Agent Skills: Using webctl in Claude.ai Containers

Using webctl in Claude.ai Containers

Browser automation using webctl CLI with automatic proxy authentication handling for Claude.ai's egress-controlled environment.

When This Skill Applies

• User requests browser automation, web scraping, or page interaction
• webctl commands fail with ERR_TUNNEL_CONNECTION_FAILED
• Playwright/Chromium needs to work through authenticated HTTP proxy

Core Problem

Claude.ai containers route traffic through an authenticated egress proxy (HTTP_PROXY env var with JWT credentials). Chromium doesn't properly handle proxy authentication for HTTPS CONNECT tunnels, causing all HTTPS navigation to fail even though curl works.

Solution

A local forwarding proxy (port 18080) intercepts Chromium connections and injects Proxy-Authorization headers before forwarding to the real egress proxy.

Setup Procedure

1. Install webctl

pip install webctl --break-system-packages
webctl setup  # Downloads Chromium if needed

2. Deploy Auth Proxy Module

Copy scripts/auth_proxy.py to webctl's daemon directory:

cp /mnt/skills/user/using-webctl/scripts/auth_proxy.py \
   /usr/local/lib/python3.12/dist-packages/webctl/daemon/

3. Patch Session Manager

Apply this patch to /usr/local/lib/python3.12/dist-packages/webctl/daemon/session_manager.py:

Find the context creation block (around line 104):

# Create context
context = await browser.new_context(
    storage_state=storage_state, viewport={"width": 1280, "height": 720}
)

Replace with:

# Create context with proxy from env (with auth handling)
from .auth_proxy import get_local_proxy_url
proxy_url = get_local_proxy_url()
proxy_config = {"server": proxy_url} if proxy_url else None

context = await browser.new_context(
    storage_state=storage_state, 
    viewport={"width": 1280, "height": 720},
    proxy=proxy_config
)

4. Verify

webctl start --mode unattended
webctl --quiet navigate "https://github.com"
webctl snapshot --interactive-only --limit 10
webctl stop --daemon

Quick Reference

Session Management

webctl start --mode unattended    # Headless browser
webctl stop --daemon              # Full shutdown
webctl status                     # Current state + console error counts

Navigation

webctl navigate "https://..."
webctl back / webctl forward / webctl reload

Observation

webctl snapshot --interactive-only --limit 30   # Buttons, links, inputs
webctl snapshot --within "role=main"            # Scope to container
webctl query "role=button name~=Submit"         # Debug queries
webctl screenshot --path shot.png

Interaction

webctl click 'role=button name~="Submit"'
webctl type 'role=textbox name~="Email"' "user@example.com"
webctl type 'role=textbox name~="Search"' "query" --submit
webctl select 'role=combobox name~="Country"' --label "Germany"

Query Syntax

• role=button — By ARIA role
• name~="partial" — Contains (preferred, more robust)
• name="exact" — Exact match
• nth=0 — Select first when multiple matches

Wait Conditions

webctl wait network-idle
webctl wait 'exists:role=button name~="Continue"'
webctl wait 'url-contains:"/dashboard"'

Troubleshooting

ERR_TUNNEL_CONNECTION_FAILED

Auth proxy not loaded. Verify:

1. auth_proxy.py exists in webctl daemon directory
2. Session manager is patched
3. Restart daemon: webctl stop --daemon && webctl start --mode unattended

Multiple matches error

Add specificity or use nth=0:

webctl click 'role=link name="Sign in" nth=0'

Verify proxy is running

netstat -tlnp | grep 18080

Limitations

• Patch is session-local (container resets clear it)
• Only allowed domains in network config are accessible
• No Firefox support (download blocked by egress policy)

Domain Restrictions

Check <network_configuration> in system prompt for allowed domains. Common allowed: *.github.com, *.bsky.app, allowed API endpoints.

Output Filtering

Reduce context consumption:

webctl snapshot --interactive-only --limit 30    # Cap elements
webctl snapshot | grep -i "submit"               # Unix filtering
webctl --quiet navigate "..."                    # Suppress events