ContractGate

What ContractGate does

ContractGate exposes ContractGate's semantic data-contract API through MCP. Agents can turn real JSON samples into draft DataContractGate YAML, validate events against an existing contract or inline YAML, deploy versioned contracts, inspect contracts visible to an API key, and review rejected events in quarantine.

The underlying gateway validates more than basic JSON types. Contracts can describe required fields, entities, patterns, enums, glossary terms, and computed metrics. The same validation engine can process inbound events and outbound payloads, making the server relevant to ingestion pipelines, reverse-ETL exports, notebook data, and state sent to decision models.

How it works

The MCP tools call ContractGate HTTP endpoints. infer_contract sends sample events to /contracts/infer and returns a draft without saving it. Reviewers should write the resulting YAML to contracts/<name>.yaml before deployment.

validate_events requires exactly one of contract_id or yaml_content. A contract ID validates through /v1/ingest/{id}; inline YAML uses /playground/validate for each event. Dry-run mode is enabled by default for contract-ID validation, so the request does not create audit, quarantine, or usage records. HTTP 207 and 422 responses are returned as data, allowing an agent to process individual violations and their suggestions.

deploy_contract sends YAML to /contracts/deploy. ContractGate finds or creates the contract by name, makes the submitted version stable, and deprecates the previous stable version. A conflict occurs when the same name and version already exists, so the YAML version must be increased. Deployment is refused while quarantine is pending.

For outbound checks, egress_validate posts to /egress/{contract_id}. Its dry-run default avoids audit and quarantine records. When a response is accepted or repaired, forward response.payload; do not forward the original body after a block or failure.

Setup and configuration

Run the MCP server with npx and the package's latest tag through an MCP client configuration:

{
  "mcpServers": {
    "contractgate": {
      "command": "npx",
      "args": ["-y", "@nightmoose/contractgate-mcp-server"],
      "env": {
        "CONTRACTGATE_API_KEY": "${CONTRACTGATE_API_KEY}"
      }
    }
  }
}

Set CONTRACTGATE_API_KEY to an API key that can access the target ContractGate organization and contracts. The repository also supports a local demo started with make demo; it runs at http://localhost:3000 with authentication disabled and includes starter contracts, a YAML editor, playground, audit log, and event stream.

Tools and capabilities

• Infer draft YAML from sample JSON without persisting it.
• Validate events using a deployed contract or inline YAML.
• Deploy stable contract versions and deprecate earlier stable versions.
• List contracts available to the configured API key.
• Retrieve quarantined events with violation details.
• Validate outbound payloads and return the accepted or repaired payload.

Limitations and notes

Self-hosted free mode is single-organization and does not include API-key authentication, AI inference, quarantine and replay, PII transform rules, or the visual contract builder. Those capabilities are listed for cloud plans. A deployment cannot proceed while quarantine is pending, and an existing name/version combination must be changed before it can be deployed again. LLM output validation is provided by the separate AISchemaGate package rather than by these MCP tools.