Telemetry API

The this.telemetry API is available on all execution contexts (ToolContext, ResourceContext, PromptContext, AgentContext) when observability is enabled. It provides a simple interface for creating custom spans, recording events, and setting attributes — with automatic trace context propagation.

Requires @frontmcp/observability installed and observability config enabled. See the Observability Guide for setup.

TelemetryAccessor

Available as this.telemetry in all execution contexts. One instance per request (context-scoped). Automatically inherits the current request’s trace ID, session ID, and scope.

`startSpan(name, attributes?)`

Create a child span under the current execution span.

startSpan(name: string, attributes?: Record<string, string | number | boolean>): TelemetrySpan

You must call span.end() or span.endWithError() when done.

const span = this.telemetry.startSpan('fetch-user', { 'user.id': userId });
try {
  const user = await this.fetch(`/api/users/${userId}`);
  span.setAttribute('user.name', user.name);
  span.end();
} catch (err) {
  span.endWithError(err);
  throw err;
}

`withSpan(name, fn, attributes?)`

Run a function within a span. The span is automatically ended on success or error.

withSpan<T>(
  name: string,
  fn: (span: TelemetrySpan) => Promise<T>,
  attributes?: Record<string, string | number | boolean>,
): Promise<T>

const data = await this.telemetry.withSpan('query-database', async (span) => {
  span.addEvent('query-sent');
  const results = await db.query(sql);
  span.setAttribute('rows', results.length);
  return results;
});

`addEvent(name, attributes?)`

Add an event to the active flow execution span (e.g., the tool span during execute()).

addEvent(name: string, attributes?: Record<string, string | number | boolean>): void

Events are lightweight markers that appear on the parent span’s timeline. Use them for milestones rather than creating child spans.

this.telemetry.addEvent('cache-checked', { hit: false });
this.telemetry.addEvent('validation-complete', { fields: 5 });

Events go on the active execution span, not a new span. If called during tool.execute(), they appear on the "tool my_tool" span. If called outside an execution context, a short-lived child span is created as a fallback.

`setAttributes(attrs)`

Set attributes on the active flow execution span.

setAttributes(attrs: Record<string, string | number | boolean>): void

this.telemetry.setAttributes({
  'user.tier': 'premium',
  'request.size': body.length,
  'cache.hit': true,
});

`traceId`

Get the current request’s trace ID. Useful for including in external API calls or logs.

get traceId(): string

const response = await this.fetch('/api/data', {
  headers: { 'X-Trace-Id': this.telemetry.traceId },
});

`sessionId`

Get the privacy-safe session tracing ID (16-char SHA-256 hash).

get sessionId(): string

TelemetrySpan

Returned by startSpan() and passed to withSpan() callbacks. All setter methods return this for chaining.

Methods

Method	Signature	Description
`setAttribute`	`(key: string, value: string \| number \| boolean) => this`	Set a single attribute
`setAttributes`	`(attrs: Record<string, string \| number \| boolean>) => this`	Set multiple attributes
`addEvent`	`(name: string, attributes?: Record<...>) => this`	Add a named event
`recordError`	`(error: Error) => this`	Record an exception on the span
`end`	`() => void`	End the span with OK status
`endWithError`	`(error: Error \| string) => void`	End with ERROR status
`raw`	`Span` (getter)	Access the underlying OTel Span

const span = this.telemetry.startSpan('process');
span
  .setAttribute('input.size', 1024)
  .addEvent('step-1-done')
  .addEvent('step-2-done', { items: 42 });

if (failed) {
  span.recordError(new Error('processing failed'));
}

span.end(); // Preserves ERROR status if recordError was called

Testing Utilities

Import from @frontmcp/observability:

import {
  createTestTracer,
  getFinishedSpans,
  assertSpanExists,
  assertSpanAttribute,
  findSpan,
  findSpansByAttribute,
} from '@frontmcp/observability';

`createTestTracer(name?)`

Create an isolated test tracer with in-memory span exporter. Does not register globally — safe for parallel tests.

function createTestTracer(name?: string): {
  tracer: Tracer;
  exporter: InMemorySpanExporter;
  provider: BasicTracerProvider;
  cleanup: () => Promise<void>;
}

const { tracer, exporter, cleanup } = createTestTracer();

afterEach(() => exporter.reset());
afterAll(() => cleanup());

`assertSpanExists(spans, name)`

Assert that a span with the given name exists. Returns the span or throws.

function assertSpanExists(spans: ReadableSpan[], name: string): ReadableSpan

const spans = getFinishedSpans(exporter);
const toolSpan = assertSpanExists(spans, 'tool get_weather');

`assertSpanAttribute(span, key, value)`

Assert a span has a specific attribute value.

function assertSpanAttribute(span: ReadableSpan, key: string, value: string | number | boolean): void

`findSpan(spans, name)` / `findSpansByAttribute(spans, key, value)`

Query helpers for finding spans in test assertions.

const dbSpan = findSpan(spans, 'database-query');
const toolSpans = findSpansByAttribute(spans, 'mcp.component.type', 'tool');

Configuration Types

ObservabilityOptionsInterface

The config object for @FrontMcp({ observability: { ... } }):

Property	Type	Default	Description
`tracing`	`boolean \| TracingOptions`	`true`	Enable/configure OTel tracing
`logging`	`boolean \| LoggingOptions`	`false`	Enable/configure structured logging
`requestLogs`	`boolean \| RequestLogOptions`	`false`	Enable/configure per-request log collection

TracingOptions

Property	Type	Default	Description
`httpSpans`	`boolean`	`true`	HTTP request spans
`executionSpans`	`boolean`	`true`	Tool/resource/prompt/agent spans
`fetchSpans`	`boolean`	`true`	Outbound `ctx.fetch()` spans
`flowStageEvents`	`boolean`	`true`	Flow stage events on execution spans
`hookSpans`	`boolean`	`false`	Individual hook spans (verbose)
`transportSpans`	`boolean`	`true`	SSE/HTTP transport spans
`authSpans`	`boolean`	`true`	Auth/session verify spans
`oauthSpans`	`boolean`	`true`	OAuth flow spans
`elicitationSpans`	`boolean`	`true`	Elicitation request/result spans
`startupReport`	`boolean`	`true`	Emit startup telemetry on first request

SinkConfig

Type	Description	Platform
`{ type: 'stdout' }`	NDJSON to stdout (12-factor)	Node.js
`{ type: 'console' }`	`console.log/warn/error`	Browser, Node.js
`{ type: 'otlp', endpoint, headers? }`	OTLP HTTP to any backend	Node.js
`{ type: 'winston', logger }`	Forward to winston instance	Node.js
`{ type: 'pino', logger }`	Forward to pino instance	Node.js
`{ type: 'callback', fn }`	Custom callback function	Any

Observability Guide

Step-by-step setup with vendor integrations

Observability Feature

Overview of what FrontMCP observability provides

Decorators

Core Classes

Registries

Guard

Telemetry

Errors

Nx Plugin

TelemetryAccessor

`startSpan(name, attributes?)`

`withSpan(name, fn, attributes?)`

`addEvent(name, attributes?)`

`setAttributes(attrs)`

`traceId`

`sessionId`

TelemetrySpan

Methods

Testing Utilities

`createTestTracer(name?)`

`assertSpanExists(spans, name)`

`assertSpanAttribute(span, key, value)`

`findSpan(spans, name)` / `findSpansByAttribute(spans, key, value)`

Configuration Types

ObservabilityOptionsInterface

TracingOptions

SinkConfig

Observability Guide

Observability Feature

​TelemetryAccessor

​startSpan(name, attributes?)

​withSpan(name, fn, attributes?)

​addEvent(name, attributes?)

​setAttributes(attrs)

​traceId

​sessionId

​TelemetrySpan

​Methods

​Testing Utilities

​createTestTracer(name?)

​assertSpanExists(spans, name)

​assertSpanAttribute(span, key, value)

​findSpan(spans, name) / findSpansByAttribute(spans, key, value)

​Configuration Types

​ObservabilityOptionsInterface

​TracingOptions

​SinkConfig

​Related

Observability Guide

Observability Feature

TelemetryAccessor

`startSpan(name, attributes?)`

`withSpan(name, fn, attributes?)`

`addEvent(name, attributes?)`

`setAttributes(attrs)`

`traceId`

`sessionId`

TelemetrySpan

Methods

Testing Utilities

`createTestTracer(name?)`

`assertSpanExists(spans, name)`

`assertSpanAttribute(span, key, value)`

`findSpan(spans, name)` / `findSpansByAttribute(spans, key, value)`

Configuration Types

ObservabilityOptionsInterface

TracingOptions

SinkConfig

Related