Context Window / Token Budget Planner
🔒 In your browserPlan a prompt's token budget against a model's context window — system, RAG, history, output & cost.
How it works
Add each part of your prompt — system prompt, tool defs, RAG chunks, history — as an estimated token count (or paste text and it's estimated for you), reserve room for the response, and see whether it fits your model's context window, plus the per-call cost. Nothing is uploaded.
Token counts are estimated (~4 characters per token) and windows/prices are bundled reference values — verify with your provider's tokenizer and current pricing before relying on them.
About the Context Window / Token Budget Planner
Every LLM call has a fixed context window, and it's easy to blow past it once you add a system prompt, tool definitions, retrieved (RAG) chunks and conversation history — then reserve room for the response. This free context window and token budget planner lets you lay out each part of your prompt, see whether it fits your chosen model's window, and estimate the per-call cost.
Token counts are estimated locally in your browser; nothing you paste is uploaded.
How to use it
- Pick a model — its context window and pricing are loaded automatically.
- Enter a token count for each segment, or paste text and it's estimated for you (~4 characters per token).
- Reserve tokens for the model's output; the budget bar shows what fits and what's left over.
- Read the per-call input, output and total cost, plus warnings if you're over budget or near the limit.
Why plan a token budget
Overflowing the context window causes truncation or errors, and long prompts cost more and add latency. Planning the budget up front tells you how many RAG chunks you can afford, how much history to keep, and whether a cheaper or larger-context model is the better fit.
Frequently asked questions
How accurate is the token estimate?
It uses the common ~4-characters-per-token heuristic, which is close for English prose but not exact. For precise counts, use your provider's tokenizer (e.g. tiktoken) — the ToolsHub Token Usage Calculator can help.
Are the context windows and prices current?
They're bundled reference values for popular models. Model limits and prices change, so verify against the provider's documentation before relying on them.
What should I reserve for output?
Enough for the longest response you expect. The planner warns if your reservation exceeds the model's typical maximum output.
Does this include prompt caching or batch discounts?
No — it estimates a single standard call. Caching and batch pricing can lower real costs.
Is anything uploaded?
No. All estimates and costs are computed in your browser.
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🔗 Embed this tool on your website — free
Copy this and paste it into your page's HTML. The tool runs in the visitor's browser, just like here. Change height to fit, or add the optional auto-resize snippet below. Add ?theme=dark to the URL for dark mode.
<iframe src="https://toolhq.dev/embed/context-window-planner/" title="Context Window / Token Budget Planner — ToolsHub" width="100%" height="520" style="border:1px solid #e5e7eb;border-radius:12px;max-width:680px" loading="lazy"></iframe>Optional: auto-resize the iframe height
Add this once on the same page so the iframe grows to fit the tool:
<script>
addEventListener("message", function (e) {
if (e.data && e.data.type === "toolshub:resize") {
document.querySelectorAll('iframe[src*="/embed/"]').forEach(function (f) {
if (f.contentWindow === e.source) f.style.height = e.data.height + "px";
});
}
});
</script>