Context Window Fit Checker
Paste your prompt stack and see which LLMs fit — with a bar showing how much of each model’s context window you use.
It checks whether everything you want to send will fit in the AI model.
What this tool does
A context window is the model’s working memory for one request. Your system prompt, conversation, documents, and expected answer all share that space. This tool shows which models have enough room.
- Check a large prompt before it gets truncated
- Plan room for chat history, RAG documents, and model output
- Choose a model with enough context without overpaying for unused space
Token count uses chars÷4 (~±15% vs real tokenizers). Context sizes from a snapshot.
· Paste at least one field to see fit results.
Sorted by fit first, then by lowest context usage. Models that overflow appear at the bottom.
| Model | Context | Used | Bar | Status |
|---|---|---|---|---|
| · |
Your text never leaves the browser — nothing is sent to an API. This is a planning tool, not a tokenizer. Trim RAG context or pick a larger-window model when you overflow.
Context windows are hard limits. If your system prompt plus retrieved docs plus chat history plus room for the reply exceeds the model's window, the provider truncates or errors — often silently at the start of the prompt.
We sum four buckets you control and compare the total against published context sizes for major models. The chars÷4 heuristic matches our token cost calculator; use your vendor's tokenizer when the bill matters.