instrument-mcp-server

Amplitude MCP Analytics Setup

Instruments an MCP server so every tool call becomes an Amplitude event, joinable with the rest of the product's Amplitude data (retention, revenue, web/mobile usage).

The authoritative SDK reference is the package README: https://github.com/amplitude/Amplitude-MCP-Analytics-Node (npm: @amplitude/mcp-analytics). The SDK is in preview and evolves quickly — always fetch the latest README and follow it for installation, API shapes, configuration, and default events. Do not rely on memorized snippets or this skill's summaries for SDK API details; the README wins on any conflict.

There are four steps. Steps 1–2 are required and are documented in the README — this skill tells you which sections to follow and which invariants to verify. Steps 3–4 are strongly recommended and are documented in full here, because they require changes outside the SDK (the server's tool schemas and the product's web app) that the SDK README intentionally does not cover.

Do them in order: Step 1 (tool calls) → Step 2 (identity) → Step 3 (rationale) → Step 4 (UTM, only if the server returns links). Get identity right before calling anything "done" — everything downstream depends on it.

Before you start

Confirm:

1. This is a Node/TypeScript MCP server built on @modelcontextprotocol/sdk. This SDK doesn't support other languages/runtimes.
2. The user has (or can get) an Amplitude API key for the project they want events to land in.
3. Which package manager the repo uses (pnpm/npm/yarn) — adjust the install command accordingly.

Step 1 — Install the SDK and track tool calls (required)

Fetch the README and follow its Install and Quick start sections. Always install the latest published version (e.g. pnpm add @amplitude/mcp-analytics@latest) — never pin a version from memory, and don't reproduce install commands from this skill.

Invariants to verify once wired up (the README explains each):

• analytics.instrumentServer(server, ...) runs before server.connect() — order matters.
• Every tool handler is wrapped with analytics.instrumentTool(...). Unwrapped tools aren't tracked. The wrapper has the identical shape to the handler and is a no-op passthrough if the server was never bound, so it's safe to wrap defensively.
• Default events all carry the [MCP] prefix, so they never collide with the product's existing Amplitude events. See the README's Default events table (and docs/events.md in the repo) for the current event set and properties.

Optional: attach stable custom dimensions (plan tier, team, feature flags) via extra on instrumentTool/instrumentServer — see the README's Custom event properties section.

Step 2 — Get identity right (required, do this before calling Step 1 "done")

MCP events must carry the same user_id the product already sends to Amplitude from web/mobile. Skip this and MCP usage shows up as a disconnected population that can't be joined to product data — this defeats most of the point of the integration.

Follow the README's Identity section for the current API: it offers server-level binding, per-request setIdentity() inside a handler, and an opt-in resolveIdentity mapping from the request's authInfo claims. Pick whichever fits the server's auth model.

One behavior to surface to the user: fully anonymous, anchor-less events are dropped by default (not counted as users) unless explicitly opted in via emitAnonymousEvent: true for aggregate-only tracking — ask before turning this on, since it changes what gets counted.

Step 3 — Capture rationale (recommended)

Unlike a human clicking a button, an agent can tell you why it called a tool. Capturing this turns the data from "what happened" into "what the user was trying to do."

The SDK side is one call (analytics.setRationale(...) — see the README's Rationale section), but the SDK never reads rationale out of tool inputs itself: how the rationale reaches the server is a server-side convention this skill implements. The battle-tested pattern is schema injection — add an optional rationale field to every tool's input schema. Because the parameter is described in the schema agents already read, they fill it in unprompted, across all clients, with zero client-side changes:

// Add to every tool's input schema (zod example):
rationale: z
  .string()
  .optional()
  .describe(
    'Brief explanation of why you are calling this tool and what ' +
    'you expect to learn from the result.',
  ),

Then read it inside the instrumented handler and hand it to the SDK:

analytics.instrumentTool(async (args, extra) => {
  if (typeof args.rationale === 'string') {
    analytics.setRationale(args.rationale);
  }
  return doWork(args);
}, { name: 'search' });

Making the field optional means nothing breaks when an agent omits it. It is emitted as the reserved [MCP] Rationale property (truncated to 1,000 chars; last write wins). Worth doing on every tool, not just a sample.

Step 4 — UTM-tag outbound links (recommended, only if the server returns URLs)

This step is entirely outside the SDK — it changes how the server builds URLs and depends on the product's web-side analytics. It is not covered in the SDK README.

If any tool response includes a link (dashboard, doc, product page), tag it before it leaves the server so click-throughs are attributable to MCP/agent traffic instead of showing up as direct:

function addUtmParams(url: string, clientName?: string): string {
  const u = new URL(url);
  u.searchParams.append('utm_source', 'mcp');
  u.searchParams.append('utm_medium', 'referral');
  // The connected client (e.g. "Claude", "Cursor"), if you know it:
  u.searchParams.append('utm_content', clientName ?? 'unknown');
  return u.toString();
}

Route every URL-building path in tool responses through one central function like this — a single untagged link breaks the attribution story for that flow.

Prerequisite (tell the user this explicitly): this only works if their web analytics captures UTM params on page-view events (or whatever event their site fires on landing). Amplitude's Browser SDK 2 does this by default — see Track marketing attribution (UTM, referrer, and click ID parameters are captured out of the box). If they use a custom page-view tracker, they need to confirm UTM values land on those events too, or there's nothing to join the MCP-tagged clicks against.

Relevant Amplitude documentation:

• Browser SDK 2 — Track marketing attribution (web-side UTM capture, the implementation half of this step)
• Sessions, channels, and attribution for marketing analytics (how the tagged traffic becomes channel analysis)
• Autocapture (page views and more)

After instrumenting

Once events are flowing, point a coding agent at Amplitude's published analyze-mcp-server skill to run intent clustering and surface tool-call error patterns by intent. (If this project has the mcp-intent-error-analysis skill installed, that's the one — use it once the user has data flowing and wants to analyze it, rather than duplicating that analysis here.)

Common mistakes to flag

• Following stale API snippets instead of the current README — fetch it fresh; the SDK is in preview and moves fast.
• Installing a pinned/older version instead of the latest release.
• Calling instrumentServer() after server.connect() — must be before.
• Wrapping some tool handlers but not others — every tool needs instrumentTool.
• Sending a user_id that doesn't match the one used on web/mobile — breaks joinability, the whole point of the integration.
• Turning on emitAnonymousEvent: true without the user understanding it inflates aggregate counts with anchor-less traffic.
• Forgetting the UTM prerequisite (web-side capture) and assuming tagging links alone is sufficient.