Skip to content
SPECIFICTION
Get listed

API Contract Tester

clinetools.com

From $19/mo Free plan Web
Visit clinetools.com
Spec score 8.2 #7 of 22 in Contract Testing Tools

What it is

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.

Spec sheet

Purpose
API Contract Tester verifies frontend-backend API contracts and detects schema mismatches, missing fields, and type incompatibilities.Read 7 Oct 2026 · clinetools.com
Audience
The page describes contract tests as a way for frontend and backend teams to verify that both sides honor an agreed schema.Read 7 Oct 2026 · clinetools.com
Agent integrations
The page gives MCP setup instructions for Cline and Claude Code so an agent can validate contracts automatically.Read 7 Oct 2026 · clinetools.com
CI/CD use
The page says contract tests can run in a deployment pipeline to catch breaking backend changes before the frontend deploys.Read 7 Oct 2026 · clinetools.com
Configuration
On first run, the CLI asks about contract strictness and ignored fields.Read 7 Oct 2026 · clinetools.com
Mismatch detection
It detects missing fields, extra fields, type mismatches, and null violations.Read 7 Oct 2026 · clinetools.com
Reports
It generates detailed mismatch reports with fix suggestions.Read 7 Oct 2026 · clinetools.com
Requirements
The CLI install command is `npx @clinetools/contract-test` and it requires Node.js 18+.Read 7 Oct 2026 · clinetools.com
Schema comparison
It compares an expected TypeScript or OpenAPI schema against actual API responses.Read 7 Oct 2026 · clinetools.com
Security review
ClineTools says every tool undergoes a four-phase security audit.Read 7 Oct 2026 · clinetools.com
Validation
It validates nested objects, arrays, enums, and optional fields.Read 7 Oct 2026 · clinetools.com
Ways to use
Users can try it online by pasting an expected schema and actual response, or run it locally as an MCP server.Read 7 Oct 2026 · clinetools.com

Plans and prices

Free Free forever 100 executions/month · all 42+ core tools · premium modules excluded Read 7 Oct 2026 · clinetools.com
Individual Dev $19 a month 5,000 executions/month · priority support · early access to new tools Read 7 Oct 2026 · clinetools.com
Pro AI Agent $49 a month 50,000 executions/month · team analytics (5 members) · advanced premium modules Read 7 Oct 2026 · clinetools.com
Enterprise $499 a month Unlimited executions · self-hosted deployment · private LLM integration · SLA & dedicated support Read 7 Oct 2026 · clinetools.com

Every API Contract Tester plan and price →

Strong points and limits

Strong points

  • Compares TypeScript, OpenAPI, and JSON contracts
  • Detects missing, extra, and incompatible fields
  • Validates nested structures and optional fields
  • Provides mismatch reports with fix suggestions
  • Supports local MCP and pipeline use

Limits

  • CLI requires Node.js 18 or newer
  • Free plan limits usage to 100 executions monthly
  • Premium modules are excluded from the free plan

Who it suits

It suits frontend and backend teams that need to compare agreed schemas with live responses. It also fits developers using MCP agents or deployment pipelines for contract checks.

Verdict

API Contract Tester focuses on detecting contract drift before it reaches users or deployments. Its free tier supports limited monthly executions, while paid plans add higher allowances and features.

Where Specifiction places it

Alternatives to API Contract TesterAll alternatives →

Pact From $115.42/mo · Free plan 8.7 Visit