diff --git a/docs/api/advanced/artifacts.md b/docs/api/advanced/artifacts.md
index 67b121f9d998..9fdcd6588835 100644
--- a/docs/api/advanced/artifacts.md
+++ b/docs/api/advanced/artifacts.md
@@ -64,6 +64,12 @@ The `TestArtifactBase` interface is the base for all test artifacts.
 
 Extend this interface when creating custom test artifacts. Vitest automatically manages the `attachments` array and injects the `location` property to indicate where the artifact was created in your test code.
 
+::: danger
+When running with [`api.allowWrite`](/config/api#api-allowwrite) or [`browser.api.allowWrite`](/config/browser/api#api-allowwrite) disabled, Vitest empties the `attachments` array on every artifact before reporting it.
+
+If your custom artifact narrows the `attachments` type (e.g. to a tuple), include `| []` in the union so the type reflects what actually happens at runtime.
+:::
+
 ### `TestAttachment`
 
 ```ts
@@ -109,6 +115,7 @@ Here are a few guidelines or best practices to follow:
 - Try using a `Symbol` as the **registry key** to guarantee uniqueness
 - The `type` property should follow the pattern `'package-name:artifact-name'`, **`'internal:'` is a reserved prefix**
 - Use `attachments` to include files or data; extend [`TestAttachment`](#testattachment) for custom metadata
+- If you narrow the `attachments` type (e.g. to a tuple), include `| []` in the union since Vitest may empty the array at runtime (see [`TestArtifactBase`](#testartifactbase))
 - `location` property is automatically injected
 
 ## Custom Artifacts
@@ -127,7 +134,7 @@ interface AccessibilityArtifact extends TestArtifactBase {
   type: 'a11y:report'
   passed: boolean
   wcagLevel: 'A' | 'AA' | 'AAA'
-  attachments: [A11yReportAttachment]
+  attachments: [A11yReportAttachment] | []
 }
 
 const a11yReportKey = Symbol('report')
diff --git a/packages/runner/src/types/tasks.ts b/packages/runner/src/types/tasks.ts
index dd03229a6114..1c231c255d9b 100644
--- a/packages/runner/src/types/tasks.ts
+++ b/packages/runner/src/types/tasks.ts
@@ -1293,6 +1293,8 @@ export interface TestArtifactLocation extends FileLocation {}
  * Base interface for all test artifacts.
  *
  * Extend this interface when creating custom test artifacts. Vitest automatically manages the `attachments` array and injects the `location` property to indicate where the artifact was created in your test code.
+ *
+ * **Important**: when running with [`api.allowWrite`](https://vitest.dev/config/api#api-allowwrite) or [`browser.api.allowWrite`](https://vitest.dev/config/browser/api#api-allowwrite) disabled, Vitest empties the `attachments` array on every artifact before reporting it.
  */
 export interface TestArtifactBase {
   /** File or data attachments associated with this artifact */