Open Data Infrastructure
Agentic Data Contract Tests for Tool Outputs
How contract tests for tool outputs should cover schema, allowed values, freshness, policy state, confidence signals, and replayable evidence.
Agents do not just read data. They ask tools for data, then act like the output is true.
Tool output is data
When an agent calls a tool, the returned object becomes part of the data path. That output may contain facts, permissions, confidence signals, links, summaries, or proposed actions. It needs a contract.
The Model Context Protocol defines tool interfaces. Policy engines can decide what a tool is allowed to return. Lineage and observability systems can record what happened. Contract tests make those pieces concrete before the tool becomes a production dependency.
Contract tests need more than schema
Schema validation is necessary, but it is not enough. A tool output contract should test allowed values, freshness, policy state, owner, source lineage, confidence score, error shape, and redaction behavior. It should also test denial outputs, not only successful responses.
The contract should separate two failures. The tool may fail to answer, or it may answer with data the agent should not trust. Those are different incidents.
Core idea: agentic data contracts treat tool outputs as governed data products, not helper text.
The output should be replayable
Open Data Infrastructure should connect tool output tests to catalogs, policy engines, lineage, and evaluation harnesses. A failed test should say which data product, policy rule, and output field broke the contract.
For adjacent context, read agentic data contracts for tool calls, agentic data replay logs, and MCP and ODI.
What breaks first
- The tool returns valid JSON with stale or unauthorized values.
- Denial responses use a different shape, so agents treat them as normal results.
- Confidence signals are not tested, so low-quality outputs look authoritative.
- Replay requires logs that were never captured with the tool response.
Questions to ask
Ask which fields are contractual, which policies constrain them, and how test fixtures represent success, denial, stale data, and partial failure. Ask whether the output can be replayed from source evidence.
Sources to start with
These primary sources anchor the technical claims in this guide.
- Model Context Protocol tools specification
- Open Policy Agent policy language documentation
- OpenLineage object model documentation
- OpenTelemetry logs specification
A tool output is safe when the contract can prove why the agent should believe it.