"Tools for Enhancing Browser Functionality or Performance" matching MCP connectors:

Free platform to test MCP clients without installing anything. Create mock tools with dynamic templates, configurable delays, conditions (if/then), and response sequences. Supports JSON-RPC 2.0 over Streamable HTTP. Built-in text_echo and json_echo tools. Rate-limited tiers: anonymous (5 calls/min, 1 mock tool), registered (10 calls/min, 4 mock tools), premium (60 calls/min, unlimited). Zero setup — no install, no registration required. More info: https://www.testmcp.dev

Point Gecko at an OpenAPI spec; get first-call-correct, auth-hidden agent tools.

Apideck Unified API MCP — 330 tools across 200+ SaaS connectors (accounting, CRM, HRIS, ATS).

Create hosted mock REST APIs as tools: seed fake data, import specs, query, write, snapshot. Free.

A webhook inbox for agents: one call returns a live URL. Mock, verify, inspect and replay.

Instant no-signup webhook & HTTP-request inspector for testing webhooks and agent tool-callbacks.

Your DRF API as MCP tools — 1,800 endpoints become 16 dispatchers, permissioned by Django.

Deterministic validation for AI-generated artifacts: JSON Schema, OpenAPI response, SQL syntax.

Discover, pay for, execute, and publish APIs through Apiosk.

Unified gateway exposing 150+ tools across all NexGenData MCP servers via one endpoint.

End-to-end API testing — generate and run tests from OpenAPI, curl, Postman, or real user traffic.

The official MCP Server for the Mux API

An MCP server that provides tools to validate an email address using Dilli Email Validation API.

Swagger Petstore API (v1.0.27) as MCP for testing and prototyping powered by the HAPI MCP server

40+ developer tools from Context7, Code Runner, Python Execute, NPM Sentinel, PlantUML, and Microsoft Learn. Docs lookup, code execution, security scanning. Starts at $0.01/call. Get your API key at app.xpay.sh or xpay.tools

Verify x402 endpoints before payment or publish service profiles for agent discovery.

MCP server and REST API for querying OpenAPI specs. Endpoint-level extraction, schema resolution, 100+ APIs indexed.

Free *.pntr.dev dev subdomains — register subdomains, manage DNS and wildcard records, receive email on disposable inboxes, and capture HTTP requests for webhook debugging. OAuth sign-in; free tier.

Monitor MCP servers, API contracts and AI outputs for schema drift. Alerts on breaking changes.

AI-native mock API server with MCP. Create REST/SOAP mocks from Claude, Cursor, or Windsurf.