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cu.yambr.com is the Yambr-managed Computer Use Server. It does two jobs:
  1. Sandbox host — runs the per-chat Docker containers, bridges the CDP browser, streams the terminal.
  2. Public artifact host — the domain where files created by the model (PDFs, HTML, images, …) are served so they can be linked and previewed.
cu.yambr.com is not the MCP endpoint. The public MCP endpoint is https://api.yambr.com/mcp/computer_use. Calls to https://cu.yambr.com/mcp are not publicly reachable.

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How to reach the MCP tools

All Computer Use tool calls go through https://api.yambr.com/mcp/computer_use with Authorization: Bearer <yambr-key>. The LiteLLM layer there authenticates, tracks spend, picks the right sandbox by x-chat-id, and forwards to cu.yambr.com internally. See LiteLLM gateway.

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File URLs: public

Files the model creates inside its sandbox get URLs of the form:
These are publicly reachable (anyone with the link can fetch them) and scoped to a chat ID. Treat them as unlisted but not secret — don’t write sensitive data to a file and share the link without thinking.

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Previews

For file types Open WebUI knows how to render (HTML, PDF, PNG, JPG, SVG, Markdown, …), the chat UI automatically inserts a preview iframe after the link. The underlying URL pattern is:
The filter looks for links of the form {PUBLIC_BASE_URL}/(files|preview)/... in the assistant’s message and swaps them into the artifacts panel. Full mechanics: Open WebUI filter.

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Uploads

Files you upload in chat land at https://cu.yambr.com/uploads/{chat_id}/{path} (also public, also chat-scoped) and are mounted into /home/assistant/uploads/{chat_id}/ inside the sandbox.

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Session lifetime

Files persist as long as the sandbox container does — CONTAINER_MAX_AGE_HOURS (default 24) after the last request to that chat ID. After that, the container and its files are garbage-collected. If you need longer retention, download the artifact or push it to a durable store yourself.

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Live browser and terminal

Both the CDP browser WebSocket and the ttyd terminal WebSocket are reachable through cu.yambr.com only via chat.yambr.com’s Browser and Terminal tabs — the Open WebUI filter negotiates a session-scoped token before opening the socket. There is no public, unauthenticated way to attach.

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TL;DR