diff --git a/extension/.vscodeignore b/extension/.vscodeignore
index 786d358a..5e7de304 100644
--- a/extension/.vscodeignore
+++ b/extension/.vscodeignore
@@ -3,6 +3,7 @@
 # downloads from the servers on first use (ASSET_URLS in src/extension.ts).
 **
 !package.json
+!telemetry.json
 !README.md
 !CHANGELOG.md
 !LICENSE
diff --git a/extension/CHANGELOG.md b/extension/CHANGELOG.md
index ca4c4a42..6dec2b42 100644
--- a/extension/CHANGELOG.md
+++ b/extension/CHANGELOG.md
@@ -1,17 +1,5 @@
 # Changelog
 
-## Unreleased
-
-- Compiler and emulator crashes send an error report to 8bitworkshop.com,
-  following VS Code's `telemetry.telemetryLevel` setting. See the README.
-
-- The Atari 2600 now stops at breakpoints and steps by instruction, not by
-  frame, and can step back.
-- `.s`, `.asm`, `.inc` and `.a` files in a project get the highlighting
-  for the platform's CPU. `.acme` files get 6502 highlighting.
-- The platform list shows the 8bitworkshop book for each platform that
-  has one, with a button to open it.
-
 ## 0.1.0
 
 First preview.
@@ -23,3 +11,11 @@ First preview.
 - Emulator panel with pause, reset, and mute.
 - Syntax highlighting for 6502, Z80, and 6809 assembly.
 - Toolchains download on first use, checked against built-in hashes.
+- Compiler and emulator crashes send an error report to 8bitworkshop.com,
+  following VS Code's `telemetry.telemetryLevel` setting. See the README.
+- The Atari 2600 now stops at breakpoints and steps by instruction, not by
+  frame, and can step back.
+- `.s`, `.asm`, `.inc` and `.a` files in a project get the highlighting
+  for the platform's CPU. `.acme` files get 6502 highlighting.
+- The platform list shows the 8bitworkshop book for each platform that
+  has one, with a button to open it.
diff --git a/extension/README.md b/extension/README.md
index 2c99da63..900b24d4 100644
--- a/extension/README.md
+++ b/extension/README.md
@@ -121,10 +121,14 @@ and Open Example lists show which platforms have one.
 ## Error reports
 
 When a compiler or the emulator crashes, the extension sends an error report
-to 8bitworkshop.com: the error message, stack trace, platform, tool, and
-VS Code and extension versions. It doesn't send your source files. Errors in your
-program, like a syntax error or a crash in the emulated machine, aren't
-reported.
+to 8bitworkshop.com: the error message, stack trace, platform, and tool, plus
+VS Code and extension versions. It doesn't send your source files, and VS Code
+removes file paths from the report before it leaves. Errors in your program,
+like a syntax error or a crash in the emulated machine, aren't reported.
+
+VS Code attaches identifiers to every report: a machine id (stable for your
+VS Code install, not tied to your identity), a session id, and a device id.
+These group reports from one install together.
 
 The reports follow VS Code's `telemetry.telemetryLevel` setting: set it to
 `off` to stop them.
diff --git a/extension/telemetry.json b/extension/telemetry.json
new file mode 100644
index 00000000..011e1299
--- /dev/null
+++ b/extension/telemetry.json
@@ -0,0 +1,44 @@
+{
+  "commonProperties": {},
+  "events": {
+    "error": {
+      "owner": "sehugg",
+      "comment": "A build tool, emulator, or extension failure, sent to 8bitworkshop.com/error.php. Gated on VS Code's telemetry.telemetryLevel through env.createTelemetryLogger; nothing is sent when telemetry is off. Uncaught errors from this extension use the same sender.",
+      "source": {
+        "classification": "SystemMetaData",
+        "purpose": "FeatureInsight",
+        "comment": "Where the failure came from: vscode, worker, emu, or ide."
+      },
+      "msg": {
+        "classification": "CallstackOrException",
+        "purpose": "PerformanceAndHealth",
+        "comment": "Error message, cleaned by VS Code and truncated to 2000 characters."
+      },
+      "stack": {
+        "classification": "CallstackOrException",
+        "purpose": "PerformanceAndHealth",
+        "comment": "Stack trace, with user paths scrubbed by VS Code, truncated to 2000 characters."
+      },
+      "clientTime": {
+        "classification": "SystemMetaData",
+        "purpose": "PerformanceAndHealth",
+        "comment": "ISO 8601 timestamp from the client."
+      },
+      "platform": {
+        "classification": "SystemMetaData",
+        "purpose": "FeatureInsight",
+        "comment": "Platform id, for example nes or c64."
+      },
+      "tool": {
+        "classification": "SystemMetaData",
+        "purpose": "FeatureInsight",
+        "comment": "Build tool id, for example cc65 or dasm."
+      },
+      "window": {
+        "classification": "SystemMetaData",
+        "purpose": "FeatureInsight",
+        "comment": "Window or workspace identifier, when provided."
+      }
+    }
+  }
+}