Calculator Tools vs ChatGPT custom GPTs

The short answer

Calculator Tools is the host for public static web apps. You get a calculator.tools URL on your account. A ChatGPT custom GPT is an assistant inside ChatGPT with extra instructions and tools. Official Calculator Tools GPTs call this host and return a public URL. A GPT that does not call this API does not publish a calculator.tools page.

Use an official custom GPT when you want to stay in ChatGPT. Use the website or MCP when you are not in ChatGPT, or when you want Image to App.

What they do

The GPT Store lets people share specialized ChatGPT assistants. A GPT can browse, call actions, and follow a system prompt. OpenAI runs that runtime. The conversation lives in ChatGPT.

Some GPTs only chat. Some GPTs call external APIs. Calculator Tools publishes GPTs in the second group. Those GPTs are a channel, not a second host.

What Calculator Tools does

Calculator Tools stores the app files and serves the public page. The same API backs the website, MCP, and the official GPTs. You stay the owner.

Files live in one directory. Typical files are index.html plus CSS, JavaScript, JSON, SVG, or similar static files.

Remix, Image to App, and the dashboard exist on this site even if you never open ChatGPT.

Free accounts can publish 3 apps. Pro ($5.99/month) raises the limit to 25.

Where they differ

Feature	Custom GPT (generic)	Calculator Tools
Runtime	ChatGPT	This site's host
Publishes calculator.tools URL	Only if it calls this API	Always, when create succeeds
Works outside ChatGPT	No	Yes
MCP from Cursor or Claude	No	Yes
Browse public apps here	No	Browse

ChatGPT Canvas is a different ChatGPT surface from GPTs. Use the official Calculator Tools GPT or MCP when the job is to publish here.

When to use each

Use Calculator Tools on the website when you want Image to App, screenshot flows, or a browser create path.
Use a Calculator Tools official GPT when ChatGPT is already open and you want a hosted app. See the ChatGPT page.
Use MCP when the assistant is Cursor or Claude, or when ChatGPT is using MCP instead of the GPT Store listing.
Use a different GPT for tasks that are not hosting (tutoring, writing, data analysis). Then come back here to publish the tool.

Limits

Calculator Tools does not operate the GPT Store. Listings, reviews, and ChatGPT uptime are OpenAI's.

A GPT conversation can fail even when the host is fine. If publish fails, try Create or MCP.

Calculator Tools is not a ChatGPT replacement. Official GPTs can publish a finished page here.

Next step

Open an official custom GPT, connect MCP, or start on Create. The first 3 apps are free.

Sources

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