AI Context Window Calculator
Check whether system prompts, history, tools, user input, and reserved output fit within a model context window.
Editable usage, rate, and operating assumptions
Scenario totals and unit economics
Prevent context overflow
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.
Related API billing guides
Read the concepts behind the calculator and adapt the examples to your own API pricing model.
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