I keep running into the same small problem when working with LLMs: a prompt looks fine in a text editor, but I still need to know whether it is going to fit inside the model context window before I send it.

That is why I added a new tool to Tools Online: AI Token Calculator .

It is a browser-based token and context estimator for common AI models. You can paste a prompt, code snippet, document section, or chat draft, pick the provider/model you care about, and see the token count plus context usage immediately.

What it supports

The first version focuses on the models I most often need to plan for:

OpenAI / GPT models

Claude

Gemini

Qwen

GLM

Kimi

For OpenAI models, the tool uses compatible local BPE tokenizers. For the other providers, it shows the result as a local estimate because their exact billing tokenizers are either proprietary or exposed through authenticated APIs.

That distinction is intentional. I did not want the UI to pretend every number has the same precision.…