API Contract Tester vs Pact Broker

API Contract Tester is a web tool for checking whether frontend and backend APIs follow the same contract. It compares an expected TypeScript, OpenAPI, or JSON schema with actual API responses and identifies missing fields, extra fields, incompatible types, and null violations. Validation covers nested objects, arrays, enums, and optional fields, with mismatch reports that include suggested fixes. You can paste a schema and response into the online interface or run the tool locally as an MCP server. Installation uses `npx @clinetools/contract-test` and requires Node.js 18 or newer. The first CLI run asks about contract strictness and fields to ignore. Setup instructions support Cline and Claude Code, and contract checks can run in deployment pipelines before a frontend release. The free plan costs nothing, billed forever, and includes 100 executions per month; premium modules are excluded. Individual Dev costs $19 a month.

Pact Broker shares consumer-driven contracts and verification results so teams can check compatibility between consumer and provider versions before deployment. It is designed for Pact contracts and also accepts contracts that can be represented as JSON. In a CI workflow, consumer builds publish contracts, provider builds retrieve and verify them, and consumers can use the can-i-deploy command to check whether deployment is safe. The broker includes a REST API, embedded API browser, generated documentation, service network diagrams, verification results and status badges. Webhooks can respond to contract changes by triggering actions such as a provider build or Slack notification. Deployment options documented include Docker and Terraform on AWS; PostgreSQL and SQLite are listed, though SQLite is not supported for long-term operation. Docker images support linux/amd64 and linux/arm64. The open-source self-hosted broker is free, with users responsible for hosting, operation, security, maintenance and upgrades. PactFlow plans are also listed: Starter is free, while Team costs $115.42 a month billed yearly or $127 a month billed monthly.