Build, validate, and sign a .mcpb MCP bundle with the mcpb CLI

Documented steps

1. Know the format: an .mcpb file is a zip archive containing a local MCP server plus a manifest.json describing it — conceptually like a .crx or .vsix. The project was renamed from DXT/Desktop Extensions to MCPB; the CLI is now `mcpb` and files are .mcpb. Ref: https://github.com/anthropics/mcpb
2. Install the CLI: `npm install -g @anthropic-ai/mcpb` (or invoke via npx).
3. Scaffold the manifest: `mcpb init` in the server directory. Required manifest fields are manifest_version, name, version, description, author (object with required name), and server.
4. Fill in the server block: {"type": "node"|"python"|"binary"|"uv", "entry_point": "server/index.js", "mcp_config": {"command": "node", "args": ["${__dirname}/server/index.js"], "env": {"API_KEY": "${user_config.api_key}"}}}. Use platform_overrides for win32/darwin/linux differences.
5. Declare anything the user must supply in `user_config`: each field takes type (string|number|boolean|directory|file), title, description, required, default, and — for secrets — sensitive: true so the host masks and stores it securely. Use multiple: true for repeatable directory/file inputs; the array expands into separate CLI args.
6. Vendor the runtime dependencies into the bundle: Node — `npm ci --production` and ship node_modules/; Python (traditional) — vendor into server/lib/ and set PYTHONPATH via mcp_config.env; uv type — ship pyproject.toml and do NOT include server/lib or server/venv.
7. Trim the archive with a .mcpbignore (gitignore-style). pack already excludes .git/, .DS_Store, *.log, .env.local, package-lock.json, yarn.lock, node_modules/.cache, node_modules/.bin, *.map and similar.
8. Validate then pack: `mcpb validate manifest.json` and `mcpb pack . my-server.mcpb`. Inspect the result with `mcpb info my-server.mcpb`.
9. Sign for distribution: `mcpb sign my-server.mcpb --cert cert.pem --key key.pem` (add --intermediate for a chain, or --self-signed for development). Check it with `mcpb verify my-server.mcpb`; `mcpb unsign` strips a signature.