Replit MCP setup to connect Replit Agent to thirds.ai
You connect Replit Agent to thirds.ai by adding a custom MCP server on Replit's Integrations page, with the URL https://thirds.ai/mcp and your API key in one header. With thirds.ai, you save a design once, such as a membership card, an invoice, or a report, with your logo, colours, and fonts. Then you type in new details and get a finished PDF or image. Once Replit Agent has the server, you can ask Agent for those files while you build your app, so you don't write layout code or design each file by hand. Each successful PDF or image costs one credit, and a verified account gets 50 free credits a month.
Give this prompt to your AI agent. The agent does the task for you.
Read https://thirds.ai/docs/mcp/replit and help me connect Replit Agent to thirds.ai with an API key
This page covers Replit Agent connecting out to thirds.ai. It isn't about the Replit MCP Server, which lets other AI apps build Replit Apps. Replit's Connect through MCP page (read on 25 September 2026) explains both directions.
Make it without code
You can make a branded membership card in the thirds.ai editor without Replit or any code. It takes three steps, and you need a free thirds.ai account. Make one card this way first, so you know the design looks right before Replit Agent uses it.
- Open the Membership card template and click Use this template. Sign in and verify your account first if you need to.
- Open the Data tab and type your club name, the member's name, their tier, and the date the pass runs to. Click Preview with data above the canvas to see the card. The preview is free.
- Click Export, then Save and export PNG, and click Download image.
When you want Replit Agent to make the next card for you, add the thirds.ai MCP server to Replit Agent.
How do I add a custom MCP server to Replit Agent?
You add thirds.ai to Replit Agent as a custom MCP server in four steps, and you need a thirds.ai API key first. Replit's Connect via MCP guide (read on 27 September 2026) says you add any server that isn't on Replit's list by its HTTPS address, with custom headers under Advanced settings.
- Create an API key on the API keys page.
- Go to replit.com/integrations, open the MCP Servers pane, and click + Add MCP server.
- Fill in these values. Open Advanced settings to add the header.
| Setting | Value |
|---|---|
| Display name | thirds |
| MCP Server URL | https://thirds.ai/mcp |
| Header name | Authorization |
| Header value | Bearer YOUR_API_KEY |
- Click Test & save.
Replit's MCP list (read on 25 September 2026) says Replit sends custom headers with every MCP request, and that all MCP traffic passes through Replit's security scanner.
Connect with only the URL
You can skip the key and sign in on a thirds.ai page. Add the server with the same display name and URL, leave out the header, and click Test & save. The Connect via MCP guide says Replit walks you through any OAuth flow the server needs (read on 27 September 2026). When the thirds.ai page opens, sign in if you need to and click Allow.
This connection gets every thirds.ai tool except the two AI image tools. Use the header setup when you need those. To stop the connection, open your thirds.ai Settings, find the app under Connected apps, and click Disconnect.
Check that Replit Agent sees the thirds.ai tools
You check the thirds.ai connection by asking Replit Agent to list the thirds.ai tools. Replit's Connect via MCP guide says Agent loads a saved server's tools across all your projects, so you connect once. You should see list_templates, render, and get_status.
Ask Agent to list your saved designs next. Listing is free. If thirds doesn't show up, open replit.com/integrations and check its status under MCP Servers.
Make your first file from Replit Agent
Your first file from Replit Agent starts with a plain request that names the server. Try "Use the thirds MCP server to make a membership card for Priya Patel, Studio member, valid through 31 March 2027, from my Membership card template." Replit's guide says you see a prompt before any tool that needs your confirmation runs.
Ask Agent to show the file count and the credits before paid work. Read the main MCP guide before your first paid call. It explains credit approval, safe retries, and status checks. If your Replit app should make files from its own code instead of through Agent, use the REST API and API workflows.
FAQ
Does Replit support MCP?
Yes. Replit Agent connects to MCP servers, and Replit's MCP list (read on 25 September 2026) shows servers you add in one click and a way to add your own by URL. thirds.ai isn't on that list, so you add it as a custom server.
Why does Test & save fail?
Check that the URL is https://thirds.ai/mcp and that the header is Authorization with Bearer and an active key. Replit's Connect via MCP guide (read on 25 September 2026) asks for the server's HTTPS address, so a server that runs only on your own computer won't connect.
Where do I put the API key?
Put it in the custom header value. Keep the key out of the URL, README files, and install links.
Does connecting spend credits?
No. Connecting and listing tools don't spend credits. AI template work and successful files can. Ask your agent to show the action and the cost before it starts paid work.