# Outside agents Agents that T3 Code did not start can work with an environment through its MCP server. They can read projects and threads, start and message threads, and check which providers and models are available. This covers Claude Code or Codex in your own terminal, ChatGPT, and bots that support MCP. Each agent signs in once, and you choose what it may do. ## Add T3 Code to an assistant app Open the command palette (`Cmd/Ctrl+K`) and choose **Use T3 Code in another app (MCP)**, or use the button in **Settings → Sharing & access**. Pick the app and follow the step for that app. Assistants like Poke and Claude run in the cloud, so the wizard first asks you to sign in to T3 Connect and turn it on for the environment. To reach your other machines through the same connection, turn on **Linked environments** in Labs and [link them](./remote-access.md#link-another-environment). When the app opens the sign-in page, choose what it may do and approve with your T3 Connect account. On an older environment, the wizard asks for the level and gives you a code to paste instead. A code works once, for 5 minutes, and approves only that level. For an app that is not listed, choose **Something else…**, add a remote MCP server with OAuth in that app, and paste the URL. Apps that require their own client ID cannot connect. ## Get the MCP URL In **Settings → Environments**, open a saved environment's menu and choose **Copy MCP URL**. The URL is the environment's address followed by `/mcp`, for example: ```text https:///mcp ``` When T3 Connect serves the environment, the copied URL is its T3 Connect address, which agents can reach from anywhere. Otherwise it uses the route this device is connected over, so an agent on the same device can reach it. - **An agent on your own computers** can use `localhost` on the host, T3 Connect, or any `https` address, such as [Tailscale HTTPS](./remote-access.md#tailscale-https). Signing in sends the agent's credentials to the environment, and agents only do that over `https` or to `localhost`. A plain-`http` LAN or Tailscale address, like `http://100.x.y.z:3773`, lets an agent find the environment but not finish signing in. - **A hosted agent**, such as ChatGPT or a bot running in the cloud, must reach the environment from the internet. Use the T3 Connect address. A Tailscale address only works from your own tailnet. ## Approve a sign-in The first time an agent connects, it opens a sign-in page. When the agent reaches the environment through T3 Connect, the page opens on the T3 Code web app: sign in with the T3 Connect account the environment is linked to and approve there, without a code. Otherwise the page opens on the environment. Either page names the agent and where its access goes: - For an agent on your computer, approval returns to a `localhost` address on the computer that opened the page. - For a hosted agent, approval goes to that service, such as `chatgpt.com`. Anyone who runs that service gets the access. Only approve a sign-in you just started. On the environment's own page, enter a code from **Use T3 Code in another app (MCP)**, **Settings → Sharing & access**, or `t3 auth pairing create` on the host. A browser already signed in to the environment with permission to manage access can approve without a code. On the web app, **Use a sign-in code instead** opens the environment's own page. A code from **Use T3 Code in another app (MCP)** already carries the level you picked there. With another code, choose what the agent may do here: **Auto** is selected by default, or the closest lower mode allowed by your organization’s policy. Approving without a code starts at **Read only**: - **Read only** lets the agent read projects and threads and see the available providers and models. It cannot change anything. - **Supervised** through **Full access** also let it start, message and stop threads in every project. A thread it starts or steers cannot run with more permissions than the mode you chose. ## Claude Code ```sh claude mcp add --transport http t3 https:///mcp claude mcp login t3 ``` `claude mcp login` opens the sign-in page in your browser. On a machine without a browser, add `--no-browser`, open the printed URL elsewhere, and paste the final URL back when asked. `claude mcp list` shows `t3` as connected once you approve. ## Codex ```sh codex mcp add t3 --url https:///mcp codex mcp login t3 ``` `codex mcp login --no-browser` prints the sign-in URL instead of opening it. `codex mcp list` shows `t3` with OAuth once you approve. ## ChatGPT Add the environment as a custom MCP app in ChatGPT's apps settings: 1. Create a new app or plugin with a custom MCP server. 2. Set the server URL to `https:///mcp`, using the T3 Connect address. 3. Choose **OAuth** for authentication. ChatGPT discovers the rest; you do not need a client ID or secret. 4. Create the app, then approve the sign-in page that opens. ## Other agents and bots Any agent that supports remote MCP servers over HTTP with OAuth can connect. Give it the MCP URL and choose OAuth, and the agent finds the sign-in settings itself. Agents without OAuth support cannot connect. ## Scripts on the host On the machine that runs the environment, `t3 thread` uses the same tools without a sign-in: ```sh id=$(t3 thread start . "Find why the tests are slow") t3 thread send "$id" "Now fix it" --wait t3 thread show "$id" t3 thread list ``` `.` means the project that contains the current folder; a project id also works. A new thread uses the project's default model and permission mode, and runs in the project folder unless you pass `--worktree `. `send` never interrupts: a busy thread gets the message as its next turn. Pass `-` as the message to read it from stdin. `--wait` prints the agent's reply. It exits 1 when the run fails or stops, and 2 when the agent waits for an answer you give in the app. Add `--json` for a result that always includes the thread id. ## Remove an agent Approved agents appear under **Settings → Sharing & access** like other clients. Revoke one there to cut off its access immediately. A sign-in lasts 30 days; after that the agent asks you to approve it again.