Local Server and API

The local server is the runtime boundary between Desktop, the H5 browser client, and the Claude CLI. It provides REST APIs, the chat WebSocket, provider protocol translation, and Desktop web assets. The packaged Desktop app manages it automatically. Start it manually only for source development, headless deployment, or a custom client.

Start the server

From the repository root:

bun run src/server/index.ts

It listens on 127.0.0.1:3456 by default. Check readiness with:

curl http://127.0.0.1:3456/health

Response shape:

{
  "status": "ok",
  "timestamp": "2026-01-01T00:00:00.000Z"
}

/health is an always-public startup probe. A successful response does not prove that another endpoint is authenticated.

Startup options

Option	Environment variable	Default	Description
--host <host>	SERVER_HOST	127.0.0.1	Listen address
--port <port>	SERVER_PORT	3456	HTTP and WebSocket port
--cli-path <path>	CLAUDE_CLI_PATH	Automatically resolved	CLI started by the server
--auth-required	SERVER_AUTH_REQUIRED=1	Off	Require explicit authentication for capability endpoints

Command-line host and port values take precedence over environment variables. Keep the loopback address for development. Listening on 0.0.0.0 accepts external connections but does not configure H5 authorization, TLS, or a reverse proxy.

Serve the H5 client

For a source launch, build the Desktop web assets first:

cd desktop
bun run build
cd ..
bun run src/server/index.ts

The server automatically finds desktop/dist in the repository. When starting from another directory, provide the absolute build path:

CLAUDE_H5_DIST_DIR=/absolute/path/to/desktop/dist \
  bun run /absolute/path/to/src/server/index.ts

Variable	Description
CLAUDE_H5_DIST_DIR	H5 build directory; it must contain index.html
CLAUDE_H5_PUBLIC_BASE_URL	Fixed public server URL
CLAUDE_H5_AUTO_PUBLIC_URL=1	Try to derive a LAN URL while H5 access is enabled

Configure the H5 token and exact allowed browser origins in Settings → H5 Access. Treat the token like an API key and regenerate it to revoke existing browser access.

Access control

The server classifies the source of each request before granting access to a capability path:

Request	Default behavior
GET /health	Public startup probe
H5 shell and static assets	Public bootstrap content; they do not contain session data
Direct loopback request	Trusted only when client address, Host, and Origin are local and no proxy-trace header is present
Remote capability request while H5 is disabled	Denied for /api, /proxy, /ws, and file capabilities
Remote capability request while H5 is enabled	Requires a valid H5 token and an allowed browser Origin
--auth-required / SERVER_AUTH_REQUIRED=1	Requires explicit authentication for capability endpoints even when H5 is disabled

A TCP peer address of 127.0.0.1 does not prove that the end user is local. A reverse proxy must preserve the public Host or send at least one of Forwarded, X-Forwarded-*, X-Real-IP, or Via, allowing the server to distinguish proxied traffic from direct loopback traffic.

Passing tokens

• REST, provider proxy, and file endpoints: Authorization: Bearer <token>
• Browser WebSocket: /ws/<session-id>?token=<token>

H5 mode uses the token generated in Settings. Explicit --auth-required mode can also accept a bearer token equal to the server's ANTHROPIC_API_KEY, but exposing a model credential for remote access is discouraged. Prefer H5 with its separate token.

CORS restricts browser access to responses; it is not authentication. It does not make a non-browser client safe.

HTTP API surface

Business REST APIs live under /api/* and cover:

• sessions, conversations, search, and filesystem access;
• settings, permissions, models, effort, and providers;
• agents, tasks, teams, and scheduled tasks;
• skills, plugins, the market, and MCP;
• IM adapters and Computer Use;
• diagnostics, Doctor, activity statistics, memory, and traces;
• H5 access control.

For exact request and response shapes, use the current handlers under src/server/api/. The internal /sdk/<session-id> WebSocket is used by the Claude CLI process started by the server; it is not a third-party client API.

/proxy/* is the provider protocol-translation boundary and depends on runtime authentication and model-routing state. Do not expose it as a general-purpose stateless OpenAI proxy.

Chat WebSocket

Clients connect to:

ws://127.0.0.1:3456/ws/<session-id>

Common client messages include:

• user_message and stop_generation;
• permission_response and computer_use_permission_response;
• set_permission_mode and set_runtime_config;
• sync_state and prewarm_session;
• ping.

The server sends connection and session state, text deltas, thinking, tool calls and results, permission requests, retry or fallback state, errors, task or team updates, and pong. Use src/server/ws/events.ts as the complete field contract.

The Desktop client sends a ping every 30 seconds and reconnects if no pong arrives within 10 seconds. Reconnect delay is capped at 30 seconds; it does not stop permanently after a fixed number of attempts. A custom client should reconnect, resynchronize state, and ignore unknown fields added to future messages.

Reverse-proxy checklist

For remote use:

1. Enable H5 on the server, generate a separate token, and configure exact allowed origins.
2. Use HTTPS so the token is never sent over a public network in cleartext.
3. Proxy static assets, /api/*, /proxy/*, and /ws/*.
4. Enable WebSocket upgrade for /ws/*.
5. Preserve the public Host and standard proxy headers.
6. Do not expose the internal /sdk/* path.

Troubleshooting

Symptom	Check
Port does not bind	Whether SERVER_PORT is occupied and contains a valid number
/health works but an API returns 403	The request is classified as remote while H5 is disabled
API or WebSocket returns 401	H5 token is missing or stale, or the WebSocket lacks a query token
Browser reports CORS	The page's exact Origin is in the H5 allowed-origin list
WebSocket reconnects repeatedly	Proxy upgrade support, token forwarding, and proxy idle timeouts
Page returns 404	desktop/dist was not built or CLAUDE_H5_DIST_DIR is wrong
Remote traffic is treated as local	The proxy removed both the public Host and every proxy-trace header