Web Browser

Environment-aware browser operations skill. Detects the runtime environment and routes to the appropriate browser backend, then runs one of two workflows: UI testing/verification (ui-test) or browser-login-assisted credential issuance (credential-issue).

Topics

Topic	Description	Guide
ui-test	Snapshot analysis, click/fill/verify, page-state diagnosis	ui-test.md
cdp-trace	CDP-based closed shadow DOM cascade diagnosis (DOM.getDocument pierce:true + CSS.getMatchedStylesForNode)	cdp-trace.md
credential-issue	service+command param → open login screen → wait for user login → issue access key/token/secret → hand off to automation	credential-issue.md

Topic Dependencies

web-browser (Step 0: environment detection — shared by all topics)
  ├─→ ui-test (UI verification)
  │     └─→ cdp-trace (extends ui-test for closed shadow DOM)
  └─→ credential-issue (browser-login-assisted token/key issuance)
        └─→ chrome-devtools backend preferred (reuses the user's real logged-in session)

• Step 0 (below) is shared — every topic detects the backend first, then runs its workflow.
• ui-test, cdp-trace are the UI-testing family.
• credential-issue reuses the same backend routing + the user-visibility rule, generalized into a service+command parameterized auth flow.
• Authentik SSO verification (sso-verify) is not included in this skill — it remains in a separate local-only sso-verify skill (user-environment specific, untracked).

CRITICAL — user visibility is the top priority (HARD STOP)

The primary purpose of browser diagnosis/verification is "the user sees it on their own screen". Screenshot capture is supporting evidence, not a substitute for visibility.

#	Don't	Do
1	Launch with chromium.launch({ headless: true }) and only attach a screenshot in chat	chromium.launch({ headless: false, slowMo: 500 }) — let the user follow in real time
2	"I showed the user a screenshot, so it's fine"	screenshot ≠ visible to the user. If the user says "show me", open a visible browser + slowMo
3	wmux/cmux/Playwright MCP disconnected → fall back to headless CLI	Even on CLI fallback, force headless: false. On a Windows desktop OS, a chromium GUI is available
4	"headless is faster and more stable by default" mindset	Speed costs user visibility. If the user says "show me", visibility wins
5	Playwright MCP disconnected → CLI fallback auto-selects headless	CLI fallback is also headless: false. headless is only for explicit non-interactive cases (e.g., CI assertion)
6	SaaS/API task lacks credentials → fallback to manual user UI operation	Do NOT recommend manual user UI clicking when API access is available; fallback to credential-issue topic to issue token/key first

API-capable environment without credentials — fallback to credential-issue (HARD STOP)

When a task can be performed via API (e.g., Google Forms API, GitHub API, AWS API), but required API tokens or access keys are missing in the environment, do NOT recommend manual user UI clicking or surrender to direct manual UI operation. You MUST recommend credential-issue topic to issue the access key/token via browser login first, then proceed with backend API automation.

#	Don't	Do
1	API token missing → "Please edit/click manually on the website"	Recommend credential-issue topic to issue API token/key via browser login
2	Direct UI automation fails → fallback to manual user operation	Check if API automation is available → issue credential via credential-issue → execute API

Self-check (every time before launching Playwright/chromium)

1. Did the user use a visibility request keyword such as "show me", "open it", "web-browser", or "browser test"? → If yes, force headless: false
2. Is this work interactive verification or diagnosis for the user? → If yes, headless: false
3. headless is justified only when (a) CI assertion (b) the user explicitly said "in headless" (c) Playwright MCP is used (the UI shows itself)
4. screenshot is supporting evidence — it can be attached to a chat report, but it does not replace user visibility

Violation case (2026-05-28, 1st)

During a closed shadow DOM ak-library cascade investigation, used a npx playwright Bash invocation + chromium.launch({ headless: true }) and only attached a screenshot in chat. The user requested "show it via web-ui-test" and no visible browser was provided. The user reacted angrily that the Chromium UI never appeared.

Login wall mid-capture — ask before stopping, don't silently defer (HARD STOP)

When a capture/documentation task (report evidence, purchase/registration flow guide, etc.) hits a screen that requires login, and completing that login would reveal materially different information than what's already captured (e.g., the real final price vs. a promotional pre-login price, actual post-login UI state vs. an assumption), do NOT silently stop and paper over the gap with a deferral disclaimer. Ask the user via AskUserQuestion whether to continue (via interactive login in a visible backend) or whether the pre-login capture is sufficient for the purpose at hand.

#	Don't	Do
1	Hit a login wall → write "please have finance/ops enter payment details themselves for security" and stop, without asking	Decompose the remaining flow: payment/credential entry should be deferred to the user/business owner, but login + viewing the resulting screen is often just informational — ask which is actually needed before deciding to stop
2	Treat "login" and "entering payment info" as one bundled decision to skip together	They are different risk levels. Login-then-observe (e.g., see the real cart/checkout price) does not require entering card/account credentials — only the latter needs deferral
3	Report a pre-login/promotional price or state as if it were final, without flagging the gap	If the login-gated final screen wasn't verified, explicitly flag it ("actual payment screen not verified — may differ from the listed price") instead of presenting the pre-login figure as authoritative
4	Assume the backend can't support interactive login without checking	Check chrome-devtools connection + visibility (per credential-issue.md "Fresh-login flow") first; if visible, open the page there and have the user sign in in that same window, then continue capturing
5	Decide unilaterally that "this is good enough" when the report's factual accuracy depends on the gated screen	If the gap could make a delivered report/guide factually wrong (e.g., a payment-request report citing a price that turns out incorrect), the stop-vs-continue decision belongs to the user, not the assistant

Violation case (2026-07-22, 1st)

While building a domain-registration payment-request report, captured the domain-search-result page (showing a promotional price) and the login screen, then stopped at the login wall with a disclaimer ("have finance/ops enter payment details"), never asking whether to continue via login to verify the real checkout price. The report's stated price differed from the actual payment-screen price. User feedback (paraphrased): "don't arbitrarily skip capturing screens that require login — ask first."

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Step 0: Environment Detection (MANDATORY — before any browser action)

Check environment variables AND CLI presence to determine the browser backend:

# wmux
echo "WMUX=$WMUX"
# cmux — detect via ANY of these (cmux app does NOT set CMUX_SESSION; use multi-var OR)
echo "CMUX_BUNDLE_ID=$CMUX_BUNDLE_ID"
echo "CMUX_PANEL_ID=$CMUX_PANEL_ID"
echo "CMUX_BUNDLED_CLI_PATH=$CMUX_BUNDLED_CLI_PATH"
# CLI fallback (env may be unset in nested shells but CLI still works)
command -v cmux && echo "cmux CLI present"
command -v wmux && echo "wmux CLI present"

Do & Don't — Browser Backend Selection

Environment	Detect (ANY true → environment matches)	Do (use this)	Don't (forbidden)
wmux	$WMUX set OR command -v wmux succeeds	wmux browser open/snapshot/click/type commands via Bash	Playwright MCP — user cannot see the invisible Playwright window
cmux	$CMUX_BUNDLE_ID set OR $CMUX_PANEL_ID set OR $CMUX_BUNDLED_CLI_PATH set OR command -v cmux succeeds (e.g. /Applications/cmux.app/Contents/Resources/bin/cmux)	cmux browser panel commands	Playwright MCP — same reason
Plain / tmux	None of wmux/cmux signals present	Playwright MCP (Step 1 below)	—

cmux detection — multi-var OR rationale

cmux app sets several env vars when launching a shell, but CMUX_SESSION is NOT one of them (a legacy guess by analogy with WMUX). Real vars observed in a cmux-launched shell:

• CMUX_BUNDLE_ID (e.g. com.cmuxterm.app)
• CMUX_PANEL_ID (UUID per panel)
• CMUX_BUNDLED_CLI_PATH (CLI absolute path)
• CMUX_SHELL_INTEGRATION_DIR
• CMUX_AGENT_LAUNCH_*
• GHOSTTY_RESOURCES_DIR (cmux uses Ghostty-based terminal)

CMUX_SOCKET is set but often empty — do not use it as the sole signal. Use the OR matrix above.

#	Don't (single-var assumption)	Do (multi-var OR)
1	[ -n "$CMUX_SESSION" ] only check → false negative on cmux app	OR across CMUX_BUNDLE_ID / CMUX_PANEL_ID / CMUX_BUNDLED_CLI_PATH
2	Use CMUX_SOCKET as detection (empty in many cases)	Treat empty CMUX_SOCKET as no-signal; rely on the 3 vars above + CLI presence
3	Assume cmux env var name mirrors wmux (*_SESSION)	Verify against actual cmux app shell environment — vars differ per terminal multiplexer

wmux Browser Commands Reference

When $WMUX is set, use these instead of Playwright MCP.

Invocation form: the rest of this document uses the bare wmux browser … form, which is what runs when wmux is on PATH (the common case). If wmux is not on PATH in the current environment, substitute node "$WMUX_CLI" for wmux in every command below — $WMUX_CLI points to the same entry point. The two forms are interchangeable; pick whichever resolves on the current shell and use it consistently.

wmux browser open <url>          # navigate (= playwright navigate)
wmux browser snapshot            # get accessibility tree with @eN refs
wmux browser click @eN           # click element
wmux browser type @eN <text>     # type into element
wmux browser fill @eN <value>    # set input value
wmux browser get-text            # get page text
wmux browser screenshot          # capture screenshot
wmux browser eval <js>           # run JavaScript
wmux browser back                # go back
wmux browser forward             # go forward
wmux browser reload              # reload page

Workflow: browser open <url> → browser snapshot → read tree → browser click/type @eN → browser snapshot again.

Refs (@e1, @e2...) expire after page changes — always re-snapshot.

Do & Don't — wmux vs Playwright Mapping

Action	wmux (Do)	Playwright MCP (Don't in wmux)
Navigate	Bash("wmux browser open <url>")	mcp__playwright__browser_navigate
Snapshot	Bash("wmux browser snapshot")	mcp__playwright__browser_snapshot
Click	Bash("wmux browser click @eN")	mcp__playwright__browser_click
Type	Bash("wmux browser type @eN text")	mcp__playwright__browser_type
Screenshot	Bash("wmux browser screenshot")	mcp__playwright__browser_take_screenshot
Evaluate JS	Bash("wmux browser eval <js>")	mcp__playwright__browser_evaluate
Wait for text	Re-snapshot + check	mcp__playwright__browser_wait_for

Key difference: wmux browser is visible to the user in real-time on the right panel. Playwright opens an invisible window the user cannot see.

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Quick Reference

After Step 0 backend detection, route to the topic:

Goal	Topic	Entry
Verify a UI change, snapshot, click/fill	ui-test	ui-test.md
Diagnose ::part not applying / closed shadow DOM cascade	cdp-trace	cdp-trace.md
Open a service login → wait for user login → issue access key/token	credential-issue	credential-issue.md

Step execution order: Step 0 (this file — detect backend + user-visibility rule) → read the target topic .md → follow its procedure. The topic .md files hold the actual procedures; this file is the shared backend-detection + index.