01
Understand
Definitions, formulas, assumptions, worked examples, operational limits, and the sources behind them.
An open-core knowledge system for financial software
FinTech is not a feature.
It is an engineering discipline.
Built for the people who turn financial definitions into data contracts, edge-case policy, audited code, and systems that have to be right.
Open core10Published domains
36Algorithm families
203Complete builds
2×Reference languages
Define the contractModel the edge caseImplement twiceTest the meaningShip the evidence
Featured builds
Start where finance
meets implementation.
Each published topic is a complete engineering package—not a glossary entry and not a code snippet without context.
View all finished articles01
The manifesto
Most financial bugs begin before the code.
They begin when a definition is treated as obvious, an input universe is left implicit, or an edge condition is quietly converted into zero.
The Fintech Builder exists for engineers who want the whole chain of reasoning: the source, the interpretation, the contract, the implementation, the tests, and the limits.
We write to make financial behavior reproducible across teams and languages—not merely understandable for the next five minutes.
Our positionCorrect arithmetic is the beginning of financial software quality, not the end.
The topic system
One concept.
Every layer required to trust it.
The knowledge base follows the same path a serious engineering team should follow—from definition to deployable behavior.
02
Contract
Input schemas, invariants, revision identity, edge states, and outputs that keep their meaning.
03
Implement
Dependency-light Python and TypeScript versions designed to agree on the same safe domain.
04
Prove
Fixtures, tests, diagrams, and interactive labs that expose behavior instead of hiding it.
Built for real engineers
Read less folklore.
Ship more certainty.
Browse only topics that are genuinely complete. No empty taxonomy pages, no “coming soon” dead ends, and no article published before its implementation exists.
Open the complete libraryWhy we built this
We kept hitting
the same wall.
“When I first stepped into FinTech, the field was enormous and its algorithms were scattered everywhere — a formula in one paper, a snippet in another repo, half an explanation buried in a forum thread.”
The Fintech Builder is the answer to that fragmentation: one continuous learning journey, one algorithm at a time — explained, visualized, and shipped as real, runnable code you can install and build on. First built to learn. Shared so nobody has to hit that wall again. All of it in the open.
1219Algorithms indexed
224Algorithm families
48Domains mapped