I built Pumbline after losing an afternoon to a function-calling bug that turned out to be one missing "required" field. The model didn't error. It just quietly stopped calling the tool. Pumbline is a small set of free tools for anyone shipping on OpenAI, Anthropic or Gemini: • JSON Schema Validator: paste a tool definition and see exactly what each provider will reject or silently ignore • Prompt Diff Checker: word-level diff between two prompt versions, with the token delta and what it costs per 1,000 calls • Token Counter + API Cost Calculator: exact tiktoken counts and price per call/month across 12 models Everything runs in your browser, and no account is needed to use the tools. Sign in (free) to save schemas and prompts, keep version history and share read-only links. Pro ($9/month, 7-day trial) adds unlimited saves, exports, the provider converter and batch validation. I'd love to hear which provider quirks bite you most. I'll add checks for them.

Pumbline

Catch broken tool schemas before your LLM does

Catch broken tool schemas before your LLM does