API Contract Tester vs Specmatic

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.

Specmatic turns API specifications into executable contracts for designing, building, and governing APIs. Its suite includes Genie, which generates API specifications from plain English; Studio for visual API workflows and contract testing; and Insights for API governance and analytics. Listed formats include OpenAPI, AsyncAPI, Avro, GraphQL SDL, Protobuf, WSDL, and Arazzo. Protocols include HTTP/REST, Kafka, gRPC, GraphQL, Google Pub/Sub, JMS, MQTT, RabbitMQ, SOAP, WebSocket, and MCP. The free Open Source plan includes contract and API resilience testing, service virtualization, backward compatibility testing, a proxy server, and a specification coverage report. Enterprise adds Studio and Insights, available as SaaS or on-premise, alongside additional protocol and workflow capabilities. The software supports Linux, macOS, Windows, and self-hosted environments, with installation options including shell and PowerShell scripts, npm, and pip. A free plan is available; the pricing note lists paid access from $10/user/mo (annual).