Context Window Simulator - Free Online Tool | PivaBox

Simulate and visualize LLM context window usage — track tokens, conversation turns, and stay within limits

How to Use Context Window Simulator

1. Select an AI model family (GPT-4, Claude, Gemini, or Llama) and choose a context window size preset, or set a custom size
2. Enter your system prompt, conversation turns, and current input text — the tool estimates token counts using the adjustable chars-per-token slider
3. Monitor the visual usage bar and token breakdown to ensure your prompts fit within the model's context window limit

Frequently Asked Questions

Is Context Window Simulator free?

Yes, PivaBox Context Window Simulator is completely free to use. All calculations run locally in your browser.

How accurate is the token estimation?

It uses a character-per-token heuristic (default 4 chars/token for English). For more precise estimates, adjust the slider (3-5 chars/token). CJK characters are not explicitly counted differently — the tool provides a rough estimate for planning purposes. For exact counts, use a model-specific tokenizer.

Why does context window size matter?

Every LLM has a maximum context window — the total tokens it can process at once (system prompt + conversation history + current input). Exceeding this limit causes truncation or errors. Planning your prompt within the context window ensures the model can access all necessary information for a quality response.