locc - LLM Output Contract Check

Structured output contract testing for LLM systems. Define what your LLM must output. locc tells you when it drifts.

Install

pip install locc

Quickstart

locc run \
  --contract examples/contract.json \
  --snapshot examples/snapshot.json \
  --output json

What it checks

• Schema conformance: required fields, types, enum values
• Snapshot diff: what changed between runs
• Contract violations: hard constraints your LLM must satisfy

Output

Sample JSON artifact:

{
  "status": "FAIL",
  "checks": [
    {
      "name": "schema_conformance",
      "result": "FAIL",
      "reason": "Missing required field: category"
    }
  ],
  "diff": {
    "category": {
      "expected": "billing",
      "actual": null
    }
  }
}

Exit codes

GitHub Actions

- uses: actions/setup-python@v5
  with:
    python-version: "3.11"
- run: pip install locc
- run: |
    locc run \
      --contract contracts/current.json \
      --snapshot snapshots/current.json \
      --output json > locc_result.json
- uses: actions/upload-artifact@v4
  if: always()
  with:
    name: locc-result
    path: locc_result.json

Stack integration

locc is part of the LLM Reliability Stack. locc output feeds Release Governor for staging-time promotion gating.

License

MIT