Connect Codex to thirds.ai with MCP

To use thirds.ai in Codex, you add one MCP server at https://thirds.ai/mcp, and then you sign in on a thirds.ai page or give Codex an API key through an environment variable. With thirds.ai, you save a design once, such as an invoice, a report, a certificate, or a social post. Then you type in new details and get a finished PDF or image with your logo, colours, and fonts. Once you connect it, you can ask Codex to build those designs and make the files for you. Each successful PDF or image costs one credit.

You stop rebuilding the same file by hand in each chat, and every file keeps the same look. A verified account gets 50 free credits each month, as the credits and billing page says, so you can try it before you pay. You can use Codex in the ChatGPT desktop app, the Codex CLI, and the IDE extension.

You don't need Codex to make a file. To make one in the editor without code, read how to make a template you can reuse. After setup, the Codex file workflows give you designs and prompts to try. To give Codex the steps for a whole file task, such as a report for each client, install a guide from the agent skills library.

Add the thirds.ai MCP server to Codex

You add the thirds.ai MCP server to Codex with one command, and then Codex signs in with only the URL or with an API key. All you need is a thirds.ai account. OpenAI's Codex MCP guide (checked 27 September 2026) says Codex supports OAuth sign-in for remote servers, and thirds.ai uses OAuth when you give only the URL.

Sign in with only the URL

Run these two commands. The second one opens a thirds.ai page. Sign in if you need to and click Allow.

codex mcp add thirds --url https://thirds.ai/mcp
codex mcp login thirds

In the ChatGPT desktop app, open Settings and select MCP servers. Select Add server, enter thirds as the name, choose Streamable HTTP, and enter https://thirds.ai/mcp. Save the server and select Restart. Then select Authenticate for thirds in the server list, and click Allow on the thirds.ai page. In the IDE extension, the same steps start from the gear menu.

This connection gets every thirds.ai tool except the two AI image tools. Sign in with an API key when you need those. To stop the connection, open your thirds.ai Settings, find the app under Connected apps, and click Disconnect. The app loses access right away.

Sign in with an API key

Create an API key on the API keys page. Set it as THIRDS_API_KEY in the environment that starts Codex. Then run this command:

codex mcp add thirds --url https://thirds.ai/mcp \
  --bearer-token-env-var THIRDS_API_KEY

For the same setup by hand, add this table to ~/.codex/config.toml:

[mcp_servers.thirds]
url = "https://thirds.ai/mcp"
bearer_token_env_var = "THIRDS_API_KEY"

For one trusted project, you can put the same table in .codex/config.toml. Codex reads the named environment variable and sends it as a bearer token, so your key never goes in the file. The same Codex MCP guide defines this TOML format, and codex mcp add --help lists the --bearer-token-env-var flag. If you also use Warp, it can load this same server from your Codex config, as the Warp MCP setup guide explains. OpenCode keeps the key out of its file the same way, with {env:THIRDS_API_KEY} in the OpenCode MCP config.

Add the thirds.ai plugin to Codex

The thirds.ai plugin adds the same server to Codex as a package you install, and you sign in with only the URL. The plugin lives in the public thirds.ai skills repository, in the chatgpt-plugin folder. You add it through a personal marketplace file in three steps. OpenAI's plugin packaging guide defines this file and says Codex reads it from ~/.agents/plugins/marketplace.json (checked 30 September 2026).

1. Save this file as ~/.agents/plugins/marketplace.json. If the file already exists, add the thirds.ai entry to its plugins list.

{
  "name": "thirds-ai",
  "interface": { "displayName": "thirds.ai" },
  "plugins": [
    {
      "name": "thirds",
      "source": {
        "source": "git-subdir",
        "url": "https://github.com/thirdsai/skills.git",
        "path": "./chatgpt-plugin",
        "ref": "main"
      },
      "policy": { "installation": "AVAILABLE", "authentication": "ON_INSTALL" },
      "category": "Productivity"
    }
  ]
}

2. Install the plugin. In the Codex CLI, run this command. You can also type /plugins in the Codex CLI and install it from the list.

codex plugin add thirds@thirds-ai

3. Sign in. Run codex mcp login thirds, then click Allow on the thirds.ai page. Start a new Codex session to use the plugin.

In the ChatGPT desktop app, restart the app after step 1 and install the plugin from Plugins, as the ChatGPT setup shows. OpenAI's plugin guide says the IDE extension doesn't support plugins, so use the MCP server there. The plugin adds the server only. To give Codex the steps for whole file tasks too, install the agent skills library.

What Codex can and can't do with thirds.ai

Codex can make PDFs and images from gallery templates and your saved designs, in your own logo, colours, and fonts. Codex works only with the designs, brand kits, and files in your own thirds.ai account, and it spends that account's credits. Ask Codex to show the cost before each paid step.

Codex can find your designs and brand kits, make a PDF, PNG, JPEG, or WebP, preview a design for free, save a brand kit, and turn HTML, a description, or a picture into a design you can edit. It can also make one file for each row of a list, fit an image design to new sizes, and export carousel slides. With an API key, it can make AI pictures too.

Codex can't edit a PDF or Word file you already have. It can't make videos, post to social networks, or send email through thirds.ai. With a URL sign-in or the plugin, it can't make AI pictures.

Check the connection in Codex

You check the Codex MCP connection by listing the servers, then asking Codex for the thirds.ai tools. Restart Codex first if you changed the configuration or the environment. Then run:

codex mcp list

The list must show thirds. Inside the Codex CLI, you can also type /mcp to see the active servers. Then ask Codex to list the thirds.ai tools.

Read the main MCP guide before your first paid call. It explains credit approval and safe retries.

Privacy, terms, and help

When you connect Codex, it can make files and read and change your designs and brand kits with your thirds.ai account and credits. Our privacy policy says what we keep about each connected app and for how long, and the Terms of Service cover your use of thirds.ai through Codex. For help with the server, the plugin, or a failed file, contact support.

FAQ

Why does Codex show that the token is missing?

Check that THIRDS_API_KEY is set in the environment that starts Codex. A terminal variable may not be available to an app that you open from the dock. To test the key itself outside Codex, run the curl check in the MCP Streamable HTTP client guide.

Can I put the API key in http_headers?

Codex supports static headers, but bearer_token_env_var keeps the key out of the configuration file. Use the environment variable for this setup.

Does this setup work in the ChatGPT desktop app?

Yes. Codex is part of the ChatGPT desktop app. OpenAI's Codex MCP guide says that the desktop app, the Codex CLI, and the IDE extension share the MCP configuration (checked 27 September 2026), so you add the server once. Restart the client after you add the server.

Does connecting spend credits?

No. Connecting and listing tools don't spend credits. AI template work and successful renders can. Ask your agent to show the action and the cost before it starts paid work.