJB4Hi/rhDMjXGqHewDZ68nYZVw==",
+      "license": "Apache-2.0",
+      "bin": {
+        "playwright-core": "cli.js"
+      },
+      "engines": {
+        "node": ">=20"
+      }
+    },
     "node_modules/prettier": {
       "version": "3.9.10",
       "resolved": "https://registry.npmjs.org/prettier/-/prettier-3.9.10.tgz",
diff --git a/scenarios/http/js/package.json b/scenarios/http/js/package.json
index 069fece57..4fab4dbce 100644
--- a/scenarios/http/js/package.json
+++ b/scenarios/http/js/package.json
@@ -6,11 +6,12 @@
   "license": "Apache-2.0",
   "workspaces": [
     "express/*",
+    "fetch/*",
     "http/*",
     "undici/*"
   ],
   "scripts": {
-    "test": "npm ci --ignore-scripts --prefix ../../../tools/http/test-client/js && npm --prefix ../../../tools/http/test-client/js test && npm --prefix ../../../tools/js/scenario-sdk test",
+    "test": "npm ci --ignore-scripts --prefix ../../../tools/http/test-client/js && npm --prefix ../../../tools/http/test-client/js test && npm --prefix ../../../tools/js/scenario-sdk test && node node_modules/@otel-conformance/browser-runner/test/index.test.js && node fetch/opentelemetry-fetch/test/client.test.js",
     "format": "prettier --write . ../../../tools/js ../../../tools/http/test-client/js",
     "format:check": "prettier --check . ../../../tools/js ../../../tools/http/test-client/js"
   },
diff --git a/tools/http/test-client/js/README.md b/tools/http/test-client/js/README.md
index 3688675ee..1ab9d877d 100644
--- a/tools/http/test-client/js/README.md
+++ b/tools/http/test-client/js/README.md
@@ -1,12 +1,14 @@
-# HTTP conformance test client for Node
+# HTTP conformance test client for JavaScript
 
-The two halves of [the contract](../README.md) a Node scenario needs: answering
-a concrete request, and sending the measured ones.
+Shared [contract](../README.md) support for Node and browser scenarios. Node
+scenarios use the request sender and server response helpers; browser scenarios
+use the order-independent JSON comparison through the `json-equal` export.
 
 ```text
 src/contract.js         reads contract.yaml
 src/server-workload.js  answers one concrete request
-src/client-workload.js  sends one selected request
+src/client-workload.js  sends and checks one selected request
+src/json-equal.js       compares parsed JSON without object key ordering
 ```
 
 The only dependency is the YAML parser used before the measured request.
diff --git a/tools/http/test-client/js/package.json b/tools/http/test-client/js/package.json
index 0b8deb33d..6f1c160f4 100644
--- a/tools/http/test-client/js/package.json
+++ b/tools/http/test-client/js/package.json
@@ -2,9 +2,13 @@
   "name": "@otel-conformance/http-test-client",
   "version": "0.1.0",
   "private": true,
-  "description": "The HTTP conformance exchanges a Node scenario answers or sends.",
+  "description": "Shared HTTP conformance contract support for JavaScript scenarios.",
   "license": "Apache-2.0",
   "main": "src/index.js",
+  "exports": {
+    ".": "./src/index.js",
+    "./json-equal": "./src/json-equal.js"
+  },
   "files": [
     "src"
   ],
diff --git a/tools/http/test-client/js/src/client-workload.js b/tools/http/test-client/js/src/client-workload.js
index 072a6ca68..9d2858498 100644
--- a/tools/http/test-client/js/src/client-workload.js
+++ b/tools/http/test-client/js/src/client-workload.js
@@ -14,7 +14,8 @@
  * The shared telemetry contract checks what these requests emit.
  */
 
-const { scenarioRequest } = require("./contract");
+const { renderResponseBody, scenarioRequest } = require("./contract");
+const { isJsonEqual } = require("./json-equal");
 
 /**
  * Sends the runner-selected contract request at `baseUrl` through `send`.
@@ -40,6 +41,29 @@ async function drive(baseUrl, send) {
     `${exchange.method} ${exchange.path} -> ${response.status} ` +
       `${abbreviate(response.body)}`,
   );
+  verify(exchange, response);
+}
+
+/** Checks one answer against the exchange that describes it. */
+function verify(exchange, response) {
+  const where = `${exchange.method} ${exchange.path}`;
+  if (response.status !== exchange.status) {
+    throw new Error(
+      `${where} answered ${response.status}, but the contract's request ` +
+        `answers ${exchange.status}`,
+    );
+  }
+
+  // Parsed, not compared as text: whitespace and key order are a language's
+  // choice of JSON writer, and neither is part of the contract.
+  const expected = JSON.parse(renderResponseBody(exchange, exchange.body));
+  const actual = JSON.parse(response.body);
+  if (!isJsonEqual(actual, expected)) {
+    throw new Error(
+      `${where} answered ${JSON.stringify(actual)}, but the contract's ` +
+        `request answers ${JSON.stringify(expected)}`,
+    );
+  }
 }
 
 function abbreviate(value) {
diff --git a/tools/http/test-client/js/src/index.js b/tools/http/test-client/js/src/index.js
index 715be99d1..ec607656b 100644
--- a/tools/http/test-client/js/src/index.js
+++ b/tools/http/test-client/js/src/index.js
@@ -15,10 +15,12 @@
 
 const contract = require("./contract");
 const clientWorkload = require("./client-workload");
+const jsonEqual = require("./json-equal");
 const serverWorkload = require("./server-workload");
 
 module.exports = {
   ...contract,
   ...clientWorkload,
+  ...jsonEqual,
   ...serverWorkload,
 };
diff --git a/tools/http/test-client/js/src/json-equal.js b/tools/http/test-client/js/src/json-equal.js
new file mode 100644
index 000000000..2ed72a602
--- /dev/null
+++ b/tools/http/test-client/js/src/json-equal.js
@@ -0,0 +1,38 @@
+// Copyright The OpenTelemetry Authors
+// SPDX-License-Identifier: Apache-2.0
+
+"use strict";
+
+/** Compares parsed JSON values without assigning meaning to object key order. */
+function isJsonEqual(actual, expected) {
+  if (Object.is(actual, expected)) {
+    return true;
+  }
+  if (Array.isArray(actual) || Array.isArray(expected)) {
+    return (
+      Array.isArray(actual) &&
+      Array.isArray(expected) &&
+      actual.length === expected.length &&
+      actual.every((value, index) => isJsonEqual(value, expected[index]))
+    );
+  }
+  if (
+    actual === null ||
+    expected === null ||
+    typeof actual !== "object" ||
+    typeof expected !== "object"
+  ) {
+    return false;
+  }
+  const actualKeys = Object.keys(actual);
+  const expectedKeys = Object.keys(expected);
+  return (
+    actualKeys.length === expectedKeys.length &&
+    actualKeys.every(
+      (key) =>
+        Object.hasOwn(expected, key) && isJsonEqual(actual[key], expected[key]),
+    )
+  );
+}
+
+module.exports = { isJsonEqual };
diff --git a/tools/http/test-client/js/test/client-workload.test.js b/tools/http/test-client/js/test/client-workload.test.js
index 529d99014..a871a101f 100644
--- a/tools/http/test-client/js/test/client-workload.test.js
+++ b/tools/http/test-client/js/test/client-workload.test.js
@@ -50,12 +50,22 @@ describe("driving the contract", () => {
     ]);
   });
 
-  it("does not validate the response", async () => {
-    const previous = process.env[SCENARIO_INDEX_VARIABLE];
+  it("rejects a response outside the contract", async () => {
     await withScenarioIndex(0, () =>
-      drive(BASE_URL, () => ({ status: 599, body: "not json" })),
+      assert.rejects(
+        () => drive(BASE_URL, () => ({ status: 599, body: "not json" })),
+        /answered 599/,
+      ),
+    );
+  });
+
+  it("accepts equivalent JSON with a different object key order", async () => {
+    await withScenarioIndex(0, () =>
+      drive(BASE_URL, () => ({
+        status: 200,
+        body: '{"name":"Alice","id":123}',
+      })),
     );
-    assert.equal(process.env[SCENARIO_INDEX_VARIABLE], previous);
   });
 
   it("refuses a blank base URL before anything is sent", async () => {
diff --git a/tools/http/test-client/js/test/json-equal.test.js b/tools/http/test-client/js/test/json-equal.test.js
new file mode 100644
index 000000000..910aeb940
--- /dev/null
+++ b/tools/http/test-client/js/test/json-equal.test.js
@@ -0,0 +1,24 @@
+// Copyright The OpenTelemetry Authors
+// SPDX-License-Identifier: Apache-2.0
+
+"use strict";
+
+const assert = require("node:assert/strict");
+const test = require("node:test");
+
+const { isJsonEqual } = require("../src/json-equal");
+
+test("ignores object key order at every nesting level", () => {
+  assert.equal(
+    isJsonEqual(
+      { result: { name: "Ada", roles: [{ active: true, name: "admin" }] } },
+      { result: { roles: [{ name: "admin", active: true }], name: "Ada" } },
+    ),
+    true,
+  );
+});
+
+test("preserves array order and value types", () => {
+  assert.equal(isJsonEqual({ values: [1, 2] }, { values: [2, 1] }), false);
+  assert.equal(isJsonEqual({ value: 1 }, { value: "1" }), false);
+});
diff --git a/tools/js/README.md b/tools/js/README.md
index 60699ba5a..c494bfb19 100644
--- a/tools/js/README.md
+++ b/tools/js/README.md
@@ -8,6 +8,7 @@ itself, and the command that installs a Node build.
 scenarios/<domain>/js/      a domain's npm build root — workspaces and the lockfile
 tools/js/scenario-support/  what a scenario needs before any telemetry
 tools/js/scenario-sdk/      the SDK a library-instrumentation scenario owns
+tools/js/browser-runner/    browser launch and OTLP/HTTP-to-gRPC bridge
 tools/js/src/               `otel-conformance-js`, the launcher
 tools/js/tests/             the launcher's tests
 ```
diff --git a/tools/js/browser-runner/index.js b/tools/js/browser-runner/index.js
new file mode 100644
index 000000000..48392dcca
--- /dev/null
+++ b/tools/js/browser-runner/index.js
@@ -0,0 +1,219 @@
+// Copyright The OpenTelemetry Authors
+// SPDX-License-Identifier: Apache-2.0
+
+"use strict";
+
+/**
+ * Starts a browser workload and forwards its OTLP/HTTP protobuf exports to
+ * the conformance runner's OTLP/gRPC collector.
+ *
+ * A browser cannot speak OTLP/gRPC directly. The bridge gives its bundled
+ * page a same-origin OTLP/HTTP endpoint, then carries the protobuf request
+ * unchanged over gRPC. Every path except the bridge's own endpoints proxies
+ * unchanged to the runner's mock server, so Fetch observes the contract's
+ * exact paths without a cross-origin preflight.
+ */
+
+const http = require("node:http");
+const { URL } = require("node:url");
+
+const grpc = require("@grpc/grpc-js");
+const { chromium } = require("@playwright/test");
+const esbuild = require("esbuild");
+
+const TRACE_EXPORT_PATH =
+  "/opentelemetry.proto.collector.trace.v1.TraceService/Export";
+const BRIDGE_PATH = "/_otel-conformance";
+
+function requireEnv(name) {
+  const value = process.env[name];
+  if (!value) {
+    throw new Error(`required environment variable is missing: ${name}`);
+  }
+  return value;
+}
+
+function requireUrl(name) {
+  const value = requireEnv(name);
+  try {
+    const url = new URL(value);
+    if (!url.host) {
+      throw new Error("URL must include a host");
+    }
+    return url;
+  } catch (error) {
+    throw new Error(`required environment variable is not a URL: ${name}`, {
+      cause: error,
+    });
+  }
+}
+
+function grpcTraceClient(endpoint) {
+  const address = endpoint.host;
+  const TraceService = grpc.makeGenericClientConstructor(
+    {
+      export: {
+        path: TRACE_EXPORT_PATH,
+        requestStream: false,
+        responseStream: false,
+        requestSerialize: (value) => value,
+        requestDeserialize: (value) => value,
+        responseSerialize: (value) => value,
+        responseDeserialize: (value) => value,
+      },
+    },
+    "TraceService",
+  );
+  return new TraceService(address, grpc.credentials.createInsecure());
+}
+
+function forward(client, payload) {
+  return new Promise((resolve, reject) => {
+    client.export(payload, (error) => (error ? reject(error) : resolve()));
+  });
+}
+
+function read(request) {
+  return new Promise((resolve, reject) => {
+    const chunks = [];
+    request.on("data", (chunk) => chunks.push(chunk));
+    request.on("end", () => resolve(Buffer.concat(chunks)));
+    request.on("error", reject);
+  });
+}
+
+function proxy(request, response, mockServer) {
+  const target = new URL(request.url, mockServer);
+  const upstream = http.request(target, {
+    method: request.method,
+    headers: { ...request.headers, host: target.host },
+  });
+  upstream.on("response", (upstreamResponse) => {
+    response.writeHead(upstreamResponse.statusCode, upstreamResponse.headers);
+    upstreamResponse.pipe(response);
+  });
+  upstream.on("error", (error) => {
+    response.writeHead(502, { "content-type": "text/plain" });
+    response.end(error.message);
+  });
+  request.pipe(upstream);
+}
+
+function listen(server) {
+  return new Promise((resolve, reject) => {
+    server.once("error", reject);
+    server.listen(0, "127.0.0.1", () => {
+      server.off("error", reject);
+      resolve(server.address().port);
+    });
+  });
+}
+
+function close(server) {
+  server.closeAllConnections?.();
+  return new Promise((resolve, reject) =>
+    server.close((error) => (error ? reject(error) : resolve())),
+  );
+}
+
+/** Prefer a locally installed Chrome, then Playwright's managed Chromium. */
+async function launchBrowser(browserType = chromium) {
+  try {
+    return await browserType.launch({ channel: "chrome", headless: true });
+  } catch {
+    return browserType.launch({ headless: true });
+  }
+}
+
+async function bundle(entrypoint) {
+  const result = await esbuild.build({
+    bundle: true,
+    entryPoints: [entrypoint],
+    format: "iife",
+    platform: "browser",
+    target: "es2022",
+    write: false,
+  });
+  return result.outputFiles[0].text;
+}
+
+/** Runs one bundled browser workload against the shared HTTP contract. */
+async function runBrowserScenario({ entrypoint, exchanges }) {
+  const mockServer = requireUrl("MOCK_SERVER_URL");
+  const collectorEndpoint = requireUrl("OTEL_EXPORTER_OTLP_ENDPOINT");
+  const collector = grpcTraceClient(collectorEndpoint);
+  let server;
+  let browser;
+  try {
+    const script = await bundle(entrypoint);
+    let bridgeUrl;
+    server = http.createServer(async (request, response) => {
+      try {
+        if (request.method === "GET" && request.url === "/") {
+          response.writeHead(200, {
+            "content-type": "text/html; charset=utf-8",
+          });
+          response.end(
+            `<!doctype html><link rel="icon" href="data:,"><script src="${BRIDGE_PATH}/scenario.js"></script>`,
+          );
+          return;
+        }
+        if (
+          request.method === "GET" &&
+          request.url === `${BRIDGE_PATH}/scenario.js`
+        ) {
+          response.writeHead(200, {
+            "content-type": "text/javascript; charset=utf-8",
+          });
+          response.end(
+            `window.__otelConformance = ${JSON.stringify({
+              baseUrl: bridgeUrl,
+              traceExporterUrl: `${bridgeUrl}${BRIDGE_PATH}/v1/traces`,
+              exchanges,
+            })};\n${script}`,
+          );
+          return;
+        }
+        if (
+          request.method === "POST" &&
+          request.url === `${BRIDGE_PATH}/v1/traces`
+        ) {
+          await forward(collector, await read(request));
+          response.writeHead(200);
+          response.end();
+          return;
+        }
+        proxy(request, response, mockServer);
+      } catch (error) {
+        response.writeHead(500, { "content-type": "text/plain" });
+        response.end(error instanceof Error ? error.stack : String(error));
+      }
+    });
+    const port = await listen(server);
+    bridgeUrl = `http://127.0.0.1:${port}`;
+    browser = await launchBrowser();
+    const page = await browser.newPage();
+    await page.goto(bridgeUrl);
+    await page.waitForFunction(
+      () => window.__otelConformanceResult !== undefined,
+    );
+    const result = await page.evaluate(() => window.__otelConformanceResult);
+    if (!result.ok) {
+      throw new Error(result.error);
+    }
+  } finally {
+    try {
+      await browser?.close();
+    } finally {
+      try {
+        if (server?.listening) {
+          await close(server);
+        }
+      } finally {
+        collector.close();
+      }
+    }
+  }
+}
+
+module.exports = { launchBrowser, runBrowserScenario };
diff --git a/tools/js/browser-runner/package.json b/tools/js/browser-runner/package.json
new file mode 100644
index 000000000..638359daf
--- /dev/null
+++ b/tools/js/browser-runner/package.json
@@ -0,0 +1,16 @@
+{
+  "name": "@otel-conformance/browser-runner",
+  "version": "0.1.0",
+  "private": true,
+  "description": "Runs a bundled browser conformance workload and bridges its OTLP telemetry.",
+  "license": "Apache-2.0",
+  "main": "index.js",
+  "scripts": {
+    "test": "node test/index.test.js"
+  },
+  "dependencies": {
+    "@grpc/grpc-js": "1.14.4",
+    "@playwright/test": "1.62.1",
+    "esbuild": "0.28.2"
+  }
+}
diff --git a/tools/js/browser-runner/test/fixtures/browser.js b/tools/js/browser-runner/test/fixtures/browser.js
new file mode 100644
index 000000000..9dab02afb
--- /dev/null
+++ b/tools/js/browser-runner/test/fixtures/browser.js
@@ -0,0 +1,17 @@
+window
+  .fetch(`${window.__otelConformance.baseUrl}/example`)
+  .then(async (response) => {
+    if ((await response.text()) !== "contract response") {
+      throw new Error("the bridge did not proxy the contract response");
+    }
+    return window.fetch(window.__otelConformance.traceExporterUrl, {
+      method: "POST",
+      body: new Uint8Array([1, 2, 3]),
+    });
+  })
+  .then(() => {
+    window.__otelConformanceResult = { ok: true };
+  })
+  .catch((error) => {
+    window.__otelConformanceResult = { ok: false, error: String(error) };
+  });
diff --git a/tools/js/browser-runner/test/index.test.js b/tools/js/browser-runner/test/index.test.js
new file mode 100644
index 000000000..69b8272d4
--- /dev/null
+++ b/tools/js/browser-runner/test/index.test.js
@@ -0,0 +1,137 @@
+// Copyright The OpenTelemetry Authors
+// SPDX-License-Identifier: Apache-2.0
+
+"use strict";
+
+const assert = require("node:assert/strict");
+const http = require("node:http");
+const path = require("node:path");
+const test = require("node:test");
+
+const grpc = require("@grpc/grpc-js");
+
+const { launchBrowser, runBrowserScenario } = require("../index");
+
+const TRACE_EXPORT_PATH =
+  "/opentelemetry.proto.collector.trace.v1.TraceService/Export";
+
+const service = {
+  export: {
+    path: TRACE_EXPORT_PATH,
+    requestStream: false,
+    responseStream: false,
+    requestSerialize: (value) => value,
+    requestDeserialize: (value) => value,
+    responseSerialize: (value) => value,
+    responseDeserialize: (value) => value,
+  },
+};
+
+function listen(server) {
+  return new Promise((resolve) => server.listen(0, "127.0.0.1", resolve));
+}
+
+function close(server) {
+  server.closeAllConnections?.();
+  return new Promise((resolve) => server.close(resolve));
+}
+
+function bind(server) {
+  return new Promise((resolve, reject) => {
+    server.bindAsync(
+      "127.0.0.1:0",
+      grpc.ServerCredentials.createInsecure(),
+      (error, port) => (error ? reject(error) : resolve(port)),
+    );
+  });
+}
+
+test("falls back to Playwright's managed Chromium", async () => {
+  const launches = [];
+  const managed = { close() {} };
+  const browserType = {
+    async launch(options) {
+      launches.push(options);
+      if (options.channel === "chrome") {
+        throw new Error("Chrome is not installed");
+      }
+      return managed;
+    },
+  };
+
+  assert.equal(await launchBrowser(browserType), managed);
+  assert.deepEqual(launches, [
+    { channel: "chrome", headless: true },
+    { headless: true },
+  ]);
+});
+
+test("validates the mock URL before constructing a collector client", async () => {
+  const original = Object.getOwnPropertyDescriptor(
+    grpc,
+    "makeGenericClientConstructor",
+  );
+  let constructed = false;
+  const previous = {
+    mock: process.env.MOCK_SERVER_URL,
+    endpoint: process.env.OTEL_EXPORTER_OTLP_ENDPOINT,
+  };
+  Object.defineProperty(grpc, "makeGenericClientConstructor", {
+    configurable: true,
+    value: () => {
+      constructed = true;
+    },
+  });
+  process.env.MOCK_SERVER_URL = "not a URL";
+  process.env.OTEL_EXPORTER_OTLP_ENDPOINT = "http://127.0.0.1:4317";
+  try {
+    await assert.rejects(
+      runBrowserScenario({ entrypoint: "unused.js", exchanges: [] }),
+      /MOCK_SERVER_URL/,
+    );
+  } finally {
+    Object.defineProperty(grpc, "makeGenericClientConstructor", original);
+    process.env.MOCK_SERVER_URL = previous.mock;
+    process.env.OTEL_EXPORTER_OTLP_ENDPOINT = previous.endpoint;
+  }
+  assert.equal(constructed, false);
+});
+
+test("proxies contract traffic and forwards browser OTLP protobuf", async () => {
+  const mock = http.createServer((request, response) => {
+    assert.equal(request.url, "/example");
+    response.end("contract response");
+  });
+  await listen(mock);
+  const mockPort = mock.address().port;
+
+  let telemetry;
+  const collector = new grpc.Server();
+  collector.addService(service, {
+    export(call, callback) {
+      telemetry = call.request;
+      callback(null, Buffer.alloc(0));
+    },
+  });
+  const collectorPort = await bind(collector);
+  collector.start();
+
+  const previous = {
+    mock: process.env.MOCK_SERVER_URL,
+    endpoint: process.env.OTEL_EXPORTER_OTLP_ENDPOINT,
+  };
+  process.env.MOCK_SERVER_URL = `http://127.0.0.1:${mockPort}`;
+  process.env.OTEL_EXPORTER_OTLP_ENDPOINT = `http://127.0.0.1:${collectorPort}`;
+  try {
+    await runBrowserScenario({
+      entrypoint: path.join(__dirname, "fixtures", "browser.js"),
+      exchanges: [],
+    });
+  } finally {
+    process.env.MOCK_SERVER_URL = previous.mock;
+    process.env.OTEL_EXPORTER_OTLP_ENDPOINT = previous.endpoint;
+    await close(mock);
+    collector.forceShutdown();
+  }
+  assert.deepEqual(telemetry, Buffer.from([1, 2, 3]));
+});