otel

OpenTelemetry Example

Demonstrates server-level tracing with OTLP span export.

Spans are emitted for tools/list and tools/call requests. The initialize request and lifecycle notifications do not emit spans.

Prerequisites

• Docker (for Jaeger)
• wasm-tools (cargo install wasm-tools) to compile WAT to WASM

Run

1. Start Jaeger:

docker compose up -d

2. Compile the example component:

wasm-tools parse add-two.wat -o add-two.wasm

3. Start toolbelt:

cargo run -- config.toml add-two.wasm

4. Initialize a session, list tools, and call a tool using the curl scripts:

../curl/initialize.sh
../curl/list_tools.sh
../curl/call_tool.sh add-two.add-two x=5

5. View traces at http://localhost:16686 with service mcp.

With trace propagation

Per the MCP spec, trace context propagates via _meta in the request params, not via HTTP headers. Include traceparent (and optionally tracestate) inside params._meta:

curl -X POST http://localhost:3001/mcp \
  -H "Content-Type: application/json" \
  -H "Accept: application/json, text/event-stream" \
  -H "MCP-Session-Id: $SESSION_ID" \
  -d '{"jsonrpc":"2.0","id":4,"method":"tools/call","params":{"name":"add-two.add-two","arguments":{"x":5},"_meta":{"traceparent":"00-0af7651916cd43dd8448eb211c80319c-b7ad6b7169203331-01"}}}'

The tools/call add-two.add-two span should appear as a child of trace 0af7651916cd43dd8448eb211c80319c.