API reference

The Computer Use Server speaks standard MCP (Model Context Protocol) over Streamable HTTP. Any MCP-compatible client can connect. Registered in the MCP Registry as io.github.yambr/open-computer-use.

Endpoint

Managed Yambr: https://api.yambr.com/mcp/computer_use — auth with your Yambr API key as Authorization: Bearer sk-yambr-.... Get keys at app.yambr.com. Yambr exposes MCP only; your LLM traffic goes to your own provider — see Access model. Self-hosted: http://localhost:8081/mcp

Authentication

Set the MCP_API_KEY environment variable on the server and pass as a Bearer token:

Authorization: Bearer <MCP_API_KEY>

Leave MCP_API_KEY empty for local dev (no auth).

Required headers

X-Chat-Id is mandatory. Without it (and with SINGLE_USER_MODE=false), the server returns an error. Every request must include a unique session identifier.

Header	Purpose	Required
`X-Chat-Id`	Session identifier — one sandbox container per id	Yes
`Authorization`	`Bearer <MCP_API_KEY>`	If `MCP_API_KEY` is set
`X-User-Email`	User email (per-user skills, PAT lookup, logging)	No
`X-User-Name`	Display name (URL-encoded)	No
`X-MCP-Servers`	Comma-separated MCP server names for the Claude Code sub-agent	No
`Mcp-Session-Id`	Session id from `initialize` response; include on subsequent calls	After initialize

Session isolation modes

Controlled by SINGLE_USER_MODE:

Mode	`X-Chat-Id`	Behavior
unset	Yes	Isolated container per chat id
unset	No	Shared `default` container + warning appended to every tool response
`true`	any	Always one `default` container; header ignored
`false`	Yes	Strict: isolated container per chat id
`false`	No	Rejected with error

See MCP methods for request examples.

Available tools

Tool	Description
`bash_tool`	Execute bash commands in the sandbox with streaming output
`view`	View files and directories with line numbers
`create_file`	Create files (auto-creates parent directories)
`str_replace`	Edit files via find-and-replace with uniqueness validation
`sub_agent`	Delegate to an autonomous Claude Code agent

Full signatures: tools/list · tools/call.

Native MCP primitives beyond tools

Three more native primitives, all scoped by X-Chat-Id:

Primitive	What you get	How
`InitializeResult.instructions`	The per-chat system prompt as a string, delivered in the handshake	Dynamic — re-rendered each stateless request from `X-Chat-Id` / `X-User-Email` headers
`resources/list` + `resources/read`	Uploaded files as `file://uploads/{chat_id}/{encoded-rel-path}`	Auto-registered on container create + on every `POST /api/uploads`

In addition, /home/assistant/README.md inside the sandbox carries the same prompt text — any model that runs view can recover its environment even if the client stripped every MCP handshake field. Full map: system prompt reference.

The server intentionally does not expose the system prompt via prompts/get. MCP prompts/* is user-controlled (slash commands) and PromptMessage.role is restricted to user | assistant — duplicating InitializeResult.instructions there would be off-spec.

Dynamic configuration endpoints

Non-MCP HTTP endpoints that MCP clients should use instead of hardcoding:

Endpoint	Returns
`GET /system-prompt?chat_id=...&user_email=...`	Full per-session system prompt (plain text)
`GET /skill-list?user_email=...`	Skills list for sub-agent prompts
`GET /mcp-info`	Available tools, required headers, endpoint URL (JSON)

Browser endpoint (CDP)

GET /browser/{chat_id}/status
GET /browser/{chat_id}/json
WS  /browser/{chat_id}/devtools/page/{page_id}

See Live browser.

Terminal endpoint

GET  /terminal/{chat_id}/status
POST /terminal/{chat_id}/start-ttyd
WS   /terminal/{chat_id}/ws

See Terminal tab.

File endpoint

GET /files/{chat_id}/{path}
GET /preview/{chat_id}/{path}
GET /files/{chat_id}/archive        # zip of everything in this chat

See File preview and cu.yambr.com.

Per-method details

initialize

Open a session and get Mcp-Session-Id.

tools/list

Enumerate available tools.

tools/call

Invoke a tool.

resources/list

Browse uploaded files.

​Endpoint

​Authentication

​Required headers

​Session isolation modes

​Available tools

​Native MCP primitives beyond tools

​Dynamic configuration endpoints

​Browser endpoint (CDP)

​Terminal endpoint

​File endpoint

​Per-method details

initialize

tools/list

tools/call

resources/list

Endpoint

Authentication

Required headers

Session isolation modes

Available tools

Native MCP primitives beyond tools

Dynamic configuration endpoints

Browser endpoint (CDP)

Terminal endpoint

File endpoint

Per-method details