MCP & Protocol Testing / Scenario
The Tool Contract Audit
A shipped MCP server passes its own happy-path tests but breaks real agents. Read the schema, the call log, and the results, then find every contract hole.
- Difficulty
- Hard
- Format
- Scenario
- Points
- 200
- Estimate
- 16 min
// MISSION BRIEF
Your Mission
You inherit an MCP server whose create_ticket tool is behaving strangely for downstream agents. The team says "it works, look, the demo call succeeds." You have the tool definition, a batch of real calls, and the responses.
Audit the contract. The bug is not in one place, it is in the gap between what the schema promises and what the server does.
// FIRST CONTACT
Battle teaser
First artifact
tools/list -> create_ticket definition
Which contract violations are visible in the call log? (Select all that apply.)
- ACall B: a missing required field ('priority') was accepted instead of rejected
- BCall A: a valid call succeeded (this is correct behavior)
- CCall C: an out-of-enum value ('URGENT') was accepted and stored
- DCall D: a downstream 503 was reported as a success (should be isError: true)
Answers, scoring, hints, and the full battle stay sealed.
// SKILL TAGS
mcpcontract-testingtoolsjson-schemaerror-handling