Claude Desktop 3P mode: WebFetch fails because domain safety check is not allowed/proxied

[live-long-and-prosper]

Claude Desktop 3P mode: WebFetch fails because domain safety check is not allowed/proxied

Summary

When using CC Switch as the Claude Desktop / Claude Code gateway, Claude Code's built-in WebFetch consistently fails for normal public domains such as:

• github.com
• react.dev
• en.wikipedia.org
• blog.rust-lang.org
• www.rust-lang.org

The error reported by Claude Code is:

Unable to verify if domain <domain> is safe to fetch. This may be due to network restrictions or enterprise security policies blocking claude.ai.

The model API gateway itself is reachable and works. The failure appears to be specific to Claude Code's WebFetch domain safety verification flow.

Environment

• OS: Windows 10
• Claude Desktop: Microsoft Store build 1.8089.1
• Claude Code bundled by Claude Desktop 3P mode: 2.1.142
• CC Switch: Windows desktop app, cc-switch.exe build timestamp around 2026-05-16
• Gateway base URL used by Claude Desktop 3P config:

http://127.0.0.1:15721/claude-desktop

What works

The CC Switch gateway is reachable locally.

With the configured Authorization: Bearer <inferenceGatewayApiKey> header:

GET  http://127.0.0.1:15721/claude-desktop/v1/models    -> HTTP 200
POST http://127.0.0.1:15721/claude-desktop/v1/messages  -> HTTP 200

So this is not a general gateway connectivity issue.

Also, outside Claude Desktop's 3P sandbox, the required Anthropic domain safety endpoint is reachable:

GET https://api.anthropic.com/api/web/domain_info?domain=github.com
-> {"domain":"github.com","can_fetch":true}

The same is true for react.dev, en.wikipedia.org, blog.rust-lang.org, and www.rust-lang.org.

Diagnosis

Claude Code has a hardcoded WebFetch domain safety check:

https://api.anthropic.com/api/web/domain_info?domain=<domain>

WebFetch only proceeds when this returns can_fetch: true.

In Claude Desktop 3P mode, the local enterprise config generated by CC Switch contains:

{
  "coworkEgressAllowedHosts": ["*"],
  "inferenceProvider": "gateway",
  "inferenceGatewayBaseUrl": "http://127.0.0.1:15721/claude-desktop"
}

However, in Claude Desktop 1.8089.1, coworkEgressAllowedHosts: ["*"] does not behave as "allow all domains".

From the bundled Claude Desktop code, ["*"] is translated into a fixed built-in host list, roughly covering package/tooling hosts such as:

• npm registry hosts
• PyPI hosts
• GitHub / GitHub object storage
• Ubuntu archive/security hosts
• crates.io hosts
• Playwright CDN hosts

It does not mean arbitrary egress is allowed.

Most importantly, it does not appear to allow the WebFetch safety-check path:

api.anthropic.com/api/web/domain_info

As a result, WebFetch fails before fetching the target URL, even for ordinary public documentation sites.

Reproduction

1. Configure Claude Desktop 3P mode through CC Switch.
2. Confirm Claude Desktop uses:

http://127.0.0.1:15721/claude-desktop

3. In Claude Code, ask it to use WebFetch on:

https://github.com/
https://react.dev/
https://en.wikipedia.org/
https://blog.rust-lang.org/

4. Observe the error:

Unable to verify if domain <domain> is safe to fetch.

Expected behavior

CC Switch should support Claude Code's WebFetch safety-check flow in 3P mode.

At minimum, the following endpoint must be reachable from the Claude Code / Claude Desktop 3P environment:

https://api.anthropic.com/api/web/domain_info?domain=<domain>

or CC Switch should provide an equivalent compatible implementation/proxy for that endpoint.

Suggested fixes

One of the following would likely solve the issue:

1. Add explicit support for Claude Code's WebFetch domain safety check:

GET /api/web/domain_info?domain=<domain>

returning an Anthropic-compatible response:

{
  "domain": "example.com",
  "can_fetch": true
}

2. Ensure Claude Desktop 3P egress allows:

api.anthropic.com

especially:

/api/web/domain_info

3. Do not rely on coworkEgressAllowedHosts: ["*"] as an "allow all" setting, because in the current Claude Desktop build it maps to a fixed built-in host list rather than arbitrary egress.

4. Provide a CC Switch UI/config option to append explicit WebFetch target hosts and the required Anthropic safety-check host.

Additional note

Changing coworkEgressAllowedHosts from ["*"] to an explicit host list was tested locally. Claude Desktop did read the updated host count, but this caused the 3P setup health status to become unstable (unreachable), even though the CC Switch model endpoints still returned HTTP 200 with the configured bearer token.

Therefore, a proper CC Switch-side compatibility fix is preferable to manually editing the generated Claude Desktop config.

[DOIT-Ben]

已在本地修复这一项，和 #2980 是同一组 Claude Desktop 3P / WebFetch egress 问题。

修复内容：

• 生成 Claude Desktop 3P profile 时默认写入 "coworkEgressAllowedHosts": ["*"]。
• 在 CC Switch 本地 gateway 增加 Anthropic 兼容的 domain safety check 响应：
  • GET /api/web/domain_info?domain=<domain>
  • GET /claude-desktop/api/web/domain_info?domain=<domain>
• 该端点返回 { "domain": "...", "can_fetch": true }，让 Claude Desktop / Claude Code 的内置 WebFetch 安全校验路径不再因为 3P 本地路由而卡在校验阶段。
• 端点仍复用 Claude Desktop gateway bearer token 校验，不开放成匿名接口。

验证：

• cargo test --manifest-path src-tauri\Cargo.toml claude_desktop --lib -- --nocapture
• cargo test --manifest-path src-tauri\Cargo.toml claude_desktop_domain_info_returns_fetch_allowed_for_authenticated_gateway --lib -- --nocapture
• cargo check --manifest-path src-tauri\Cargo.toml --message-format=short

[live-long-and-prosper]

Thanks. Is this fix already included in a public release, or should I wait for the next CC Switch version?

[farion1231]

感谢反馈！

这个问题与 CC Switch v3.16.0 / v3.16.1 中已经修复的一组问题高度重合，主要修复包括 Codex 配置/接管切换、模型目录刷新、工具/插件恢复、Windows 环境检测、以及部分 provider 格式转换问题。

我们先按已覆盖处理并关闭这个 issue。请升级到 v3.16.1 或更新版本后重新验证。

如果升级后仍然可以稳定复现，请在这里补充新的复现信息，我们会重新打开继续跟进：

• CC Switch 版本
• 操作系统
• 相关应用版本
• 当前 provider / 路由配置
• 复现步骤
• 相关日志或截图

感谢帮忙验证。