MQTT Specification

mqtt-spec-mcp

An offline Model Context Protocol server for searching and citing the OASIS MQTT 3.1.1 and MQTT 5.0 specifications. Agents get focused source excerpts instead of loading a whole specification.

• Four read-only tools for search, section retrieval, outlines, and exact lookups.
• Bundled indexes: no network, database, embeddings, or LLM at query time.
• Explicit version selection on every call; no default or cross-version results.
• Bounded section pages and compact search evidence packs with source links.

The server retrieves evidence; the agent does the reasoning. OASIS publications remain authoritative, and retrieved excerpts are not a guarantee of a correct answer.

Setup

Your MCP client starts the server on your machine and talks to it over stdio. There is no separate install step: configure the client to run uvx mqtt-spec-mcp, and uv downloads the package from PyPI the first time, caches it, and starts it. uv also fetches a compatible Python (3.10 or newer) if you don't have one. Each time the client starts the server, uv checks PyPI for a newer release, so updates arrive automatically.

1. Install uv.
2. Add the server to your client, as shown below. The server needs no environment variables, configuration files, or flags.

The server is also listed in the MCP Registry as io.github.cartertinney/mqtt-spec-mcp, for clients that install from it.

Claude Code, Codex, GitHub Copilot CLI, and Gemini CLI

Each of these adds the server for all your projects with one command:

claude mcp add --scope user mqtt-spec -- uvx mqtt-spec-mcp   # Claude Code
codex mcp add mqtt-spec -- uvx mqtt-spec-mcp                 # OpenAI Codex CLI and IDE extension
copilot mcp add mqtt-spec -- uvx mqtt-spec-mcp               # GitHub Copilot CLI
gemini mcp add --scope user mqtt-spec uvx mqtt-spec-mcp      # Gemini CLI

VS Code (GitHub Copilot)

Add the server to your user profile from a terminal:

code --add-mcp '{"name":"mqtt-spec","type":"stdio","command":"uvx","args":["mqtt-spec-mcp"]}'

Or run MCP: Add Server from the Command Palette, or add it to one project's .vscode/mcp.json:

{
  "servers": {
    "mqtt-spec": {
      "type": "stdio",
      "command": "uvx",
      "args": ["mqtt-spec-mcp"]
    }
  }
}

Claude Desktop, Cursor, and other clients

Most other clients read the same mcpServers entry:

{
  "mcpServers": {
    "mqtt-spec": {
      "command": "uvx",
      "args": ["mqtt-spec-mcp"]
    }
  }
}

• Claude Desktop: Settings → Developer → Edit Config opens claude_desktop_config.json. Quit and reopen Claude after saving.
• Cursor: use ~/.cursor/mcp.json for all projects, or .cursor/mcp.json in one project.
• Zed: put the same entry under context_servers in its settings file.

ChatGPT and the OpenAI Agents SDK

ChatGPT connects only to remote MCP servers over HTTPS, so it can't start this local server; use the Codex CLI or IDE extension instead (above). In an agent built with the OpenAI Agents SDK, connect with MCPServerStdio(params={"command": "uvx", "args": ["mqtt-spec-mcp"]}).

Without uv

Install the package with pipx install mqtt-spec-mcp, or with pip install mqtt-spec-mcp in a Python 3.10+ environment. Then configure your client to run the command mqtt-spec-mcp, with no arguments, instead of uvx mqtt-spec-mcp.

Troubleshooting and upgrades

• The client can't find uvx. Desktop apps often don't see your shell's PATH. Use the absolute path printed by which uvx (macOS and Linux) or where uvx (Windows).
• The first start times out. The first launch downloads the package, which can take a few seconds. Download it ahead of time with uvx --from mqtt-spec-mcp python -c pass.
• Updates. A new release is used from the next time your client starts the server. uv reuses PyPI's answer for up to 10 minutes, so a release can take that long to appear. After an update, start a new conversation so the client drops cached tool schemas. To stay on one version, use [email protected] in place of mqtt-spec-mcp in the client's arguments.
• No network access. The server works offline, but starting it with uvx needs to reach PyPI unless uv checked within the last 10 minutes. To run without network access, install it once with uv tool install mqtt-spec-mcp and configure the client to run mqtt-spec-mcp. uvx mqtt-spec-mcp then runs the installed copy as well, and updates come only from uv tool upgrade mqtt-spec-mcp.

Tools

Every call requires version: exactly "3.1.1" or "5.0".

Tool	Use
mqtt_spec_search	Find excerpts by key terms, section id, or requirement label.
mqtt_spec_get	Read a section, with bounded pages and continuation cursors.
mqtt_spec_outline	Browse section ids and titles without body text.
mqtt_spec_lookup	Look up packets, properties, codes, requirements, or glossary terms.

Example tool arguments:

{"version": "5.0", "query": "Receive Maximum default; QoS 0 Receive Maximum"}

Use that with mqtt_spec_search. For an exact lookup with mqtt_spec_lookup:

{"version": "3.1.1", "kind": "return_code", "query": "0x80", "packet": "SUBACK"}

The latter returns Failure. The same value in MQTT 5.0 is Unspecified error: version-specific labels and codes must not be carried between versions.

Guidance for agents

1. Ask which MQTT version the user means if they have not specified one.
2. Look up an exact entity, or search with the question's key terms. Separate parts of a question with ;.
3. Answer from the evidence, preserving MUST/SHOULD/MAY and their conditions. Cite the version and section beside each claim.
4. Search excerpts can omit exceptions. Before claiming silence, optionality, or no exception, fetch the deciding section if it is excerpted or absent. The server recommends at most one fetch and one repeat search per version.
5. For comparisons, query each version separately. A miss in one says nothing about the other.

See the tool reference for all parameters, pagination, result formats, and errors.

Sources and limitations

Version	Indexed publication
3.1.1	MQTT Version 3.1.1 Plus Errata 01, 10 December 2015
5.0	MQTT Version 5.0, 7 March 2019

Indexes are generated from pinned source documents and validated at startup. They are transformed retrieval aids, not official publications. MQTT 3.1 (pre-OASIS) is not supported, and this is not a broker or a conformance validator.

Limitations and roadmap describe known retrieval gaps. Benchmarks covers the offline regression checks and reports from historical agent evaluations. Those evaluations used a private harness, corpus, and raw runs, so they cannot be reproduced from this repository.

Development

See development and release checks for running from a checkout, testing, rebuilding indexes, and releasing. Benchmark checks are checkout-only and are not shipped with the server.

License

The code is MIT licensed. Specification text in the indexes and returned excerpts is copyright OASIS Open, not MIT licensed. NOTICE contains the source attribution, transformation details, and OASIS notices.