The trace format

A trace is JSON Lines: one event per line. Each event carries a capture-assigned seq (the only ordering authority — never inferred later), a direction (client-to-server / server-to-client), a transport, and a kind:

• message events hold the JSON-RPC payload verbatim;
• http events record the status and the conformance-relevant headers; and
• lifecycle events mark transport open/close.

The full schema, including the redaction rules that keep credential-bearing headers out of a trace by construction, is in 02-architecture.md and 05-security-model.md.

One worked example

The example below is embedded verbatim from the README, where a test (readme_examples.rs) pins it to the validator’s real output — so what you read here cannot drift from what the tool actually produces. It is a session that reuses a request ID, and the verdict that catches it:

{"seq":0,"direction":"client-to-server","transport":"stdio","kind":"message","payload":{"jsonrpc":"2.0","id":1,"method":"initialize","params":{"protocolVersion":"2025-11-25","capabilities":{},"clientInfo":{"name":"my-host","version":"1.0.0"}}}}
{"seq":1,"direction":"server-to-client","transport":"stdio","kind":"message","payload":{"jsonrpc":"2.0","id":1,"result":{"protocolVersion":"2025-11-25","capabilities":{"tools":{}},"serverInfo":{"name":"my-server","version":"1.0.0"}}}}
{"seq":2,"direction":"client-to-server","transport":"stdio","kind":"message","payload":{"jsonrpc":"2.0","method":"notifications/initialized"}}
{"seq":3,"direction":"client-to-server","transport":"stdio","kind":"message","payload":{"jsonrpc":"2.0","id":1,"method":"tools/list"}}

and the validator answers with the violated clause, verbatim from the spec via the registry, addressed to the offending event:

  FAIL  BASE-003 (MUST NOT)
        seq 3: request "tools/list" reuses id 1, already used by the same party at seq 0
totals: 45 pass, 1 fail, 0 warn, 88 excluded, 0 unsupported, 6 not applicable
verdict: fail

The totals line distinguishes the verdict’s components: the five not-applicable rows are capability-gated requirements this session never negotiated (the resources and prompts clauses) — reported as such, never as passes. See Architecture for why that distinction is load-bearing.