steam-debug

steam-debug

A Claude skill and standalone CLI for inspecting, debugging, and injecting code into a running Steam client — desktop or Steam Deck — via the Chrome DevTools Protocol (CDP).

Steam's UI is a Chromium Embedded Framework (CEF) app. Launched with debug flags it exposes the same protocol browser DevTools uses, so the entire Steam UI can be inspected and modified at runtime like a web page. steam-debug.mjs wraps that protocol into focused commands — read React state, search webpack modules, resolve minified class names, inspect computed CSS, drive navigation, stream logs, and inject custom CSS/JS.

Built for plugin, theme, and integration development against Steam's UI.

Works on desktop and Steam Deck. Same commands for both — a desktop client on macOS, Linux or Windows, and a Deck over the network via --host. Both are exercised by the test suite, and any command can run against both at once. See reference/remote.md.

Scope. This is a debugging and development tool. Injection is per-session and disappears on reload, by design — it exists so you can try a change and see what happens.

Out of scope: making a change persist or load on startup, packaging or distributing plugins, and anything that runs unattended inside someone's client. That belongs in a plugin loader. The boundary is simple — this helps you find out what is going on and try a change; making a change stick is someone else's job.

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Using with Claude

Place this directory at ~/.claude/skills/steam-debug/. Claude Code discovers it via SKILL.md.

Describe the task in plain language; Claude selects the commands, interprets output, and follows the operating procedure in SKILL.md:

"Why is my injected CSS not showing up in Big Picture Mode?" "Find the webpack module that defines the DialogButton component." "Make the Quick Access Menu background darker." "Something is throwing a React error on the downloads page — find it."

SKILL.md is a strict SOP rather than a tutorial: it gates work behind a preflight check, fixes which commands may be used, and defines how to verify a result before reporting it — because the easiest mistake here is a confident answer drawn from the wrong window, a stale route, or a style that computed but never painted.

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Requirements

• Node.js 22+ — uses built-in WebSocket and fetch, no dependencies
• A Steam client with CDP enabled — either:
  • desktop, launched with -cef-enable-debugging (see below), or
  • a Steam Deck with Settings → System → Developer → CEF Remote Debugging, reachable on your network. Address it with --host; SteamOS serves CDP on port 8081.
• Chrome — optional, only for the interactive DevTools UI

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Launch Steam in debug mode

Launch flags are read only at startup. A already-running instance silently ignores them, so it must be closed first — note that this drops in-progress downloads and running games.

# macOS
pkill -f Steam
# Linux
pkill steam
# Windows
taskkill /IM steam.exe /F

Omit -gamepadui to debug the classic desktop UI, which is a different front end.

curl http://localhost:8080/json/version   # {"Browser": "Chrome/...", ...}

Steam takes 30–90 seconds to fully initialise. Poll status until both marks are ✓.

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Usage

S=~/.claude/skills/steam-debug/steam-debug.mjs

node $S status
node $S help

--json works on every command and guarantees machine-readable stdout, so nothing has to be parsed out of prose. logs --json emits one JSON object per line.

Credentials are redacted by default. Any JSON value under a key that looks like a token, password, Steam Guard blob, machine ID or session id is replaced with a description of what was withheld, and eval refuses an expression touching SteamClient.Auth. Pass --show-secrets when you are deliberately debugging sign-in.

--host takes a list, so any command can run against a desktop client and a Steam Deck together — the practical way to check a plugin behaves the same on both:

node $S page --host localhost,steamdeck
node $S inject css theme.css --host localhost,steamdeck --target BigPicture
node $S logs --host localhost,steamdeck --level error   # concurrent, tagged per device

Output is labelled per device, --json aggregates into { devices: [...] }, --out is suffixed so captures do not overwrite, and the exit code is 0 only if every device succeeded.

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Reading Steam's own logs

Three streams, not o