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Use Casii MCP in ChatGPT / Codex

The ChatGPT desktop app (ChatGPT Work) and Codex desktop share the same MCP settings and form. Add the Casii MCP server in either app and approve access in your browser on the first connection — no API key needed.

Prerequisites

  1. ChatGPT / Codex installed and signed in.
  2. A Casii account. On the first connection a Casii authorization page opens in your browser — sign in and approve; no API key to create or copy. You can disconnect anytime under Connected apps in the dashboard.

Manage connected apps

Setup steps

  1. Open the ChatGPT desktop app (or Codex) and click the plugins icon in the left sidebar.

    Open the ChatGPT desktop app (or Codex) and click the plugins icon in the left sidebar.

  2. On the Plugins page, click the gear icon to the left of "Add" in the top-right to open plugin settings.

    On the Plugins page, click the gear icon to the left of "Add" in the top-right to open plugin settings.

  3. On the Plugins settings page, click "Add" in the top-right, then choose "Add MCP server".

    On the Plugins settings page, click "Add" in the top-right, then choose "Add MCP server".

  4. On the "Connect to a custom MCP" page, set Name to Casii, Type to "Streamable HTTP" and URL to the MCP URL below. Leave "Bearer token environment variable", "Headers" and "Headers from environment variables" empty, then click "Save" in the bottom-right.

    On the "Connect to a custom MCP" page, set Name to Casii, Type to "Streamable HTTP" and URL to the MCP URL below. Leave "Bearer token environment variable", "Headers" and "Headers from environment variables" empty, then click "Save" in the bottom-right. 
    Name: Casii
Type: Streamable HTTP
URL: https://api.casii.io/mcp/

  5. Back on the Plugins page, "Authenticate" appears next to casii in the server list. Click it — a Casii authorization page opens in your browser; sign in to Casii and approve.

    Back on the Plugins page, "Authenticate" appears next to casii in the server list. Click it — a Casii authorization page opens in your browser; sign in to Casii and approve.

  6. Once authorized, "Authenticate" disappears next to casii and its switch stays on — you are connected. Click "New chat" and ask for what you need in plain language (you can copy the example below).

    Once authorized, "Authenticate" disappears next to casii and its switch stays on — you are connected. Click "New chat" and ask for what you need in plain language (you can copy the example below).

In Codex you can also reach the same page from Settings → Plugins. Do not put an API key in "Headers" — the browser handles authorization.

Verify it works

Ask directly in ChatGPT / Codex, e.g.:

Use casii MCP’s detect_export_target to check how many followers the nasa account has on Instagram

The first call asks for tool permission; after that the AI handles detection, quoting and creation automatically. Creating and resuming must carry a stable idempotency key (idempotency_key, UUID format) generated once: retrying with the same key and the same parameters returns the original tasks and never charges twice; only changed parameters make it a new operation with a new key.