To add your API to Claude as a connector, put a remote MCP server in front of it, then add the server's HTTPS URL in Claude under Customize > Connectors > + Add > Add custom connector. Claude doesn't take a REST API or an OpenAPI file directly; it talks to MCP servers. The same server works in ChatGPT: open Plugins, click + and choose Add custom MCP server. Every Claude plan can add custom connectors, and Free accounts get one. To make it available to everyone, submit it to each directory.
How do I add my API to Claude as a connector?
- Pick the operations people need. A few clear tools beat one tool per endpoint. See turn your API into an MCP server.
- Build or generate the MCP server and host it at a public HTTPS address. Claude's servers call it from Anthropic's published range,
160.79.104.0/21, so it can't sit on a private network (Anthropic). - Add sign-in if tools act on someone's account.
- Add the URL in Claude as a custom connector, connect, and try it in a chat.
Can I add a REST API to Claude without an MCP server?
Not as a connector. Connectors are remote MCP servers, so a REST API needs one in front of it: written by hand with an MCP SDK, generated from an OpenAPI spec, or built and hosted by a service. Developers calling Claude through the Messages API can pass the same MCP server's URL in the mcp_servers parameter instead of running their own MCP client (Claude Docs).
Where do I add a custom connector in Claude?
From Anthropic's custom connector guide, read on 4 November 2026:
- Pro and Max: Customize > Connectors > + Add > Add custom connector. Paste the URL, then connect.
- Team and Enterprise: an Owner or Primary Owner adds it under Organization settings > Connectors > Add > Custom > Web. Members then open Customize > Connectors and click Connect. On Enterprise, custom roles with Manage access to Libraries can add them too.
Which Claude plans allow custom connectors?
Free, Pro, Max, Ultra, Team and Enterprise. Free accounts are limited to one custom connector.
Which sign-in does a custom connector support?
| Option | When to use it |
|---|---|
| No sign-in | Public data only |
| OAuth, with Claude's published identity | Your authorization server supports client ID metadata documents. Anthropic recommends it |
| OAuth, registered automatically | Your server supports dynamic client registration |
| OAuth, with your own client | Your provider needs a client you create first |
| Request headers | A fixed API key or bearer token, shared by everyone using the connector |
Claude starts OAuth only on an HTTP 401, sends PKCE S256 on every request and uses https://claude.ai/api/mcp/auth_callback as its redirect address. Details: MCP server authentication.
How do I add the same API to ChatGPT?
Open chatgpt.com/plugins, click +, choose Add custom MCP server, enter the URL, set up sign-in and click Create as a plugin (OpenAI). Account and workspace policies decide who can add one; on Enterprise, creating plugins with MCP servers is off until an admin turns it on (OpenAI).
ChatGPT's sign-in options differ from Claude's. It supports no sign-in or OAuth 2.1 with PKCE, prefers client ID metadata documents and also takes dynamic registration. It can't send custom API keys (OpenAI).
How do I make it available to every Claude and ChatGPT user?
A custom connector works only for the people who add it. To appear in search and one-click install, submit the same server to each directory:
- Claude: at claude.ai/directory/manage, from a paid plan. See Claude's Connectors Directory.
- ChatGPT: at platform.openai.com/plugins, from a verified organization. See ChatGPT's plugin directory.
How Transica does it
Transica reads your OpenAPI spec, drafts each tool's name, description and inputs, and you approve them. It hosts the MCP server on your domain, signs people in with the login your customers already use, and gives you one URL to add in Claude and ChatGPT. WarrantyWarden's API went from its website to Claude answering with a signed-in user's data in 4 minutes 24 seconds on a recorded run (case study).
Common questions
Can I add an OpenAPI spec to Claude directly?
No. Claude connects to MCP servers. An OpenAPI spec is a starting point for generating one.
Do custom connectors work on Claude's free plan?
Yes, one. Paid plans can add more.
Can a custom connector use an API key?
In Claude, yes: a fixed key goes in the connector's request headers and is shared by everyone using it. ChatGPT can't send custom API keys.
Does my MCP server need to be public?
Yes. Claude and ChatGPT call it from their own servers, so it needs a public HTTPS address.
Is a custom connector listed in Claude's directory?
No. It's available only to the people or organization that add it. Listing needs a separate submission and review.
Sources
All read on 4 November 2026.
