[Bug] Playwright Browser Download Blocked in Web Environment

Resolved 💬 5 comments Opened Dec 28, 2025 by orangewise Closed Feb 14, 2026

Playwright Browser Download Blocked in Claude Code on the Web

Issue Summary

Playwright browser binaries cannot be downloaded in Claude Code on the web sessions due to missing domains in the egress proxy allowlist.

Status: Blocked
Date Reported: 2025-12-28
Affects: Claude Code on the web sessions
Does NOT affect: Regular Claude.ai chat sessions (confirmed to have access)

The Problem

When attempting to install Playwright browsers in Claude Code on the web:

.venv/bin/python -m playwright install chromium

Error received:

Error: Download failed: server returned code 403 body 'Host not allowed'
URL: https://cdn.playwright.dev/dbazure/download/playwright/builds/chromium/1200/chromium-linux.zip
URL: https://playwright.download.prss.microsoft.com/dbazure/download/playwright/builds/chromium/1200/chromium-linux.zip

Root Cause

Claude Code on the web uses an Envoy proxy with JWT-based allowlist for egress traffic. The proxy configuration is controlled by:

Service: anthropic-egress-control
Proxy server: 21.0.0.89:15004 (container-specific)
Authentication: JWT token embedded in environment variables
Blocking mechanism: x-deny-reason: host_not_allowed

Why WebFetch Permissions Don't Solve This

Critical architectural limitation discovered: WebFetch permissions in settings.json and ALLOWED_FETCH_DOMAINS hooks only control Claude's WebFetch tool, not subprocess HTTP requests.

Claude Code Container Architecture:
├── Claude's Tools (WebFetch, WebSearch)
│   └── Controlled by: settings.json permissions + hooks ✅
├── Subprocess Tools (Node.js, Python child processes)
│   ├── Playwright's Node.js installer
│   ├── npm install, pip install
│   └── Controlled by: Container-level JWT proxy ❌ (BLOCKED)
└── JWT-based egress proxy
    └── Controls: ALL outbound HTTP/HTTPS traffic

What we tried:

✅ Added Playwright domains to .claude/settings.json WebFetch permissions
✅ Investigated ALLOWED_FETCH_DOMAINS hook approach
❌ Result: Playwright still blocked because it makes direct HTTP requests via Node.js subprocess

Node.js specific limitation: Node.js built-in https module ignores HTTP_PROXY/HTTPS_PROXY environment variables - a documented historical limitation.

Conclusion: This requires infrastructure-level changes to the JWT proxy's allowed_hosts field. WebFetch permissions and hooks cannot override container-level network restrictions.

Current Allowlist Status

The JWT's allowed_hosts field includes hundreds of development-related domains:

✅ storage.googleapis.com
✅ github.com, raw.githubusercontent.com
✅ npmjs.com, registry.npmjs.org
✅ pypi.org, pypi.python.org
✅ microsoft.com, packages.microsoft.com
✅ Many others (npm, maven, docker, gradle, rust, ruby, etc.)

But missing:

❌ cdn.playwright.dev
❌ playwright.download.prss.microsoft.com
❌ *.playwright.dev (wildcard)

Key Discovery: Different Proxies for Different Services

Regular Claude sessions (claude.ai):

Confirmed to have Playwright domains in allowlist
Different proxy infrastructure

Claude Code on the web:

Separate proxy configuration
More restrictive allowlist (security for code execution)
Playwright domains NOT YET added to this specific allowlist

Evidence

1. Fresh JWT Token Analysis

After forcing environment refresh (exec bash):

New JWT issued: iat: 1766917369
Container changed: sad-drab-flaky-comb
Proxy changed: 21.0.0.89:15004
Playwright domains still missing from allowed_hosts

2. Direct Network Tests

curl -I https://cdn.playwright.dev
# Result: HTTP/1.1 403 Forbidden
# Header: x-deny-reason: host_not_allowed

3. Playwright Installation Attempts

Multiple attempts across different containers and JWT tokens - all failed with identical 403 errors.

Requested Domains to Add

Please add the following domains to the Claude Code on the web egress proxy allowlist:

cdn.playwright.dev - Primary CDN for Playwright browsers
playwright.download.prss.microsoft.com - Microsoft CDN mirror
*.playwright.dev (optional wildcard) - Future-proofing for any new subdomains

Impact

Users affected:

Anyone trying to use Playwright for browser automation in Claude Code on the web
Screenshot generation workflows
E2E testing scenarios
Web scraping projects

Current workarounds:

✅ GitHub Actions workflow (has full network access)
❌ Local browser installation (no Chrome/Chromium in container)
❌ Alternative CDNs (none available for Playwright)

Reproduction Steps

Start Claude Code on the web session
Install Playwright: uv pip install playwright --python .venv/bin/python
Attempt browser download: .venv/bin/python -m playwright install chromium
Observe 403 errors from both CDN URLs

Environment Details

Platform: Claude Code on the web
Container OS: Linux 4.4.0
Python: 3.11
Playwright version: 1.57.0
Chromium build: 1200 (143.0.7499.4)

Technical Details

JWT Token Structure

{
  "iss": "anthropic-egress-control",
  "organization_uuid": "[redacted]",
  "iat": 1766917369,
  "exp": 1766931769,
  "allowed_hosts": "[comma-separated list - missing playwright domains]",
  "is_hipaa_regulated": "false",
  "use_egress_gateway": "false",
  "session_id": "[session_id]",
  "container_id": "[container_id]"
}

Environment Variables Affected

HTTPS_PROXY
HTTP_PROXY
GLOBAL_AGENT_HTTP_PROXY
YARN_HTTPS_PROXY
YARN_HTTP_PROXY

All contain the JWT-authenticated proxy URL with the restricted allowlist.

Infrastructure Change Request

Required Action

Add the following domains to the JWT-based egress proxy allowlist for Claude Code on the web containers.

This is an infrastructure-level configuration change to the allowed_hosts field in JWT tokens issued by anthropic-egress-control.

Domains to Add

| Domain | Purpose | Similar Existing Domains |
|--------|---------|-------------------------|
| cdn.playwright.dev | Primary CDN for Playwright browser binaries | Similar to: cdn.cocoapods.org, static.crates.io |
| playwright.download.prss.microsoft.com | Microsoft CDN mirror for Playwright | Similar to: packages.microsoft.com, dotnet.microsoft.com |
| playwright.dev | Playwright documentation and resources | Similar to: docs.claude.com, nodejs.org |

Justification

Playwright is a standard development tool comparable to other package managers and build tools already in the allowlist:

| Tool Category | Already Allowed | Requesting |
|---------------|----------------|------------|
| Package CDNs | npmjs.com, pypi.org, rubygems.org | cdn.playwright.dev |
| Microsoft CDNs | packages.microsoft.com, mcr.microsoft.com | playwright.download.prss.microsoft.com |
| Browser automation | (none) | playwright.dev |

Use cases:

End-to-end testing (E2E tests)
Screenshot generation for documentation
Web scraping and automation
UI testing workflows

Security: Playwright is developed by Microsoft, same trust level as other Microsoft domains already in allowlist.

Technical Implementation

The JWT signing service (anthropic-egress-control) needs to update the allowed_hosts field in the token payload template for Claude Code on the web sessions.

Example JWT field update:

{
  "allowed_hosts": "existing,domains,here,cdn.playwright.dev,playwright.download.prss.microsoft.com,playwright.dev"
}

Testing Verification

After deployment, verify with:

# In Claude Code on the web session:
curl -I https://cdn.playwright.dev
# Expected: HTTP/1.1 200 OK (not 403 Forbidden)

.venv/bin/python -m playwright install chromium
# Expected: Successful browser download

Recommendation

This change enables browser automation workflows in Claude Code on the web, bringing parity with regular Claude.ai sessions which already have access to these domains.

Related Files in This Repository

/home/user/markdeck/CLAUDE.md - Documents the network restrictions
/home/user/markdeck/.github/workflows/screenshots.yml - Working GitHub Actions workaround
/home/user/markdeck/capture_screenshots.py - Playwright screenshot script

Contact

Repository: orangewise/markdeck
Branch: claude/fix-screenshot-generation-N9Uhn
Session: Claude Code on the web

---

References and Sources

Key Findings Summary

WebFetch permissions scope: Only controls Claude's WebFetch tool, not subprocess HTTP requests
Node.js proxy limitation: Node.js ignores HTTP_PROXY/HTTPS_PROXY environment variables
Architecture gap: No user-level mechanism to override container-level proxy restrictions
Recommended solution: Infrastructure-level JWT allowlist update

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Note: This issue is specific to Claude Code on the web infrastructure and does not affect regular Claude.ai chat sessions, which reportedly have access to these domains.

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