inspector
MCP ServerFreeVisual testing tool for MCP servers
Capabilities12 decomposed
mcp server protocol bridging via express proxy
Medium confidenceTranslates browser-incompatible MCP transport protocols (STDIO, SSE, Streamable HTTP) into browser-friendly transports (SSE, WebSocket) through an Express-based proxy server. The mcpProxy function maintains bidirectional message routing between transportToClient and transportToServer, enabling browsers to interact with local and remote MCP servers without direct process spawning or long-lived pipe management.
Uses MCP SDK's transport abstraction layer to dynamically support STDIO, SSE, and Streamable HTTP without hardcoding transport-specific logic, enabling single proxy to handle heterogeneous server implementations. Session token generation at startup provides lightweight security without external auth infrastructure.
More flexible than custom STDIO wrappers because it abstracts transport selection and supports remote servers via SSE/HTTP, not just local processes.
interactive web ui for mcp tool discovery and execution
Medium confidenceReact-based web interface (built with Radix UI and Vite) that dynamically renders MCP server capabilities including tools, resources, and prompts. The UI introspects server metadata, generates forms for tool parameters, executes tools via the proxy, and displays results with full protocol visibility. Connection management hooks (useConnection) maintain WebSocket/SSE state and handle reconnection logic.
Dynamically generates parameter forms from MCP tool schemas using Radix UI components, enabling zero-configuration testing of arbitrary MCP servers. useConnection hook manages transport state and reconnection without requiring manual connection lifecycle management.
More user-friendly than curl/CLI testing because it auto-generates forms from schemas and provides visual feedback; more accessible than writing custom client code.
monorepo workspace management with npm workspaces
Medium confidenceOrganizes inspector into three interdependent npm packages (inspector-client, inspector-server, inspector-cli) using npm workspaces. Shared dependencies are hoisted to root package.json, reducing duplication and ensuring version consistency. Build scripts coordinate compilation across packages (TypeScript → JavaScript), and development scripts enable simultaneous development of all packages with hot-reload support via Vite.
Uses npm workspaces to manage three tightly-coupled packages (client, server, CLI) with shared dependencies hoisted to root, reducing duplication and ensuring version consistency. Vite dev server enables simultaneous development with hot-reload.
More maintainable than separate repositories because shared dependencies are centralized; more flexible than a single package because each component can be deployed independently.
typescript compilation with vite bundling for web client
Medium confidenceCompiles TypeScript source code to JavaScript using TypeScript compiler, then bundles the web client using Vite for development and production builds. Vite provides hot module replacement (HMR) during development, enabling instant feedback on code changes without full page reloads. Production builds are minified and optimized for browser delivery. Build configuration is defined in vite.config.ts with React plugin for JSX support.
Uses Vite for development (with HMR) and production bundling, providing fast iteration during development and optimized builds for deployment. TypeScript compilation is integrated into Vite pipeline, eliminating separate build step.
Faster development iteration than Webpack because Vite uses native ES modules; smaller production bundles than Create React App because Vite optimizes aggressively.
multi-transport mcp client with dynamic transport selection
Medium confidenceAbstracts MCP transport selection (STDIO, SSE, Streamable HTTP) behind a unified client interface using the MCP SDK's transport layer. The proxy server dynamically instantiates the correct transport based on user configuration, enabling seamless switching between local executable servers, remote SSE endpoints, and HTTP-based servers without code changes. Transport initialization is lazy-loaded on first connection.
Leverages MCP SDK's transport abstraction to support STDIO, SSE, and Streamable HTTP from a single proxy without transport-specific branching logic. Transport selection is configuration-driven, not code-driven, enabling runtime switching.
More flexible than transport-specific clients because it abstracts protocol differences; more maintainable than custom transport wrappers because it uses official SDK implementations.
session-based authentication with random token generation
Medium confidenceGenerates a cryptographically random session token at proxy startup and validates it on every request via environment variable (MCP_PROXY_AUTH_TOKEN) or URL parameter. Token is not persisted across restarts, preventing unauthorized access to local process execution. Validation occurs before any MCP protocol message is routed, providing a lightweight security boundary without external auth infrastructure.
Uses random token generation at startup rather than persistent credentials, making it suitable for ephemeral development environments. Token validation is enforced before proxy initialization, preventing unauthorized process spawning.
Simpler than OAuth/SAML for local development but less suitable for production; more secure than no authentication because it prevents accidental exposure to other processes.
command-line interface for programmatic mcp server interaction
Medium confidenceCommander.js-based CLI tool (@modelcontextprotocol/inspector-cli) that enables non-interactive, programmatic interaction with MCP servers. Supports transport configuration via CLI flags, tool execution with JSON parameter input, and structured output for scripting. CLI client methods wrap MCP SDK calls, enabling integration into CI/CD pipelines, automation scripts, and headless testing frameworks without requiring a web browser.
Provides CLI wrapper around MCP SDK client methods, enabling headless testing without web UI. Each invocation is stateless, making it suitable for CI/CD pipelines and containerized environments.
More suitable for automation than web UI because it's scriptable and doesn't require browser; more accessible than raw SDK usage because CLI abstracts transport configuration.
real-time protocol message logging and inspection
Medium confidenceCaptures and displays all MCP protocol messages (JSON-RPC 2.0 requests and responses) flowing through the proxy in real-time. Messages are logged with timestamps, method names, parameters, and results. The web UI displays logs in a scrollable panel with syntax highlighting, enabling developers to inspect protocol details without external tools like Wireshark. Logs are stored in browser memory (no persistence across page reloads).
Intercepts all MCP protocol messages at the proxy layer before they reach the browser, providing complete visibility into bidirectional communication. Logs are rendered in the web UI with syntax highlighting, eliminating need for external protocol analyzers.
More convenient than Wireshark or tcpdump because it's integrated into the inspector UI and understands MCP protocol structure; more complete than server-side logging because it captures both directions.
resource and prompt metadata introspection
Medium confidenceDynamically discovers and displays MCP server resources (files, documents, data sources) and prompts (reusable instruction templates) alongside tools. The web UI renders resource listings with descriptions and access patterns, and prompt templates with parameter placeholders. Introspection queries the server's resource and prompt endpoints on connection, populating the UI without requiring manual configuration or documentation lookup.
Automatically discovers and renders resources and prompts from server metadata without hardcoding or manual configuration. UI treats resources and prompts as first-class citizens alongside tools, providing unified capability exploration.
More discoverable than documentation because it's dynamic and always in sync with server; more complete than tool-only inspection because it includes resources and prompts.
draggable ui components for parameter composition
Medium confidenceReact-based drag-and-drop interface for composing tool parameters and building complex inputs. Supports reordering parameters, nesting objects, and constructing arrays through visual interactions. Draggable components use React state management to track parameter changes in real-time, enabling visual parameter building without manual JSON editing. Generated parameter objects are validated against tool schemas before execution.
Implements drag-and-drop parameter composition using React state, eliminating need for manual JSON editing. Real-time validation against tool schemas provides immediate feedback on parameter correctness.
More user-friendly than JSON editing because it's visual; more flexible than form-only input because it supports arbitrary nesting and reordering.
connection state management with automatic reconnection
Medium confidenceuseConnection React hook manages WebSocket/SSE connection lifecycle, including initial connection, disconnection handling, and automatic reconnection with exponential backoff. Hook maintains connection state (connected, disconnected, reconnecting) and exposes methods for sending messages and subscribing to connection events. Reconnection logic retries with increasing delays (1s, 2s, 4s, 8s, etc.) up to a maximum, preventing connection storms.
Implements exponential backoff reconnection logic within a React hook, eliminating boilerplate connection management code. Hook exposes connection state and events, enabling UI to react to connection changes without manual polling.
More resilient than simple WebSocket because it includes automatic reconnection; more maintainable than custom connection logic because it's encapsulated in a reusable hook.
tool execution with parameter validation and error handling
Medium confidenceExecutes MCP tools by sending JSON-RPC 2.0 requests through the proxy, validating parameters against tool schemas before execution. Handles tool responses (results or errors) and displays them in the UI with formatted output. Error handling distinguishes between schema validation errors (caught before execution), protocol errors (MCP-level failures), and execution errors (tool-specific failures), providing detailed error messages for each type.
Validates parameters against tool schemas before sending to server, catching errors early and providing immediate feedback. Error handling distinguishes between validation, protocol, and execution errors, enabling precise debugging.
More robust than raw JSON-RPC because it includes schema validation; more user-friendly than CLI because it provides formatted output and visual error messages.
Capabilities are decomposed by AI analysis. Each maps to specific user intents and improves with match feedback.
Related Artifactssharing capabilities
Artifacts that share capabilities with inspector, ranked by overlap. Discovered automatically through the match graph.
@modelcontextprotocol/express
Express adapters for the Model Context Protocol TypeScript server SDK - Express middleware
OpenMCP Client
** - An all-in-one vscode/trae/cursor plugin for MCP server debugging. [Document](https://kirigaya.cn/openmcp/) & [OpenMCP SDK](https://kirigaya.cn/openmcp/sdk-tutorial/).
@cloudflare/mcp-server-cloudflare
MCP server for interacting with Cloudflare API
Plugged.in
** - A comprehensive proxy that combines multiple MCP servers into a single MCP. It provides discovery and management of tools, prompts, resources, and templates across servers, plus a playground for debugging when building MCP servers.
mcp-server
mcp server
decocms
Deco CMS — Self-hostable MCP Gateway for managing AI connections and tools
Best For
- ✓MCP server developers testing servers locally via web UI
- ✓Teams building MCP integrations who need visual debugging
- ✓Developers working with heterogeneous MCP transport implementations
- ✓MCP server developers validating tool definitions and parameter schemas
- ✓Non-technical stakeholders exploring server capabilities via visual interface
- ✓QA engineers testing MCP servers without writing client code
- ✓Inspector maintainers managing multiple interdependent packages
- ✓Teams building tools with web UI, server, and CLI components
Known Limitations
- ⚠Proxy adds network latency for STDIO-based servers (typically 10-50ms per round-trip)
- ⚠Session token authentication is random per startup — no persistent credentials across restarts
- ⚠WebSocket transport requires browser support; SSE fallback may have higher latency
- ⚠No built-in load balancing for multiple concurrent MCP server connections
- ⚠UI rendering performance degrades with >100 tools in a single server (no virtualization implemented)
- ⚠Form generation relies on JSON Schema compliance — non-standard schemas may render incorrectly
Requirements
Input / Output
UnfragileRank
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Repository Details
Last commit: Apr 22, 2026
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Visual testing tool for MCP servers
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