feat: MCP by MathurAditya724 · Pull Request #864 · getsentry/spotlight

MathurAditya724 · 2025-08-01T22:06:22Z

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vercel · 2025-08-01T22:06:47Z

@MathurAditya724 is attempting to deploy a commit to the Sentry Team on Vercel.

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BYK

Good start!

We'd also need some tests, even if they are cursory like just making sure we can connect to the /mcp endpoint. Happy to help with that once we are further down the road with this PR.

packages/sidecar/src/main.ts

packages/sidecar/src/mcp.ts

packages/sidecar/src/messageBuffer.ts

BYK

Looking much better. I think we can clear out some of my questions in a meeting and see how we can get this merged ASAP.

BYK · 2025-08-05T10:37:21Z

packages/sidecar/src/mcp/index.ts

-import { MessageBuffer } from "./messageBuffer.js";
-import type { Payload } from "./utils.js";
+import type { TextContent } from "@modelcontextprotocol/sdk/types.js";
+import packageJson from "../../package.json" with { type: "json" };


Cannot do this due to fossilized binaries.

spotlight/packages/spotlight/bin/instrument.js

Line 6 in f5b6711

release: `spotlight@${process.env.npm_package_version}`,

is a way (which requires embedding that value during the build process)

BYK · 2025-08-05T14:01:31Z

packages/sidecar/src/mcp/index.ts

+        .map(([contentType, data]) => processEnvelope({ contentType, data }))
+        .sort((a, b) => {


We can probably move that event.type === "event" check here and save some memory and CPU time. It wold also allow us to do

const content = errors.map(payload => ({...}));

which should also be more efficient than someArray.push().

i think instead of event.type === "event" we should check something like this

spotlight/packages/overlay/src/integrations/sentry/utils/sentry.ts

Line 10 in f5b6711

export function isErrorEvent(event: SentryEvent): event is SentryErrorEvent {

because we only need error events here.

and why not check this in the errorBuffer itself?

BYK · 2025-08-05T14:02:30Z

packages/sidecar/src/mcp/parsing.ts

@@ -0,0 +1,66 @@
+type RawEventContext = {


Might be good to add a top-level comment about where this code came from and our future plans of splitting this out.

BYK · 2025-08-05T14:04:18Z

packages/sidecar/src/main.ts

        return;
      }
-      return handler(req, res, pathname, searchParams);
+      return (await handler)(req, res, pathname, searchParams);


I do not like awaiting a handler every single time we get a request. It adds at least one tick to everything. Can we find a better way to do this? I'm happy doing await mcp.connect() at the start of the server and delay that once rather than doing this.

BYK · 2025-08-05T14:07:12Z

packages/sidecar/src/messageBuffer.ts

@@ -68,10 +68,16 @@ export class MessageBuffer<T> {
  }

  read(): T[] {


This does something very similar to .stream() method above so we should align them or make them share some code. Also it might be wise to make start an argument but defaulting to this.head for different clients being at different places?

Shubhdeep12 · 2025-08-05T16:03:44Z

packages/sidecar/src/main.ts

  }
+
+  // MCP Setup
+  const transport = new StreamableHTTPServerTransport({


I think we should not create an MCP server instance every time. Instead, we should move the initialization logic to handleMCPRequest.

also in handleMCPRequest, we should initiate MCP server only in first API call
something like-

let mcpServerInstance: McpServer; let mcpTransport: StreamableHTTPServerTransport; async function handleMcpRequest(): Promise<RequestHandler> { if (!mcpServerInstance) { mcpTransport = new StreamableHTTPServerTransport({ sessionIdGenerator: undefined, }); mcpServerInstance = createMcpInstance(buffer); await mcpServerInstance.connect(mcpTransport); } return (req, res) => mcpTransport.handleRequest(req, res); }

however i think this approach also can cause an issue with concurrent requests - if multiple requests arrive simultaneously before initialization is complete, they could all try to initialize the server at the same time.

BYK

This addresses all my blockers so unblocking. Great work!

vercel · 2025-08-05T20:13:41Z

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Name	Status	Preview	Comments	Updated (UTC)
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Copilot

Pull Request Overview

This PR adds Model Context Protocol (MCP) support to the Spotlight sidecar, enabling AI assistants to fetch recent error data for debugging purposes.

Implements MCP server with error retrieval tools
Adds new HTTP endpoint /mcp for MCP communication
Extracts shared types and adds envelope parsing utilities

Reviewed Changes

Copilot reviewed 7 out of 8 changed files in this pull request and generated 4 comments.

Show a summary per file

File	Description
packages/sidecar/tsdown.config.ts	Removes external dependencies configuration from build config
packages/sidecar/src/utils.ts	Defines shared Payload type
packages/sidecar/src/messageBuffer.ts	Adds read() method to MessageBuffer class
packages/sidecar/src/mcp/parsing.ts	Implements Sentry envelope parsing utilities
packages/sidecar/src/mcp/index.ts	Creates MCP server instance with error retrieval tool
packages/sidecar/src/main.ts	Integrates MCP server and adds /mcp endpoint
packages/sidecar/package.json	Adds MCP SDK dependencies and fixes export paths

Copilot · 2025-08-05T21:47:04Z

packages/sidecar/src/mcp/parsing.ts

+        // @ts-expect-error ts(2339) -- We should really stop adding type to payloads
+        itemPayload.type = itemHeader.type;


The @ts-expect-error comment indicates a known type safety issue. Consider defining proper types for itemPayload or using a type assertion instead of suppressing the error.

Suggested change

// @ts-expect-error ts(2339) -- We should really stop adding type to payloads

itemPayload.type = itemHeader.type;

(itemPayload as Record<string, unknown>).type = itemHeader.type;

Copilot · 2025-08-05T21:47:04Z

packages/sidecar/src/mcp/parsing.ts

+export function parseJSONFromBuffer<T = unknown>(data: Uint8Array): T {
+  try {
+    return JSON.parse(new TextDecoder().decode(data)) as T;
+  } catch (err) {
+    console.error(err);
+    return {} as T;


Returning an empty object when JSON parsing fails could cause runtime errors if the caller expects specific properties. Consider returning null or throwing a more specific error instead of masking the failure.

Suggested change

export function parseJSONFromBuffer<T = unknown>(data: Uint8Array): T {

try {

return JSON.parse(new TextDecoder().decode(data)) as T;

} catch (err) {

console.error(err);

return {} as T;

export function parseJSONFromBuffer<T = unknown>(data: Uint8Array): T | null {

try {

return JSON.parse(new TextDecoder().decode(data)) as T;

} catch (err) {

console.error(err);

return null;

Copilot · 2025-08-05T21:47:04Z

packages/sidecar/src/mcp/index.ts

+    "Fetches the most recent errors from Spotlight debugger. Returns error details, stack traces, and request details for immediate debugging context.",
+    async () => {
+      const envelopes = errorsBuffer.read();
+      errorsBuffer.clear();


Clearing the errors buffer after reading means subsequent calls to get_errors will return empty results until new errors occur. This could lead to data loss if multiple consumers try to access errors or if the tool is called multiple times.

Suggested change

errorsBuffer.clear();

Copilot · 2025-08-05T21:47:05Z

packages/sidecar/src/messageBuffer.ts

+    for (let i = start; i < end; i++) {
+      const item = this.items[i % this.size];
+      if (item !== undefined) {
+        result.push(item[1]);


The read() method accesses item[1] but the MessageBuffer stores items of type T directly, not as tuples. This will cause a runtime error since T items don't have an index [1].

MathurAditya724 and others added 4 commits July 21, 2025 21:30

feat: basic mcp setup

299a337

chore: minor improvements

4ff8ab5

fix: completed the basic draft of the mcp server

3ebee1a

fix: added a prompt for failed elicitInput

35b8b07

MathurAditya724 requested a review from Copilot August 1, 2025 22:06

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MathurAditya724 added 2 commits August 1, 2025 15:09

chore: minor changes

b9cabbe

chore: remove elicitInput

2614f6b

BYK requested changes Aug 4, 2025

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packages/sidecar/src/main.ts Outdated Show resolved Hide resolved

packages/sidecar/src/mcp.ts Outdated Show resolved Hide resolved

packages/sidecar/src/mcp.ts Outdated Show resolved Hide resolved

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MathurAditya724 added 4 commits August 4, 2025 09:19

chore: matched the mcp's version with sidecar

b560cac

chore: shifted mcp connect logic in the setup process

325a0ca

chore: improved the read function logic

81ead5e

chore: improved the parsing logic

18f7ca4

BYK requested changes Aug 5, 2025

View reviewed changes

Shubhdeep12 reviewed Aug 5, 2025

View reviewed changes

MathurAditya724 added 3 commits August 5, 2025 09:08

chore: corrected the mcp version

6881c70

feat: added issue formatting code

a3160e0

chore: minor changes

84c7bd6

BYK approved these changes Aug 5, 2025

View reviewed changes

MathurAditya724 added 2 commits August 5, 2025 12:59

chore: removed the formatting stuff for now

168b70e

chore: removed zod

d114019

vercel bot deployed to Preview August 5, 2025 20:14 View deployment

MathurAditya724 and others added 3 commits August 5, 2025 13:21

Merge branch 'main' into merge-mcp

f5f0c43

chore: updated the lockfile

c54bb2a

fix: corrected the handler function and minor changes

c2cff7d

MathurAditya724 marked this pull request as ready for review August 5, 2025 21:37

MathurAditya724 requested a review from Copilot August 5, 2025 21:46

Copilot AI reviewed Aug 5, 2025

View reviewed changes

vercel bot deployed to Preview August 5, 2025 21:47 View deployment

MathurAditya724 enabled auto-merge (squash) August 5, 2025 22:16

MathurAditya724 merged commit 3ae77a5 into getsentry:main Aug 5, 2025
22 of 25 checks passed

MathurAditya724 deleted the merge-mcp branch August 5, 2025 22:36

		.map(([contentType, data]) => processEnvelope({ contentType, data }))
		.sort((a, b) => {

		@@ -68,10 +68,16 @@ export class MessageBuffer<T> {
		}

		read(): T[] {

		// @ts-expect-error ts(2339) -- We should really stop adding type to payloads
		itemPayload.type = itemHeader.type;

	// @ts-expect-error ts(2339) -- We should really stop adding type to payloads
	itemPayload.type = itemHeader.type;
	(itemPayload as Record<string, unknown>).type = itemHeader.type;

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