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Crawlberg

Crawlberg is a Rust-native web crawler and scraper. It fetches static HTML with reqwest, falls back to headless Chrome when a page needs JS or trips a WAF, and converts every result to clean Markdown via the built-in HTML→Markdown engine.

Use this skill when the user wants to:

• Scrape a single URL to Markdown plus structured metadata.
• Crawl a site following links bounded by depth, page count, and concurrency.
• Enumerate URLs from sitemaps without paying for rendering.
• Drive a real browser (click, type, scroll) and capture the resulting DOM.
• Run the same operations from another agent harness via MCP tools.

Installation

The plugin shells out to a crawlberg binary on PATH. Install one of:

brew install xberg-io/tap/crawlberg
# or build from source:
cargo install crawlberg-cli --features all

The serve and mcp subcommands are gated behind non-default cargo features (api and mcp). The Homebrew tap is built with all features, so both subcommands work out of the box. A from-source build must pass --features mcp (and --features api for serve), or --features all, to include them.

Verify:

crawlberg --version

Headless fallback needs Chrome/Chromium reachable locally (chromiumoxide launches it on demand). Skip the install if you only plan to use --browser-mode never.

Command map

crawlberg scrape <url>          # single page → JSON or Markdown
crawlberg crawl <url...>        # follow links, BFS, depth-bounded
crawlberg map <url>             # enumerate URLs via sitemaps + link extraction
crawlberg interact <url>        # browser actions: click, type, scroll
crawlberg batch-scrape <url...> # scrape many URLs concurrently
crawlberg batch-crawl <url...>  # crawl many seed URLs concurrently
crawlberg download <url>        # download a document, report file metadata
crawlberg citations <input>     # markdown links → numbered citations (text or @file.md)
crawlberg version               # print the crawlberg version as JSON
crawlberg mcp                   # MCP server (stdio) — auto-registered (`mcp` feature)
crawlberg serve                 # REST API server (`api` feature)

crawl also handles batching implicitly: pass multiple seed URLs and it fans out via batch_crawl internally. The explicit batch-scrape and batch-crawl subcommands expose the same concurrency for many independent URLs.

Per-subcommand flags:

Subcommand	Positional	Key flags
scrape	<url>	--proxy, --user-agent (plus shared flags below)
crawl	<url...>	--depth/-d (2), --max-pages/-n, --concurrent/-c (10), --rate-limit (200), --stay-on-domain, --proxy, --user-agent
map	<url>	--limit, --search
interact	<url>	--actions <json> (required)
batch-scrape	<url...>	--concurrent/-c (10), --proxy, --user-agent
batch-crawl	<url...>	--depth/-d (2), --max-pages/-n, --concurrent/-c (10), --rate-limit (200), --stay-on-domain, --proxy, --user-agent
download	<url>	--max-size
citations	<input>	none (input is markdown text or @file.md)
version	—	none
serve	—	--host (0.0.0.0), --port (3000)
mcp	—	none (stdio transport)

Shared flags

Flag	Default	Notes
--format	json	json or markdown.
--timeout	30000	Request timeout in milliseconds.
--browser-mode	auto	auto, always, or never.
--browser-endpoint	—	Optional CDP ws:// or wss:// URL.
--respect-robots-txt	off	Pass to obey robots.txt.
--config <json>	—	Inline JSON or @file.json to override defaults.

The --config flag accepts the full CrawlConfig schema. Anything you set explicitly on the CLI overrides the corresponding JSON field.

These shared flags apply to the crawl/scrape-family subcommands. --format, --browser-mode, --browser-endpoint, and --config cover scrape, crawl, map, interact, batch-scrape, and batch-crawl; download takes --timeout, --browser-mode, --browser-endpoint, --max-size, and --config (no --format). --respect-robots-txt applies to scrape, crawl, map, batch-scrape, and batch-crawl. citations and version take no shared flags.

Scrape a single page

crawlberg scrape https://example.com --format markdown

JSON output (default) carries the rendered Markdown, page metadata (PageMetadata), links by category, images, feeds, JSON-LD blocks, and HTTP response metadata. Use Markdown output when piping into a file the user will read.

See the crawlberg-scraping-html-to-markdown skill for the full flag surface.

Crawl a site

crawlberg crawl https://example.com \
  --depth 3 --max-pages 200 --concurrent 8 --rate-limit 250 \
  --stay-on-domain --respect-robots-txt --format markdown

Crawling is BFS by default, bounded by --depth, --max-pages, and --concurrent. Per-domain politeness is enforced by --rate-limit (milliseconds between requests to the same origin).

See the crawlberg-crawling-a-site skill for the recommended defaults and the full flag surface.

Map URLs

crawlberg map https://example.com --limit 500 --search docs --format markdown

map reads sitemap.xml (and nested sitemaps), then falls back to link extraction from the seed page. It does not render pages — use it to plan a crawl or to feed URLs into another tool.

Browser interaction

crawlberg interact https://example.com \
  --actions '[{"type":"click","selector":"#load-more"},
              {"type":"wait","milliseconds":500},
              {"type":"scrape"}]'

Action types are click, type, press, scroll, wait, screenshot, executeJs, and scrape (to wait for an element, use wait with a selector field). The result wraps the final HTML under interaction.final_html. See the crawlberg-automating-the-browser skill for the full action schema and limits.

MCP server

When this plugin is installed in a Claude Code / Codex / Cursor / Gemini / opencode harness, the MCP server is auto-registered:

crawlberg mcp

mcp is a stdio-transport server and takes no arguments. It requires a binary built with the mcp feature (see Installation).

The server registers nine tools (the same set is served over the Streamable HTTP transport when running crawlberg serve):

Tool	Purpose	Parameters
scrape	Scrape one URL to Markdown or JSON (content, metadata, links).	url (required), format (markdown|json), use_browser (bool — force browser)
crawl	Follow links from a URL, bounded by depth/page count.	url (required), max_depth, max_pages, format, stay_on_domain
map	Discover all URLs via links and sitemaps.	url (required), limit, search, respect_robots_txt
batch_scrape	Scrape multiple URLs concurrently.	urls (required array), format, concurrency
batch_crawl	Crawl multiple seed URLs concurrently.	urls (required array), max_depth, max_pages, format, stay_on_domain, concurrency
download	Download a document and return file metadata.	url (required), max_size
interact	Execute browser actions on a page (mutating/destructive).	url (required), actions (required array of action objects)
generate_citations	Rewrite markdown links as numbered citations + reference list.	markdown (required)
get_version	Return the crawlberg library version.	none

Prefer MCP tools over shelling out when both are available:

• Typed schemas surface argument errors before the call.
• Results stream back as structured tool output instead of stdout text.
• No --format juggling — the harness pulls whatever shape it needs.

Fall back to the CLI when you need to script a pipeline, capture stderr, or chain with shell tools.

Headless fallback

In --browser-mode auto (default), the engine:

1. Fetches statically via reqwest.
2. Detects WAF blocks (8 vendors) and JS-only shells.
3. Re-fetches through headless Chrome with a real fingerprint when needed.

Force the browser path with --browser-mode always when you already know the page needs JS. Use --browser-mode never for hot loops where the cost of a stray Chrome launch is unacceptable.

Point --browser-endpoint ws://host:9222/devtools/browser/<id> at an already-running Chrome to skip the local launch.

See the crawlberg-headless-fallback skill for symptoms, costs, and external-CDP patterns.

Output formats

Mode	Use when
json	Downstream consumer needs metadata, links, images, etc.
markdown	Human reader or LLM-context payload.

Markdown output skips metadata. If you need both, run with --format json and read result.markdown.content.

Robots, rate limits, ethics

• --respect-robots-txt is off by default; pass it for any crawl on a host you do not own.
• The default --rate-limit 200 already produces a polite cadence; raise it for shared hosts.
• Identify the crawler honestly via --user-agent. Do not impersonate a browser unless the operator has approved it.

Cross-references

• crawlberg-crawling-a-site — multi-page crawl with depth, page caps, concurrency, rate limits, and domain scoping.
• crawlberg-scraping-html-to-markdown — single-page rendering, the Markdown output shape, and common pitfalls.
• crawlberg-mapping-urls — map: sitemap + link URL discovery, filtering, and seeding a crawl.
• crawlberg-automating-the-browser — interact: the full scripted action schema, limits, and result shape.
• crawlberg-serving-the-api — serve: the Firecrawl-v1-compatible REST API server and its endpoints.
• crawlberg-headless-fallback — when and how to force the browser backend.