Context window calculator for prompt length

Find out if your text likely fits a target context window before you run a real request. The check is local and gives you a practical estimate for planning your next step.

Text to check context window fit

Estimated tokens0Heuristic (~chars / 4)

Words0

Characters0

GPT-class(128,000 tokens)

The common 128K tier across GPT-class and most open-weight models

Fits in context

0 / 128,000 tokens0% used

Claude-class(200,000 tokens)

The standard Claude tier for Sonnet and Opus models

Fits in context

0 / 200,000 tokens0% used

Gemini-class(1,000,000 tokens)

The long-context tier, led by Gemini Pro releases

Fits in context

0 / 1,000,000 tokens0% used

Estimate disclaimer: Token count is an ESTIMATE (~4 characters per token). Actual usage depends on the specific tokenizer used by each model provider.

This is the free version

Works where you write

PromptDC rewrites selected text in any app, every browser, your IDE and your terminal on Mac and Windows.

One keyboard shortcut

Select text, press Cmd+Shift+E or Ctrl+Shift+E, review the result, then Replace or Copy. It never presses Enter for you.

Your profiles, your models

Pick a default profile per app, or bring your own API key on the Lifetime plan.

Free here: unlimited, this utility runs entirely in your browser. In the app: from $9/mo, or Lifetime from $69 with your own API key.

This helper is built for moments when context pressure appears suddenly. It combines an estimated token count with common context tiers to suggest whether a draft can be sent as-is or should be split. It is especially useful in coding flows where oversized prompts can break chained operations, and because it is browser-only there are no privacy or billing concerns.

Common questions

No. It is a close estimate used for early planning. Actual support still depends on the model tokenizer and implementation details, so treat it as a risk warning instead of a guarantee.

Yes. The context-window estimate is client-only and can be run repeatedly with no quota. It is purpose-built for frequent local checks while building long prompts.

No, it only answers sizing questions. If you need in-place rewriting across Mac, Windows, browser, and terminal workflows, that is available through paid PromptDC subscriptions.

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Context window calculator for prompt length

This is the free version

Works where you write

One keyboard shortcut

Your profiles, your models

Common questions

Will this tell me exact model compatibility?

Can I rely on this calculator for unlimited checks?

Does this replace PromptDC’s paid editing workflows?

More tools

Write better with AI