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Context Window Checker
Check whether a prompt or document fits a model’s context window, how much room is left for the answer, and how many chunks you need if it does not.
🔒 Processed locally in your browser — we don’t upload your input.
How to use the Context Window
Every language model has a context window: the maximum number of tokens it can consider at once, including your prompt, any attached documents, the conversation history and the reply it writes. Go over the limit and the request either fails or older content is silently dropped. This checker estimates the tokens in your text and compares them with the window size you choose, then shows how much space remains for the model’s answer.
Common window sizes such as 8K, 32K, 128K, 200K and 1M tokens are available as presets, and you can type any custom value because limits change as vendors release new models. You also reserve a number of tokens for the response; the tool warns you when the prompt leaves too little room, which is a frequent cause of cut-off answers.
If the text is too large, the checker tells you roughly how many chunks you would need and links to the Text Chunker, which splits documents into overlapping pieces suitable for retrieval-augmented generation (RAG) or step-by-step summarisation. The estimate uses the same browser-only method as our Token Counter, so your documents stay on your device.
Frequently asked questions
What counts toward the context window?
System prompt, conversation history, documents, your message and the model’s reply all count.
Why reserve tokens for output?
The answer shares the same window. Without space reserved the reply can be truncated.
Are the presets exact for every model?
They are common sizes. Check your model’s documentation and use a custom value if needed.
Is my document uploaded?
No, it is analysed locally.
About this tool
Check whether a prompt or document fits a model’s context window, how much room is left for the answer, and how many chunks you need if it does not. People also look for: context window checker, token limit checker, llm context length, prompt too long.
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