diff --git a/.flake8 b/.flake8
new file mode 100644
index 0000000..af70a91
--- /dev/null
+++ b/.flake8
@@ -0,0 +1,7 @@
+[flake8]
+exclude=
+    tests/**,
+    conftest.py,
+    setup.py
+max-line-length=120
+ignore=E731,W503,E203,BLK100,B301
\ No newline at end of file
diff --git a/tests/conftest.py b/tests/conftest.py
new file mode 100644
index 0000000..7e4b9d3
--- /dev/null
+++ b/tests/conftest.py
@@ -0,0 +1,66 @@
+import datetime
+import json
+import os
+import collections
+
+import pytest
+
+
+class ValidationError(Exception):
+    pass
+
+
+@pytest.fixture
+def spec_validator():
+    with open(
+        os.path.join(os.path.dirname(__file__), "resources", "spec.json"), "r"
+    ) as fh:
+        spec = json.load(fh)
+
+    def validator(data_json):
+        """
+        Throws a ValidationError if anything doesn't match the spec.
+
+        Returns the original json (pass-through)
+        """
+        fields = spec["fields"]
+        data = json.loads(data_json, object_pairs_hook=collections.OrderedDict)
+        for k, v in fields.items():
+            if v.get("required"):
+                found = False
+                if k in data:
+                    found = True
+                elif "." in k:
+                    # Dotted keys could be nested, like ecs.version
+                    subkeys = k.split(".")
+                    subval = data
+                    for subkey in subkeys:
+                        subval = subval.get(subkey, {})
+                    if subval:
+                        found = True
+                if not found:
+                    raise ValidationError("Missing required key {}".format(k))
+            if k in data:
+                if v["type"] == "string" and not (
+                    isinstance(data[k], str) or isinstance(data[k], basestring)
+                ):
+                    raise ValidationError(
+                        "Value {0} for key {1} should be string, is {2}".format(
+                            data[k], k, type(data[k])
+                        )
+                    )
+                if v["type"] == "datetime":
+                    try:
+                        datetime.datetime.strptime(data[k], "%Y-%m-%dT%H:%M:%S.%fZ")
+                    except ValueError:
+                        raise ValidationError(
+                            "Value {0} for key {1} doesn't parse as an ISO datetime".format(
+                                data[k], k
+                            )
+                        )
+            if v.get("index") and list(data.keys())[v.get("index")] != k:
+                raise ValidationError("Key {0} is not at index {1}".format(k, index))
+
+        return data_json
+
+    return validator
diff --git a/tests/resources/spec.json b/tests/resources/spec.json
new file mode 100644
index 0000000..14cca2e
--- /dev/null
+++ b/tests/resources/spec.json
@@ -0,0 +1,139 @@
+{
+    "version": 1.0,
+    "url": "https://www.elastic.co/guide/en/ecs/current/index.html",
+    "ecs": {
+        "version": "1.x"
+    },
+    "fields": {
+        "@timestamp": {
+            "type": "datetime",
+            "required": true,
+            "index": 0,
+            "url": "https://www.elastic.co/guide/en/ecs/current/ecs-base.html"
+        },
+        "log.level": {
+            "type": "string",
+            "required": true,
+            "index": 1,
+            "top_level_field": true,
+            "url": "https://www.elastic.co/guide/en/ecs/current/ecs-log.html",
+            "comment": [
+                "This field SHOULD NOT be a nested object field but at the top level with a dot in the property name.",
+                "This is to make the JSON logs more human-readable.",
+                "Loggers MAY indent the log level so that the `message` field always starts at the exact same offset,",
+                "no matter the number of characters the log level has.",
+                "For example: `'DEBUG'` (5 chars) will not be indented, whereas ` 'WARN'` (4 chars) will be indented by one space character."
+            ]
+        },
+        "message": {
+            "type": "string",
+            "required": true,
+            "index": 2,
+            "url": "https://www.elastic.co/guide/en/ecs/current/ecs-base.html"
+        },
+        "ecs.version": {
+            "type": "string",
+            "required": true,
+            "url": "https://www.elastic.co/guide/en/ecs/current/ecs-ecs.html"
+        },
+        "labels": {
+            "type": "object",
+            "required": false,
+            "url": "https://www.elastic.co/guide/en/ecs/current/ecs-base.html",
+            "sanitization": {
+                "key": {
+                    "replacements": [
+                        ".",
+                        "*",
+                        "\\"
+                    ],
+                    "substitute": "_"
+                }
+            }
+        },
+        "trace.id": {
+            "type": "string",
+            "required": false,
+            "url": "https://www.elastic.co/guide/en/ecs/current/ecs-tracing.html",
+            "comment": "When APM agents add this field to the context, ecs loggers should pick it up and add it to the log event."
+        },
+        "transaction.id": {
+            "type": "string",
+            "required": false,
+            "url": "https://www.elastic.co/guide/en/ecs/current/ecs-tracing.html",
+            "comment": "When APM agents add this field to the context, ecs loggers should pick it up and add it to the log event."
+        },
+        "service.name": {
+            "type": "string",
+            "required": false,
+            "url": "https://www.elastic.co/guide/en/ecs/current/ecs-service.html",
+            "comment": [
+                "Configurable by users.",
+                "When an APM agent is active, they should auto-configure it if not already set."
+            ]
+        },
+        "event.dataset": {
+            "type": "string",
+            "required": false,
+            "url": "https://www.elastic.co/guide/en/ecs/current/ecs-event.html",
+            "default": "${service.name}.log OR ${service.name}.${appender.name}",
+            "comment": [
+                "Configurable by users.",
+                "If the user manually configures the service name,",
+                "the logging library should set `event.dataset=${service.name}.log` if not explicitly configured otherwise.",
+                "",
+                "When agents auto-configure the app to use an ECS logger,",
+                "they should set `event.dataset=${service.name}.${appender.name}` if the appender name is available in the logging library.",
+                "Otherwise, agents should also set `event.dataset=${service.name}.log`",
+                "",
+                "The field helps to filter for different log streams from the same pod, for example and is required for log anomaly detection."
+            ]
+        },
+        "process.thread.name": {
+            "type": "string",
+            "required": false,
+            "url": "https://www.elastic.co/guide/en/ecs/current/ecs-process.html"
+        },
+        "log.logger": {
+            "type": "string",
+            "required": false,
+            "url": "https://www.elastic.co/guide/en/ecs/current/ecs-log.html"
+        },
+        "log.origin.file.line": {
+            "type": "integer",
+            "required": false,
+            "url": "https://www.elastic.co/guide/en/ecs/current/ecs-log.html",
+            "comment": "Should be opt-in as it requires the logging library to capture a stack trace for each log event."
+        },
+        "log.origin.file.name": {
+            "type": "string",
+            "required": false,
+            "url": "https://www.elastic.co/guide/en/ecs/current/ecs-log.html",
+            "comment": "Should be opt-in as it requires the logging library to capture a stack trace for each log event."
+        },
+        "log.origin.function": {
+            "type": "string",
+            "required": false,
+            "url": "https://www.elastic.co/guide/en/ecs/current/ecs-log.html",
+            "comment": "Should be opt-in as it requires the logging library to capture a stack trace for each log event."
+        },
+        "error.type": {
+            "type": "string",
+            "required": false,
+            "url": "https://www.elastic.co/guide/en/ecs/current/ecs-error.html",
+            "comment": "The exception type or class, such as `java.lang.IllegalArgumentException`."
+        },
+        "error.message": {
+            "type": "string",
+            "required": false,
+            "url": "https://www.elastic.co/guide/en/ecs/current/ecs-error.html",
+            "comment": "The message of the exception."
+        },
+        "error.stack_trace": {
+            "type": "string",
+            "required": false,
+            "url": "https://www.elastic.co/guide/en/ecs/current/ecs-error.html",
+            "comment": "The stack trace of the exception as plain text."
+        }
+    }
+}
\ No newline at end of file
diff --git a/tests/test_apm.py b/tests/test_apm.py
index 2497d55..81d3e21 100644
--- a/tests/test_apm.py
+++ b/tests/test_apm.py
@@ -10,7 +10,7 @@
 from .compat import StringIO
 
 
-def test_elasticapm_structlog_log_correlation_ecs_fields():
+def test_elasticapm_structlog_log_correlation_ecs_fields(spec_validator):
     apm = elasticapm.Client({"SERVICE_NAME": "apm-service", "DISABLE_SEND": True})
     stream = StringIO()
     logger = structlog.PrintLogger(stream)
@@ -30,7 +30,7 @@ def test_elasticapm_structlog_log_correlation_ecs_fields():
     finally:
         apm.end_transaction("test-transaction")
 
-    ecs = json.loads(stream.getvalue().rstrip())
+    ecs = json.loads(spec_validator(stream.getvalue().rstrip()))
     ecs.pop("@timestamp")
     assert ecs == {
         "ecs": {"version": "1.6.0"},
diff --git a/tests/test_stdlib_formatter.py b/tests/test_stdlib_formatter.py
index c125479..c2ed87a 100644
--- a/tests/test_stdlib_formatter.py
+++ b/tests/test_stdlib_formatter.py
@@ -35,17 +35,17 @@ def make_record():
     return record
 
 
-def test_record_formatted():
+def test_record_formatted(spec_validator):
     formatter = ecs_logging.StdlibFormatter(exclude_fields=["process"])
 
-    assert formatter.format(make_record()) == (
+    assert spec_validator(formatter.format(make_record())) == (
         '{"@timestamp":"2020-03-20T14:12:46.123Z","log.level":"debug","message":"1: hello","ecs":{"version":"1.6.0"},'
         '"log":{"logger":"logger-name","origin":{"file":{"line":10,"name":"file.py"},"function":"test_function"},'
         '"original":"1: hello"}}'
     )
 
 
-def test_can_be_overridden():
+def test_can_be_overridden(spec_validator):
     class CustomFormatter(ecs_logging.StdlibFormatter):
         def format_to_ecs(self, record):
             ecs_dict = super(CustomFormatter, self).format_to_ecs(record)
@@ -53,7 +53,7 @@ def format_to_ecs(self, record):
             return ecs_dict
 
     formatter = CustomFormatter(exclude_fields=["process"])
-    assert formatter.format(make_record()) == (
+    assert spec_validator(formatter.format(make_record())) == (
         '{"@timestamp":"2020-03-20T14:12:46.123Z","log.level":"debug","message":"1: hello",'
         '"custom":"field","ecs":{"version":"1.6.0"},"log":{"logger":"logger-name","origin":'
         '{"file":{"line":10,"name":"file.py"},"function":"test_function"},"original":"1: hello"}}'
diff --git a/tests/test_structlog_formatter.py b/tests/test_structlog_formatter.py
index 4a48da5..9771d54 100644
--- a/tests/test_structlog_formatter.py
+++ b/tests/test_structlog_formatter.py
@@ -9,11 +9,11 @@ def make_event_dict():
 
 
 @mock.patch("time.time")
-def test_event_dict_formatted(time):
+def test_event_dict_formatted(time, spec_validator):
     time.return_value = 1584720997.187709
 
     formatter = ecs_logging.StructlogFormatter()
-    assert formatter(None, "debug", make_event_dict()) == (
+    assert spec_validator(formatter(None, "debug", make_event_dict())) == (
         '{"@timestamp":"2020-03-20T16:16:37.187Z","log.level":"debug",'
         '"message":"test message","ecs":{"version":"1.6.0"},'
         '"log":{"logger":"logger-name"}}'
@@ -21,7 +21,7 @@ def test_event_dict_formatted(time):
 
 
 @mock.patch("time.time")
-def test_can_be_set_as_processor(time):
+def test_can_be_set_as_processor(time, spec_validator):
     time.return_value = 1584720997.187709
 
     stream = StringIO()
@@ -35,7 +35,7 @@ def test_can_be_set_as_processor(time):
     logger = structlog.get_logger("logger-name")
     logger.debug("test message", custom="key", **{"dot.ted": 1})
 
-    assert stream.getvalue() == (
+    assert spec_validator(stream.getvalue()) == (
         '{"@timestamp":"2020-03-20T16:16:37.187Z","log.level":"debug",'
         '"message":"test message","custom":"key","dot":{"ted":1},'
         '"ecs":{"version":"1.6.0"}}\n'