crawl4tools

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What is crawl4tools

crawl4tools is a web crawler built on top of the crawl4ai library. It is designed to serve three purposes:

1. An HTTP server, crawl4server, that works directly as an Open WebUI external web loader, returning the body of a URL as Markdown. On the Open WebUI side, this only requires setting Web Loader Engine to external and the External Web Loader URL in the admin UI (or the equivalent WEB_LOADER_ENGINE=external and EXTERNAL_WEB_LOADER_URL environment variables).

2. An MCP server that lets AI agents such as Claude Code fetch the full content of a web page, rather than a summary.

3. A local CLI that downloads a given URL (or multiple URLs at once) as Markdown or other formats.

Related MCP server: cleanfetch

Status

Alpha. This release (0.4.0) provides the local CLI crawl4cli, the MCP server crawl4mcp, and the combined Open WebUI web loader + MCP server crawl4server, with a Dockerfile and compose file. All three commands can show their messages in English or Japanese.

Features

Available now (CLI):

• Download one or more URLs as Markdown, HTML, PDF, screenshot (PNG), MHTML, or the raw source

• PDFs are transcribed to Markdown; images and other non-HTML files are saved as they are

• Clear error messages for HTTP errors, unknown hosts, refused connections, timeouts, and a missing browser

• Downloading through an HTTP/HTTPS/SOCKS5 proxy, with a single retry over a direct connection when the proxy itself fails

• Messages in English or Japanese (see Language of messages)

Available now (MCP server):

• Two tools: fetch returns pages directly to the client as Markdown (default), HTML, or a PNG screenshot (images come back as images, PDFs are transcribed to Markdown); download saves pages in any format (Markdown, HTML, PDF, screenshot, MHTML, or raw) into a directory on the server and returns the paths

• Several URLs per call (default limit 20), fetched concurrently under a server-wide limit (default 3), sharing one headless browser

• stdio (default) and Streamable HTTP transports

• Proxy support with a direct-connection fallback, configured on the server side

• Settings via command-line options, CRAWL4MCP_* environment variables, or a YAML/JSON config file

• Messages in English or Japanese (see Language of messages)

Available now (Open WebUI web loader, crawl4server):

• POST /crawl accepts {"urls": [...]} and returns Markdown plus metadata (source, URL, title, status code, content type) for each page Open WebUI can use; invalid or failing URLs are simply left out of the response instead of failing the whole batch

• Serves the same MCP endpoint as crawl4mcp on a second port, sharing one headless browser and one concurrency limit with the web loader

• GET /health for liveness checks, and an optional bearer API key on the web loader endpoint

• Settings via command-line options, CRAWL4SERVER_* environment variables, or a YAML/JSON config file

• Dockerfile and compose file for running the server in a container

• Messages in English or Japanese (see Language of messages)

Planned:

• Prebuilt Docker image on a registry

• Authentication for the MCP endpoint

• Fallback to a direct connection when SSL bumping by the proxy breaks the result

Installation

The CLI and the MCP server need Python 3.11 or newer and uv.

uv tool install --with-executables-from playwright git+https://github.com/xhighhongo41/crawl4tools
playwright install chromium   # downloads the headless browser (once)

This installs crawl4cli, crawl4mcp, and crawl4server.

The browser is stored in Playwright's cache directory (for example ~/Library/Caches/ms-playwright on macOS). crawl4ai also creates a ~/.crawl4ai directory for its own data.

To run crawl4server in a container instead, see Docker below.

Usage

crawl4cli https://example.com/                    # Markdown to stdout
crawl4cli -o page.md https://example.com/         # save to a file
crawl4cli -d out/ URL1 URL2 URL3                  # several URLs into a directory
crawl4cli -f screenshot https://example.com/      # saves example.com.png
crawl4cli --proxy http://proxy.local:8080 URL     # through a proxy

Only the document goes to stdout; notes, errors, and the summary go to stderr. File names are derived from the URL (https://example.com/a/b → example.com_a_b.md). The exit code is 0 when every URL succeeded, 1 when any failed, and 2 for invalid arguments. Every option can also be set with an environment variable named CRAWL4CLI_<OPTION>, for example CRAWL4CLI_PROXY. The standard HTTP_PROXY/HTTPS_PROXY variables are not used.

Open WebUI web loader (crawl4server)

crawl4server runs a single process that serves both an Open WebUI external web loader and an MCP server, on two separate ports, sharing one headless browser and one concurrency limit (-j) between them.

Running

crawl4server

By default this listens on 127.0.0.1:8766 for the web loader (POST /crawl, GET /health) and 127.0.0.1:8765 for MCP (/mcp).

Connecting Open WebUI

In Open WebUI (0.11.x or later), under Admin Settings > Web Search, set:

• Web Loader Engine: external

• External Web Loader URL: http://<host>:8766/crawl

• External Web Loader API Key: the value passed to --loader-api-key (leave empty if none)

The equivalent environment variables on the Open WebUI side are WEB_LOADER_ENGINE=external, EXTERNAL_WEB_LOADER_URL, and EXTERNAL_WEB_LOADER_API_KEY.

Open WebUI posts {"urls": [...]} to that URL and gets back a JSON array of {"page_content": <Markdown>, "metadata": {"source", "url", "title", "status_code", "content_type"}} documents. URLs that are invalid or fail are simply left out of the response (and logged to the server's stderr), so one bad URL never drops the whole batch. Open WebUI does not time out these requests itself, so tune --timeout and -j/--concurrency if searches feel slow.

Options

Configuration

Settings are resolved in this order: command-line options > CRAWL4SERVER_* environment variables (for example CRAWL4SERVER_LOADER_API_KEY) > config file (--config or CRAWL4SERVER_CONFIG) > built-in defaults. Config file keys are the same option names in snake_case:

host: 0.0.0.0
loader_port: 8766
loader_api_key: change-me
mcp_port: 8765
max_urls: 20
concurrency: 3
lang: ja

Docker

The repository ships a Dockerfile and compose.yaml (no image is published to a registry yet, so build it locally):

git clone https://github.com/xhighhongo41/crawl4tools
cd crawl4tools
mkdir -p downloads
docker compose up -d --build
curl http://localhost:8766/health

Set CRAWL4SERVER_LOADER_API_KEY in compose.yaml's environment section. The container runs as uid 1000, so downloads/ must be writable by it; shm_size: 1gb is set for Chromium. When Open WebUI runs in the same compose project, point it at http://crawl4tools:8766/crawl instead of localhost.

Security

The web loader checks the API key only when --loader-api-key is set; the MCP port has no authentication at all. When listening on a non-loopback host (as in the Docker setup), set a loader API key and do not expose the MCP port beyond a trusted network — crawl4server prints a warning to stderr at startup in that case.

MCP server

crawl4mcp exposes the same fetching engine as an MCP server, with two tools: fetch (return content directly) and download (save it to files). crawl4server (above) serves this same MCP endpoint alongside the Open WebUI web loader, from one process.

Connecting a client

For Claude Code, over stdio (the default transport):

claude mcp add --transport stdio crawl4tools -- crawl4mcp

Or, over Streamable HTTP: start the server, then point Claude Code at it:

crawl4mcp --transport http
claude mcp add --transport http crawl4tools http://127.0.0.1:8765/mcp

For Claude Desktop, add an entry to claude_desktop_config.json:

{
  "mcpServers": {
    "crawl4tools": {
      "command": "crawl4mcp",
      "args": ["--download-dir", "/path/to/downloads"]
    }
  }
}

If Claude Desktop cannot find crawl4mcp (it does not always see your shell's PATH), replace "command": "crawl4mcp" with the full path shown by which crawl4mcp.

Other clients that support the Streamable HTTP transport (for example Open WebUI's MCP support) can connect to http://<host>:<port>/mcp once the server is running with --transport http.

Tools

• urls: one or more http/https URLs, up to the server's per-call limit (--max-urls, default 20); duplicate URLs are fetched once.

• format: for fetch, the page comes back directly as markdown (default), html, or a screenshot (PNG); image URLs are returned as images, and PDFs are transcribed to Markdown. For download, the file is saved as markdown (default), html, pdf, screenshot, mhtml, or raw.

• fit, citations, ignore_links, ignore_images: the same content-shaping options as the CLI's --fit, --citations, --no-links, and --no-images (Markdown only).

• timeout_s: page load timeout for this call, in seconds; defaults to the server's --timeout.

• directory (download only): subdirectory of the server's download directory (--download-dir) to save into; it cannot resolve outside that directory. Defaults to the download directory itself.

When a call covers several URLs, each result starts with a <!-- crawl4tools: url=... status=... --> line; a URL that failed is reported as an error: ... line instead, and the call only fails when every URL fails. A proxy fallback or other remark about a result appears as a <!-- note: ... --> line. download overwrites files that already exist at the destination.

Options

Configuration

Settings are resolved in this order: command-line options > CRAWL4MCP_* environment variables > config file > built-in defaults.

Every option can be set with an environment variable named CRAWL4MCP_ followed by the option's name in upper case with dashes replaced by underscores — for example CRAWL4MCP_MAX_URLS for --max-urls, or CRAWL4MCP_CONCURRENCY for --concurrency. CRAWL4MCP_CONFIG points to the config file itself, same as --config.

The config file is YAML (JSON also works, since JSON is valid YAML), with the same option names as keys, using underscores instead of dashes; unknown keys are an error:

transport: http
host: 127.0.0.1
port: 8765
max_urls: 50
concurrency: 5
download_dir: ./downloads
proxy: http://proxy.local:8080
lang: ja

Relative paths in the config file (such as download_dir) are resolved from the current directory the server is started in.

Security

The Streamable HTTP transport has no authentication. By default the server listens on 127.0.0.1 only; if you bind it to another host, anyone who can reach that port can use the server, and crawl4mcp prints a warning to stderr when it starts. In stdio mode, stdout is reserved for the MCP protocol — all logging goes to stderr.

Language of messages

All three commands can show their messages in English (en) or Japanese (ja).

Choose the language with the --lang option, an environment variable (CRAWL4CLI_LANG, CRAWL4MCP_LANG, CRAWL4SERVER_LANG), or, for the two servers, the lang key in the config file. When more than one is set, the option wins, then the environment variable, then the config file.

Defaults: crawl4cli follows the OS locale (LANGUAGE, LC_ALL, LC_MESSAGES, then LANG, whichever is set first) and uses Japanese when it starts with ja (for example LANG=ja_JP.UTF-8), otherwise English. crawl4mcp and crawl4server always default to English, regardless of the locale, so containers and MCP clients get stable output.

crawl4cli --lang ja https://example.com/
CRAWL4SERVER_LANG=ja crawl4server

This covers --help, error messages, notes and progress lines on stderr, the MCP tools' descriptions and result text, the servers' startup/warning lines, and the web loader's JSON error responses. --help always follows --lang/the environment variable (and, for crawl4cli, the locale) — the config file's lang only applies to messages produced while the server is running.

Always in English, unchanged by --lang: log output; the error:, note:, saved:, done:, failed: line prefixes; JSON keys; the <!-- crawl4tools: url=... status=... --> header lines; GET /health; --version; and anything printed by click or other libraries (for example Usage: or Error: Invalid value ...).

Each process uses one language for its whole run; there is no per-request language.

Acknowledgements

This product includes software developed by UncleCode (https://x.com/unclecode) as part of the Crawl4AI project (https://github.com/unclecode/crawl4ai). Crawl4AI is licensed under the Apache License 2.0.

License

This project is licensed under the Apache License 2.0. See the LICENSE file for details.