AI API Costs Are Surprising People — Here's How to Check First

A developer built a free browser-based token counter that handles OpenAI, Anthropic, and Google models, providing exact or estimated token counts and custom pricing. The tool aims to help developers avoid surprise API costs by understanding token usage before sending requests. The developer emphasizes that most token counters are inaccurate and that output tokens are often overlooked.

You're building something with the OpenAI or Anthropic API. It's working well. Then you check your usage dashboard and the number is... not what you expected. This happens to almost everyone who builds with AI APIs for the first time. Not because the pricing is hidden - it's published clearly - but because tokens are not an intuitive unit of measurement, and the costs compound in ways that aren't obvious until you're already past them. Tokens aren't words. They aren't characters. They're chunks of text a model's tokenizer splits your input into, and the exact split depends on the model. Rough rules of thumb: The same sentence can be a different number of tokens depending on which model you're using. This is normal and expected. Most people focus on input cost your prompt and forget about output cost the completion . This is a mistake because: Most AI token counters claim to give you an exact count for any model. Most are lying, or at best, guessing. Exact token counts are only possible when you have access to the model's actual tokenizer. Today that means: A tool that claims to give you an exact Claude token count is giving you a confident approximation. That's fine as long as it's honest about it. Most aren't. Three things worth knowing before you send: Show how each of these plays out differently across GPT-4o, Claude Sonnet 4, and Gemini 2.5 Flash using the same prompt. "I built a free token counter that handles all three major providers, is upfront about which counts are exact vs. estimated, and lets you add custom pricing if the built-in table is out of date. No signup, runs entirely in your browser." | Model | Context Window | Input per 1M | Output per 1M | |---|---|---|---| | GPT-4o | 128K tokens | $2.50 | $10.00 | | GPT-4o mini | 128K tokens | $0.15 | $0.60 | | Claude Opus 4 | 200K tokens | $15.00 | $75.00 | | Claude Sonnet 4 | 200K tokens | $3.00 | $15.00 | | Gemini 2.5 Pro | 1M tokens | $1.25 | $10.00 | | Gemini 2.5 Flash | 1M tokens | $0.075 | $0.30 | Prices change. Check the calculator for the most current verified rates. Knowing your token count before you send doesn't just save money on individual calls. It changes how you think about prompt design - you start making deliberate tradeoffs between context richness and cost, which makes you a better AI application builder.