LLM Context Window Checker
See how many tokens your text uses across GPT-4o, Claude, Gemini and more
About LLM Context Window Checker
LLM Context Window Checker lets you see how many tokens your text uses across gpt-4o, claude, gemini and more.
Category: AI Tools.
Frequently asked questions
What is a context window?
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The maximum number of tokens a model can process in a single request, including both the prompt (input) and the generated response (output). Exceeding it causes an API error or silent truncation.
How accurate is the token count?
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This tool uses a heuristic (~4 characters per token) rather than each model's actual tokenizer. Counts are approximate — real counts may differ by 10–20% depending on language and content.
What happens if I exceed the context window?
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Behavior depends on the API: some return an error (too_many_tokens), others silently drop the oldest messages. Always leave room for the response — subtract expected output tokens from the limit.
Which model has the largest context window?
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Among mainstream models, Gemini 1.5 Pro supports up to 2,097,152 tokens (~1.5M words). Claude 3.5 Sonnet and Haiku support 200k tokens. GPT-4o supports 128k.