What you learn
- Calling Gemini and Claude APIs directly, including the free Gemini tier
- Forcing structured JSON output so a model response becomes a database record
- Two founder case studies: invoice assignment and Swiss trading cards, photo in, record out
Summary
The biggest shift in building software is this: when the tool you need does not exist, you build it the same afternoon. Model APIs let you call an LLM from your own code, with your own prompt, and - crucially - get structured data back instead of a wall of prose. Once a model can reliably turn an image or a document into a clean JSON record, a whole class of manual data-entry work disappears. This lesson teaches the direct API call, the structured-output trick that makes the response usable, and two real tools the founder of this school built from exactly these pieces.
What you will learn
You will learn to call Gemini and Claude directly with a minimal fetch request, to force the model to return JSON matching a schema so the output drops straight into a database, to use vision so a photo becomes structured data, and to recognise when building a small internal tool beats paying for SaaS. The two founder case studies make it concrete: photo of an invoice in, assigned record out; photo of a trading card in, catalogued record out.
Prerequisites
Courses 1 to 3. You need the model-selection lesson from Course 1 (tool cost depends entirely on which model you call), the secrets discipline from Course 3 (the API key never touches client code), and a database to write into - Convex from Course 3 is perfect. The Fundamentals page on what an API is covers the request basics if you need them.
An API is a way for two programs to talk to each other. Learn what an API is, how it works, and why it matters for building with AI.
Tokens are the chunks of text AI models read and are billed in. Learn what a token is, why it matters for cost, and how it differs from a password token.
A .env file stores secrets like API keys outside your code so they never get published. Learn what it is, how it works and how to keep it safe.
JSON, YAML and Markdown are three plain-text formats you will meet constantly. Learn what each is for and how to read them at a glance.
The problem
Businesses pay monthly for SaaS tools that do one narrow thing - read receipts, tag images, extract fields from PDFs - and still do not quite fit their workflow. Meanwhile the same job is a single API call away. The blocker has never been capability; it is that people do not realise how little code stands between "I have a photo of an invoice" and "the invoice is in my accounting system, assigned to the right project". This lesson removes that blocker by showing the whole path end to end.
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