Chrome CDP

Lightweight Chrome DevTools Protocol CLI. Connects directly via WebSocket — no Puppeteer, works with 100+ tabs, instant connection. Uses a persistent per-tab daemon so Chrome's "Allow debugging" modal fires only once.

Prerequisites

• Chrome with remote debugging enabled: open chrome://inspect/#remote-debugging and toggle the switch
• Python 3.10+ with websockets library

Commands

All commands use python -m chrome_cdp. The <target> is a unique targetId prefix from list; copy the full prefix shown in the list output (for example 6BE827FA). The CLI rejects ambiguous prefixes.

List open pages

python -m chrome_cdp list

Take a screenshot

python -m chrome_cdp shot <target> [file]    # default: /tmp/screenshot.png

Captures the viewport only. Scroll first with eval if you need content below the fold. Output includes the page's DPR and coordinate conversion hint (see references/coordinate-system.md).

Accessibility tree snapshot

python -m chrome_cdp snap <target>

Prefer snap over html for understanding page structure — it's compact and semantic.

Evaluate JavaScript

python -m chrome_cdp eval <target> <expr>

Watch out: avoid index-based selection (querySelectorAll(...)[i]) across multiple eval calls when the DOM can change between them (e.g. after clicking Ignore, card indices shift). Collect all data in one eval or use stable selectors.

Other commands

python -m chrome_cdp html    <target> [selector]   # full page or element HTML
python -m chrome_cdp nav     <target> <url>         # navigate and wait for load
python -m chrome_cdp net     <target>               # resource timing entries
python -m chrome_cdp click   <target> <selector>    # click element by CSS selector
python -m chrome_cdp clickxy <target> <x> <y>       # click at CSS pixel coords
python -m chrome_cdp type    <target> <text>         # Input.insertText at current focus
python -m chrome_cdp loadall <target> <selector> [ms]  # click "load more" until gone
python -m chrome_cdp evalraw <target> <method> [json]  # raw CDP command passthrough
python -m chrome_cdp stop    [target]               # stop daemon(s)

Coordinates

shot saves an image at native resolution: image pixels = CSS pixels x DPR. CDP Input events (clickxy etc.) take CSS pixels.

CSS px = screenshot image px / DPR

shot prints the DPR for the current page. Typical Retina (DPR=2): divide screenshot coords by 2.

For the full coordinate system reference including DPR detection, viewer scaling, and worked examples, see references/coordinate-system.md.

Tips

• Prefer snap over html for page structure — it's compact and semantic.
• Use type (not eval) to enter text in cross-origin iframes — use click/clickxy to focus first, then type.
• Chrome shows an "Allow debugging" modal once per tab on first access. A background daemon keeps the session alive so subsequent commands need no further approval. Daemons auto-exit after 20 minutes of inactivity.
• Use evalraw to send arbitrary CDP methods not covered by the built-in commands (e.g. DOM.getDocument, Network.enable).

Advanced Usage

For detailed protocol documentation, see:

• references/coordinate-system.md — DPR, CSS pixels, screenshot coordinate mapping
• references/daemon-ipc.md — Unix socket protocol, NDJSON format, request/response schema