Free tools for API costs, backend performance, and developer workflows.
CalcEngine provides fast, accurate engineering calculators for developers. Estimate API costs, token usage, and backend performance instantly.
Browse All CalculatorsStart with these popular tools used by developers every day.
Estimate OpenAI API costs by model, input tokens, and output tokens.
Calculate total allowed requests over any time window given your rate limit.
Measure the exact byte size of any JSON payload in UTF-8.
See the exact Base64-encoded size and ~33% overhead from original bytes.
No sign-ups, no ads. Just instant results.
Tools designed for real developer workflows.
Every calculator shows its formula and worked examples.
No paywalls. Use as much as you need.
Estimate API costs and token usage across models.
Analyze rate limits, bandwidth, and system performance.
Calculate JSON size, payloads, and storage requirements.
CalcEngine helps developers estimate API costs, token usage, and backend performance. These tools are designed for real-world engineering scenarios, including AI applications, infrastructure planning, and performance tuning.
Instead of using spreadsheets or manual calculations, users can quickly model usage, pricing, and scaling behavior using simple inputs.