What does the reserved output space mean?

A model needs room inside the window to write its reply. The bar reserves each model's maximum output tokens, so full means no space left to answer, not just no space left to read.

Which model has the largest context window?

The context leaderboard ranks every catalog model by window size and stays current with the catalog.

All tools

Free tool

Will it fit the context window?

Paste text or enter a token count and see which models hold it, with room left for the reply.

Last reviewed July 17, 2026

How this is computed

Your text is tokenized in the browser (exact for OpenAI-family, per-family ratio estimate otherwise) and compared against each model's context window from provider data. Fit bars reserve the model's maximum output tokens so a technically-fitting prompt that leaves no room to answer is flagged.