mu-webfetch

Plugin that adds a webfetch tool to mu. Fetches the contents of a URL and returns it as markdown — adapted from opencode's webfetch tool.

Originally ported from the webfetch pi-coding-agent extension.

Tool

• webfetch — fetch a URL.
  • url (string, required) — fully-formed http(s) URL.
  • timeout (number, optional) — seconds, capped at 120.
  • Returns the response body. HTML responses are converted to markdown; other text content types are returned as-is. Errors come back as a plain string prefixed with Error:.

Image responses

For image/* responses (excluding image/svg+xml and image/vnd.microsoft.icon) the tool returns a single string of the form:

[image: <mime>, <byteLength> bytes from <url>]
data:<mime>;base64,<base64-payload>

Use sparingly — base64 inlining can blow the model's context window.

Limits

• Size cap: responses larger than 5 MB are rejected (checked against both the content-length header and the actual body length).
• Timeout: default 30 s, max 120 s. Configurable via the timeout parameter.
• Redirects: at most 5 hops; each target is re-validated against the SSRF blocklist.
• Cloudflare retry: a 403 cf-mitigated: challenge response triggers one retry with User-Agent: mu (the first attempt uses a regular browser UA).

Enable it

Add the plugin to your mu config (~/.config/mu/config.json):

{
  "plugins": ["mu-webfetch"]
}

If you publish or install via npm, use "npm:mu-webfetch" instead — the loader will auto-install the package on first run.

Permissioning per agent

Permissions are authored in an agent file's tools: frontmatter map, keyed by tool name (globs supported), with a per-tool decision:

tools:
  webfetch: allow # or `ask` / `deny`

webfetch can only be granted at the whole-tool level — there is no argument-level (per-URL) scoping. Per-argument grants exist only for skill (by skill name) and bash (by command).

Implementation notes

• HTML→markdown conversion uses turndown with script, style, meta, link stripped.
• The first request uses a Chrome-like User-Agent plus a quality-weighted Accept header that prefers markdown when servers offer it.