# MCP Inspector review

> MCP Inspector is a developer tool for testing and debugging Model Context Protocol servers through a web UI, CLI, or terminal UI.

Devtoolwatch Board, the week of Oct 25–31, 2026. Canonical page: https://index.devtoolwatch.com/tools/mcp-inspector/

## TL;DR

MCP Inspector is the reference developer tool for testing and debugging MCP servers. It is for developers building or checking MCP servers. One package provides a browser inspector, a scriptable CLI for CI and coding agents, and a terminal UI, all built on one shared core.

## MCP Inspector at a glance

- **Category:** [MCP and agent tools](https://index.devtoolwatch.com/categories/mcp-servers/)
- **Maintained by:** Model Context Protocol (organization, [@modelcontextprotocol](https://github.com/modelcontextprotocol) on GitHub)
- **Language:** TypeScript, JavaScript, CSS
- **Repository:** [github.com/modelcontextprotocol/inspector](https://github.com/modelcontextprotocol/inspector)
- **Website:** [modelcontextprotocol.io/docs/2026-07-28/tools/inspector](https://modelcontextprotocol.io/docs/2026-07-28/tools/inspector)
- **npm package:** [@modelcontextprotocol/inspector](https://www.npmjs.com/package/@modelcontextprotocol/inspector) 2.12.0
- **Latest release:** [2.12.0](https://github.com/modelcontextprotocol/inspector/releases/tag/2.12.0) on GitHub, Oct 21, 2026
- **First published:** Oct 3, 2024

## What MCP Inspector does

- MCP Inspector provides a web client, a Vite + React + Mantine single-page app with a Node backend, for graphical server inspection.
- MCP Inspector includes a scriptable CLI for automation, CI, shell pipelines, and coding agents, with JSON output.
- MCP Inspector offers an interactive terminal UI built with Ink, for when a browser isn't available or wanted.
- MCP Inspector ships mcpdo, an experimental client that connects once and runs many commands through an implicit local daemon.
- MCP Inspector can list a server's tools and call tools with arguments from the command line.
- MCP Inspector handles OAuth tokens, OAuth client secrets, and stdio env values, storing them in the OS keychain by default.
- MCP Inspector supports legacy and modern 2026-07-28 protocol-era negotiation across all clients.

## How to install MCP Inspector

**Web UI with npx**

```
npx @modelcontextprotocol/inspector
```

**CLI with npx**

```
npx @modelcontextprotocol/inspector --cli
```

**TUI with npx**

```
npx @modelcontextprotocol/inspector --tui
```

### Requirements

- Node.js 22.19.0 or newer.
- An OS keychain for encrypted secret storage; otherwise secrets go to ~/.mcp-inspector/secrets.json.

### First steps

1. Launch the web UI against a local stdio server with npx @modelcontextprotocol/inspector node path/to/server/index.js.
2. Open the printed URL, which carries a per-launch API token. Set MCP_AUTO_OPEN_ENABLED=false to stop the browser opening automatically.
3. List a server's tools from the CLI with npx @modelcontextprotocol/inspector --cli node path/to/server/index.js --method tools/list.

## Who MCP Inspector is for

- Developers building MCP servers who want to test and debug them interactively in a browser.
- Teams smoke-testing MCP servers in CI or shell scripts using JSON output and exit codes.
- Coding agents that need fast, machine-readable feedback from MCP servers.
- Developers working in terminals or SSH sessions without a browser, using the TUI.

### Limitations

- MCP Inspector saves secrets unencrypted in ~/.mcp-inspector/secrets.json on machines without a keychain, unless you supply a key.
- MCP Inspector's mcpdo client is experimental.
- MCP Inspector v1 is deprecated and receives security fixes only; moving to v2 changes CLI flags and the Node requirement.
- MCP Inspector releases 2.0.0 through 2.11.0 have three vulnerabilities fixed in 2.12.0.

## Usage data (the week of Oct 25–31, 2026)

- Board rank: #123 overall, #13 in MCP and agent tools, momentum score 58
- Downloads that week: 740.7k (+42% vs 4-week average)
- New GitHub stars per week (last 12 weeks): Aug 9: 52; Aug 16: 59; Aug 23: 69; Aug 30: 49; Sep 6: 47; Sep 13: 43; Sep 20: 54; Sep 27: 50; Oct 4: 55; Oct 11: 46; Oct 18: 56; Oct 25: 61

## MCP Inspector alternatives

| Rank | Tool | Stars | Downloads/wk |
|---|---|---|---|
| #1 | [REA](https://index.devtoolwatch.com/tools/morluto-rea/) | 415.5k | 760.6k |
| #2 | [ha-mcp](https://index.devtoolwatch.com/tools/homeassistant-ai-ha-mcp/) | 5.4k | 118.1k |
| #3 | [Treg](https://index.devtoolwatch.com/tools/superdesigndev-treg/) | 6.9k | 6.7k |
| #4 | [Chrome DevTools MCP](https://index.devtoolwatch.com/tools/chrome-devtools-mcp/) | 54.6k | 2.7M |
| #5 | [codebase-memory-mcp](https://index.devtoolwatch.com/tools/deusdata-codebase-memory-mcp/) | 47.9k | – |
| #6 | [open-computer-use](https://index.devtoolwatch.com/tools/ifuryst-open-computer-use/) | 2.8k | – |

## MCP Inspector FAQ

### Is MCP Inspector free and open source?

MCP Inspector's code is on GitHub (modelcontextprotocol/inspector), but the repository doesn't declare a standard open-source license. Check its license file before using it commercially.

### How do I install MCP Inspector?

Run `npx @modelcontextprotocol/inspector`. It needs Node.js >=22.19.0. The install section above has the other options from the project's README.

### Is MCP Inspector still maintained?

Yes. The modelcontextprotocol/inspector repository was last updated on Oct 21, 2026, and the latest release, 2.12.0 on GitHub, came out on Oct 21, 2026.

### How popular is MCP Inspector?

MCP Inspector has 11.2k GitHub stars as of Nov 1, 2026. It gained 61 new stars in the week of Oct 25–31, 2026, against a 12-week average of 53 a week. Its main package had about 740.7k downloads that week, +42% against its own 4-week average. That made it #13 among MCP servers and agent tools on the Devtoolwatch Board.

### What are the best alternatives to MCP Inspector?

Other MCP servers and agent tools on the Devtoolwatch Board in the week of Oct 25–31, 2026, by momentum: REA (#1), ha-mcp (#2), Treg (#3), Chrome DevTools MCP (#4), codebase-memory-mcp (#5). The alternatives table above has their numbers.

### What is MCP Inspector used for?

MCP Inspector is used for testing and debugging MCP servers. You can connect to a local or remote server, list its tools, call tools, and watch the JSON-RPC exchange in a browser, on the command line, or in a terminal UI.

### Is MCP Inspector an MCP client?

Yes. MCP Inspector provides several clients: a web client, a CLI client, a TUI client, and the experimental mcpdo connection client. They all connect to MCP servers through one shared core.

### How does MCP Inspector work?

MCP Inspector runs through npx. You pass the server's launch command or a remote URL. A single binary dispatches to the web, CLI, or TUI client. All three share transports, configuration files, and OAuth state on disk, so a connection behaves the same in each.

### Where does MCP Inspector store secrets?

MCP Inspector stores OAuth tokens, client secrets, and stdio env values in the OS keychain by default. Without a keychain, such as on headless Linux, SSH sessions, or containers, it saves them to ~/.mcp-inspector/secrets.json, unencrypted unless you supply a key.

## Sources

1. [modelcontextprotocol/inspector on GitHub](https://github.com/modelcontextprotocol/inspector)
2. [MCP Inspector README](https://github.com/modelcontextprotocol/inspector/blob/main/README.md)
3. [@modelcontextprotocol/inspector on npm](https://www.npmjs.com/package/@modelcontextprotocol/inspector)
4. [MCP Inspector website](https://modelcontextprotocol.io/docs/2026-07-28/tools/inspector)
5. [Release 2.12.0 (Oct 21, 2026)](https://github.com/modelcontextprotocol/inspector/releases/tag/2.12.0)
6. [Release 1.0.3 (Oct 21, 2026)](https://github.com/modelcontextprotocol/inspector/releases/tag/1.0.3)
7. [Release 2.11.0 (Oct 14, 2026)](https://github.com/modelcontextprotocol/inspector/releases/tag/2.11.0)
8. [Hacker News: Zero-Touch OAuth for MCP](https://news.ycombinator.com/item?id=48592163)
9. [Hacker News: New MCP Roadmap](https://news.ycombinator.com/item?id=49399591)
10. [Hacker News: MCP Specification – version 2025-06-18 changes](https://news.ycombinator.com/item?id=44314289)
11. [Devtoolwatch Board, the week of Oct 25–31, 2026](https://index.devtoolwatch.com/)