AI Context Window Calculator
Check whether system prompts, history, tools, user input, and reserved output fit within a model context window.
AI Context Window Calculator
Reserve room for prompts, history, tools, output, and tokenizer uncertainty before sending a request.
Frequently asked questions
Practical answers for applying this calculator to a production API billing or usage plan.
Does the context window include output tokens?
For most model APIs, input and generated output share a total context limit. Reserve output capacity before deciding how much prompt history to send.
Why keep a context safety buffer?
Token estimates can differ from actual tokenizer results, and tools or framework messages can add hidden overhead. A buffer reduces unexpected request failures.
How can I fit a request that is too large?
Trim history, summarize older turns, remove unused tool schemas, retrieve fewer documents, split work into stages, or select a larger-context model.
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