Free Developer Tools
We're building a set of free, no-signup utilities for FastAPI and AI backend developers. Each one solves a small, specific problem we hit ourselves while building FastAPI AI Kit — a JWT debugger, a PostgreSQL connection string builder, a rate-limit calculator, and an LLM token cost estimator. They'll run entirely in your browser, so nothing you paste ever touches a server.
What's coming
JWT Debugger
Paste any JSON Web Token to instantly decode its header and payload, verify the signature against a secret, and check expiry — all client-side, nothing leaves your browser.
PostgreSQL Connection String Builder
Fill in host, port, credentials, and SSL mode to generate a correctly formatted DATABASE_URL for SQLAlchemy, asyncpg, or psycopg — including managed providers like Railway and RDS.
Rate-Limit Calculator
Work out safe per-minute and per-day request limits for your API tiers based on expected traffic, so your FastAPI rate limiter config matches real usage instead of a guess.
Token & Cost Estimator
Estimate OpenAI or Anthropic token usage and dollar cost for a given prompt and response length, so you can price usage-based billing tiers before you ship.
Why we're building these
Every tool on this page started as a script we wrote for ourselves while building FastAPI AI Kit — debugging a JWT at 1am, working out a rate limit before a launch, or estimating what a RAG pipeline would cost in tokens. Turning them into free, hosted utilities means every FastAPI and AI backend developer gets the same shortcuts, whether or not they use the kit.
No signup, no tracking
These tools will follow the same privacy principles as FastAPI AI Kit itself: no account required, no analytics on what you paste in, and no data sent to a third party. Debugging tokens and connection strings often means pasting something sensitive — these utilities are built to run the calculation in your browser and stop there.