How to diff two Agent Protocol Inspector scans to catch MCP and A2A regressions — a removed tool, a dropped auth mechanism, a downgraded protocol status — in CI with curl and jq.
A REST API that silently drops an endpoint on deploy gets caught by a contract test, usually before it reaches production. An MCP server or A2A agent that silently drops a tool, loses its auth requirement, or downgrades its own protocol support has no equivalent gate — because there's no equivalent test suite. Every downstream agent integration finds out the hard way, at runtime, when a call it relied on stops existing.
Agent Protocol Inspector's scan diff exists to close exactly that gap: a structural comparison between two stored scans of the same target, producing a pass / warn / fail verdict a CI pipeline can actually act on.
What Gets Compared #
diffScans takes a baseline scan and a current scan and compares all three protocols structurally — no new network calls, no re-probing, just a pure comparison of two already-fetched results:
| Change | Verdict |
|---|---|
A protocol's detection status regressed ( confirmed →indicated ornot_detected ) |
fail |
| An MCP tool, A2A skill, or ARD catalog entry was removed | fail |
| A declared auth mechanism disappeared entirely | fail |
| A tool/skill/entry was added | warn |
| An existing MCP tool's input schema changed | warn |
| An auth mechanism changed (without disappearing) | warn |
| Nothing meaningfully changed | pass |
The asymmetry is deliberate. Removing something the agent could do before is a regression a downstream integration will break on — that's a fail. Adding new surface area is worth a human's attention but isn't inherently dangerous — that's a warn, not a build-breaker. A tool's input schema changing without being removed sits in the same bucket: worth reviewing, not worth blocking a deploy over on its own.
Wiring It Into CI #
The verdict is only useful if a pipeline can actually act on it — and a bare curl call can't. An HTTP 200 response with {"verdict":"fail"} in the body still makes curl exit 0; nothing about that response naturally breaks a CI step. The fix is a couple of lines of jq:
RESPONSE=$(curl -sS -X POST https://contextiq.trango-compute.com/api/v1/agent-protocol-inspector/compare \
-H "Authorization: Bearer $CONTEXTIQ_API_KEY" \
-H "Content-Type: application/json" \
-d '{"baselineScanId":"<last-deploy-scanId>","currentScanId":"<this-deploy-scanId>"}')
echo "$RESPONSE" | jq .
VERDICT=$(echo "$RESPONSE" | jq -r '.verdict')
if [ "$VERDICT" = "fail" ]; then
echo "Agent Protocol Inspector: regression detected — failing build." >&2
exit 1
fi
That's a real go/no-go gate: warn still prints the full diff for a human to read, but only fail stops the pipeline. This snippet is generated directly in the dashboard's "Compare against a prior scan" panel, next to the field where you'd paste in a baseline scanId to test manually before committing it to a workflow file.
A Practical Deploy-Gate Pattern #
The workflow this is built for:
- After every deploy , run a scan of your own MCP endpoint or A2A agent card and capture the returned
scanId. - Store that
scanIdsomewhere your next CI run can read it — a repo variable, a deploy artifact, a line in your release notes. - Before the next deploy goes live , run a fresh scan and diff it against the stored baseline using the snippet above.
- On
fail, the pipeline stops before the regression reaches users who were already depending on the tool or skill that disappeared.
This is the same shape as a contract test for a REST API — a stored "last known good" fingerprint, compared against every candidate release — applied to a surface (agent protocol conformance) that doesn't otherwise get tested at all.
What This Doesn't Catch #
A diff only knows what changed structurally between two scans it was given — it has no opinion on whether the first scan was ever correct, and it can't tell you a regression happened if nobody ever stored a baseline to compare against. Pairing it with the conformance checks covered in our protocol scan deep-dive covers both halves: conformance catches a broken implementation on day one, and diff catches it breaking again on day two hundred.
Run a baseline scan with Agent Protocol Inspector today, and diff your next deploy against it before you find out from a support ticket instead.
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