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Pumbline
Catch broken tool schemas before your LLM does
Validate function-calling schemas and diff prompt versions for developers building on LLM APIs. Free plan available; sign in to save your work.
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.
About Pumbline on Product Hunt
“Catch broken tool schemas before your LLM does”
Pumbline was submitted on Product Hunt and earned 2 upvotes and 1 comments, placing #150 on the daily leaderboard. Validate function-calling schemas and diff prompt versions for developers building on LLM APIs. Free plan available; sign in to save your work.
On the analytics side, Pumbline competes within Software Engineering, Developer Tools and Tech — topics that collectively have 1.2M followers on Product Hunt. The dashboard above tracks how Pumbline performed against the three products that launched closest to it on the same day.
Who hunted Pumbline?
Pumbline was hunted by Seth. A “hunter” on Product Hunt is the community member who submits a product to the platform — uploading the images, the link, and tagging the makers behind it. Hunters typically write the first comment explaining why a product is worth attention, and their followers are notified the moment they post. Around 79% of featured launches on Product Hunt are self-hunted by their makers, but a well-known hunter still acts as a signal of quality to the rest of the community. See the full all-time top hunters leaderboard to discover who is shaping the Product Hunt ecosystem.
For a complete overview of Pumbline including community comment highlights and product details, visit the product overview.
Seth