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01 Backend engineer · Full-product developer

ArthurToledo

I build backend systems that have to work when real money and real users are on the line. When a product needs more than an API, I take it the rest of the way — web, mobile, infrastructure, store release.

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Based: Brazil · UTC−3
Availability: Remote worldwide · open to relocation
Core stack: Node.js · TypeScript · NestJS · AWS
Experience: 6 years · intern to technical lead

Arthur Toledo at his desk — 02 — Short version

Six years shipping software, most of it backend. Most of them at a Brazilian product studio, where I went from intern to technical lead — with a short run on internal systems elsewhere in between — then two years on payments and merchant systems for a bank in Paraguay.

Along the way I published apps to both stores, ran the infrastructure under them, and kept building products of my own. The work below is the evidence.

Payment & merchant systems

REST APIs & microservices

Event-driven services and queues

Web apps in React & Next.js

Mobile apps in React Native

AWS infrastructure & CI/CD

Internal enterprise platforms

Idea to store release

03Selected work

Some of this was built for companies and clients, so I name my role instead of claiming the product.

01Freelance · solo build

Livraria Leitura

Internal social network · API, app, realtime chat, admin panel · ongoing

An internal social network for one of Brazil's largest bookstore chains, built and maintained solo across four repositories: a NestJS API, an Expo app for store staff, a standalone realtime chat service, and a React admin panel. Still shipping.

Read the case study →

admin panel

app screen

02Company project

Payments & merchant platform

One of the largest banks in Paraguay, via DBC · microservices, AWS · 2024—2026

Two years inside a bank's payment stack: merchant onboarding, transaction flows, risk checks and provider integrations, as services that fail predictably instead of loudly.

Read the case study →

Transaction path

merchant → api → risk → provider → ledger

node.js · typescript · microservices · postgresql · dynamodb · aws

03Personal project

SourceTruth

NestJS · PostgreSQL + pgvector · retrieval built by hand

Document Q&A where every answer cites the passage it came from. No framework doing the retrieval for me — chunking, embeddings and ranking are mine, which is the only way to know why an answer is wrong.

Read the case study →

answer view with citations

Also built & shipped

Personal · SaaS

radarleilao

Vehicle auction alerts by subscription: a scheduled scraping worker, a messaging API with queueing and retries, WhatsApp and email delivery, paid tiers.
Personal · product

flyconnecta

An eSIM store for travellers coming to Brazil. Catalogue, Stripe checkout, instant delivery by QR code, five languages, no manual step.
Open source

convert-multiple-files

A document conversion library written to solve a problem at work, then open-sourced. 25 versions, ~10.5k npm downloads a year.
Personal

cripto-trader

A Binance bot that keeps a human in the loop: every proposed trade lands in Telegram with its analysis and waits for a tap.
Personal

quem-e-voce

Realtime multiplayer deduction game. Anonymous play runs with no database and no session — a lint rule keeps it that way.
Personal

love-in-pages

A shared online photo book for couples, with a page-turn reading experience. S3 storage, Stripe and Mercado Pago, delivery by QR code.
Freelance

Marido BH

A service marketplace app taken end to end: client discovery, API, app, deploy.
Freelance

DJ music platform

A platform for a DJ project, built end to end — NestJS API, React front end, AWS.
Personal

Petecou

A match organiser for my father’s peteca group: timers, scores, history, and the sound effects they actually asked for.
Open source

automatic-reddit-stories

A pipeline that turns a Reddit thread into a finished video: scrape, narrate, sync, render. No manual editing.

Interlude · 01

Everything fails eventually. The job is deciding how.

04What I work with

Backend

Node.js
TypeScript
NestJS
Express
Fastify
REST APIs
Microservices

Data

PostgreSQL
MongoDB
MSSQL
DynamoDB
Redis
pgvector

Messaging

RabbitMQ
AWS SQS / SNS
Socket.IO

Cloud & infra

AWS
Docker
CI/CD
GitHub Actions
Nginx
Linux

Frontend & mobile

React
Next.js
Angular
React Native
Expo

Testing

Jest
Vitest
Supertest
TDD

Practices

Clean Architecture
Hexagonal
MVC
Code review

How I work

01
Boring architecture first. Complexity should have to argue for itself, and most of the time it loses.
02
Failure is a design decision. Retries, idempotency and timeouts belong in the first version, not the postmortem.
03
If I can't see it, I don't trust it. Logs, metrics and traces are part of the feature.
04
Shipped beats elegant. I'd rather maintain something real in production than defend a perfect diagram.

Process

Three passes, every time.

01
Understand the system

Before a line of code: what breaks today, who pays when it does, and what the data actually looks like. Most of the work lives here, and it is the part nobody can skip on my behalf.
02
Agree on the contract

Endpoints, schemas, failure modes and limits, settled before implementation. The interface is the design — everything behind it stays free to change later.
03
Ship it and stay on it

Deploy small, instrument everything, and keep watching after release. A system nobody is measuring is a system nobody is running.

The same three passes whether it is a payment service for a bank or a side project nobody asked for.

Interlude · 02

Six years, five titles, one direction: more of the system, end to end.

05The route so far

2026 —

Remote

Freelance developer

Independent

Backend and full-product work for clients, plus my own products. I scope, build, deploy and keep it running.

2024 — 2026

Remote · client in Paraguay

Senior Backend Developer

DBC Company

Payment and merchant microservices for one of the largest banks in Paraguay. Provider integrations, transaction and risk flows, event-driven services, PostgreSQL and DynamoDB on AWS.

node.js · typescript · microservices · postgresql · dynamodb · aws

2021 — 2024

Remote

Mid-level → Technical Lead

Squadra Digital

Aug 2023 · Technical Lead
Nov 2022 · Senior Developer
Dec 2021 · Mid-level Developer

Second run at the same company: three titles in under three years, ending with architecture decisions and delivery leadership on enterprise systems.

nestjs · typescript · angular · clean architecture · mssql · redis · rabbitmq · jest · jenkins

Second tenure — I left for Grupo Zelo and came back.

2021

Hybrid · Belo Horizonte

Mid-level Developer

Grupo Zelo

Three months on internal systems for a large services group, on-site with the teams that used them. Hexagonal architecture, AWS messaging, tests written first.

node.js · nestjs · mongodb · aws sns/sqs/ecs · jest

2020 — 2021

Remote

Intern → Developer

Squadra Digital

Where it started. Nine months as an intern, then eight as a developer, learning to ship on systems other people depended on.

Interlude · 03

Remote since 2020 — which is how the map got involved.

06Off the clock

I've worked remotely for most of my career, which turned out to be the best excuse to see places. Glaciers in Patagonia, trails on a mountain bike, a surfboard I'm still bad at.

Different countries mean different languages and different ways of working. Portuguese is my first, Spanish came from working with people who speak it, English from using it every day — and in 2026 I spent a few months in Ireland on a language exchange. Between contracts I build small products of my own, usually because something annoyed me enough to fix it.

Code is the work. Getting outside is how I reset.

Systems Analysis & Development, UNIASSELVI · Computer Networks, Senac Minas