Add OTEL tracing to the sampling pipeline:
- `sampling/createMessage` span wrapping sample_impl() with attributes for
temperature, max_tokens, tool_count, result_type, and iteration count
- `sampling/createMessage step` child spans per loop iteration with
iteration index and stop reason
- `sampling.execute_tool <name>` spans for tool calls within sampling,
including error status on failures
- Validation failure and text response retry events on the parent span
- Opt-in content capture via OTEL_INSTRUMENTATION_GENAI_CAPTURE_MESSAGE_CONTENT
Also adds is_recording() guards to server_span, delegate_span, and
client_span to avoid unnecessary attribute serialization when sampling is
disabled, and sets error.type using __qualname__ for better nested class
names.
Closes#3891
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
Updates FastMCP's telemetry to align with the new MCP semantic conventions
from open-telemetry/semantic-conventions#2083. This gives us interoperability
with other MCP implementations while keeping fastmcp.* attributes for things
unique to our framework.
Changes:
- Span names now follow `{method} {target}` format (e.g., `tools/call greet`)
- Added `mcp.method.name` and `mcp.resource.uri` attributes
- Renamed `fastmcp.session.id` to standard `mcp.session.id`
- Kept fastmcp.* attributes for server name, component info, provider details
🤖 Generated with Claude Code
Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>
Adds opt-in distributed tracing via OpenTelemetry for observability into
FastMCP server and client operations.
Server spans are created for tool calls, resource reads, and prompt
renders with attributes like component key, component type, provider
type, session ID, and auth context. Client spans wrap outgoing calls
with trace context propagation via W3C headers in request meta.
Components provide their own span attributes through a `get_span_attributes()`
method that subclasses override - this lets LocalProvider, FastMCPProvider,
and ProxyProvider each include relevant context (original names, backend URIs).
To enable: configure an OpenTelemetry SDK with a TracerProvider before
importing fastmcp. Traces export to any OTLP-compatible backend.
Closes ENG-2813
🤖 Generated with Claude Code
Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>
