Free developer tool

Context Window Calculator

Estimate whether system prompts, conversation history, retrieved documents, tool schemas, and expected output fit a selected AI model context window.

No account requiredInputs stay in your browser
Token budget

Build your context

Estimated result
978,000
tokens remaining
Fits the selected profile
Total requested72,000 tokens
Context used7%
Context sourceOpenAI
Verified2026-08-22

How to use the result

  1. Choose the exact model profile used by the production request instead of a vendor-wide family name.
  2. Enter separate estimates for system instructions, conversation history, retrieved material, tool schemas, attachments, and expected output.
  3. Use the remaining budget to decide whether to trim history, retrieve fewer passages, summarize context, or reserve less output before sending the request.

How to interpret the answer

The combined total must fit the model context, while requested output may also face a smaller output-token ceiling. A small positive remainder is fragile because tokenizer differences, hidden tool syntax, attachment extraction, or provider-reserved tokens can consume more context than a rough estimate predicts.

A passing result means the entered workload fits the documented constraint represented by this tool. It does not guarantee latency, availability, cost, throughput, or acceptance by every upstream and downstream service.

Assumptions and scope

  • Token counts are estimates unless copied from the provider tokenizer.
  • The tool treats the entered components as one combined context budget.
  • Separate maximum-output limits are checked when the selected profile has one.
  • Provider features may reserve context or apply model-specific behavior not represented here.

Privacy and verification

The calculation runs locally in your browser and does not require an account. Recheck the linked first-party documentation and your live console or response headers before treating the result as a production configuration.

Related

Read the underlying limits