About

I'm Breno Coelho. I've spent 21+ years in software engineering, and since 2005 one thread has kept pulling me back: financial systems. It started with PeopleSoft financial modules (AP/AR/Treasury) during the merger of two steel giants, ran through five years leading cards & payments projects at a Brazilian state bank — coordinating business, compliance, Visa and processors — and since 2022 it's been payments full-time: founding engineer at a US payments startup, then architect of the fiat↔blockchain payment platform at 3thix. Along the way I became obsessed with a single question: how do you know the money is right?

That question has a technical answer, and it isn't "test more". It's invariants: properties of a system that must never be violated, no matter what fails, retries, or races. Double-entry that always balances. Transfers that happen exactly once. Reconciliation that catches drift before an auditor does. I specify these things formally (Quint), enforce them with property-based tests and types, and design the orchestration (Temporal, Postgres, Go) so they hold under concurrency and failure.

Right now, the most interesting version of that question is about autonomy: what must hold before an AI writes your payment code — or an agent moves your money? I use AI aggressively in my own systems, and the guardrails that make that safe — specs, invariants, compilers and tests as gates — are the same ones autonomous payment agents will need. I write about both from practice, not from the sidelines.

I've also worked at the boundary where fiat meets blockchains — in production, not in theory. At 3thix I built the unified payment architecture that ran Stripe, Adyen, NMI and Nuvei alongside EVM chains and Solana: hybrid settlement, on-chain finality against off-chain ledgers, custody and auditability under the emerging regulatory landscape for stablecoins.

And I work across the LATAM–US corridor: Portuguese and English, Brazilian banking and US fintech. Cross-border payments — with their FX, reconciliation and regulatory traps — are home territory.

Work with me

I take a small number of consulting engagements with fintech teams — correctness reviews of ledgers and payment systems, and guidance on adopting AI in financial codebases safely. The best way to start is a short email describing your system and what keeps you up at night: breno.c.coelho@gmail.com.

Elsewhere

My open-source work lives on GitHub — including a ledger built in the open with formally specified invariants. I'm also on LinkedIn, and everything I publish lands here first, with a permanent URL and an RSS feed.