Context fit
A context window is the whole of what a model can hold at once — your document, the conversation and its own reply. Drop a file or paste text to see how much of each model's window it would take.
Your file never leaves this page. There is no server runtime behind this site: the PDF is parsed and the tokens are counted by your own browser. Nothing is uploaded, nothing is logged, nothing is stored — you can read the network panel and check.
drop a file here — .txt, .md or a PDF
Result
Nothing measured yet. The encoding dictionary is only downloaded once there is text to count, and the PDF engine only when you hand us a PDF.
How the check works
A context window is counted in tokens, and every model has its own size — from 128,000 to about a million. This tool counts your text the way each model would: with the real published dictionary where one exists, and with a clearly marked vendor-derived estimate where it does not. It then shows the share of each window your text would occupy. The share is deliberately conservative in two ways: estimates are chosen to over-count, and the window also has to hold the conversation and the reply — which is why the page warns that a document at 90% of the window is not usable the way one at 20% is.
Common questions
- 1 Does my file leave my browser?
- No. The PDF is parsed and the tokens are counted by your own browser; the site is static files with no server runtime, so there is nowhere to upload to. You can watch the network panel while you use it.
- 2 Which files can I drop?
- .txt, .md and PDF files with a text layer. A scanned PDF without a text layer yields no text — the tool detects that and says so instead of reporting “0 tokens, fits everywhere”, which would be the wrong answer.
- 3 Why are some rows marked as estimates?
- Anthropic, Google and OpenAI (for its newest models) have not published their tokenizers. Those rows divide the character count by the vendor’s own characters-per-token figure, chosen to over-count rather than under-count — so a document the tool says fits, fits.
- 4 If a document fits, can I actually use the whole window?
- Not quite. The window also has to hold the system prompt, the conversation so far and the model’s own reply. A document at 90% of the window is not usable the way one at 20% is — the share column is a budget, not an invitation to fill it.
Want to see the individual tokens rather than the totals? Token counter shows the split.