Sandro Fernandes, Developer in Ibiúna - São Paulo, Brazil
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Sandro Fernandes

Verified Expert  in Engineering

Back-end Developer

Ibiúna - São Paulo, Brazil
Toptal Member Since
May 21, 2014

Sandro is driven by a uniquely strong dedication: he has been an entrepreneur from an early age. With extensive experience developing sustainable solutions and a love of learning new technologies, he constantly seeks new challenges and new opportunities to excel.


Karaite Jews of America Inc
Python, Django, Back-end, API Development, Bash, SQL, Supervisord, Gunicorn...
Toptal Clients
HTML, NGINX, Linux, Node.js, Databases, Windows, React, CSS, jQuery, Django...
Isaac Shrem
React, HTML, CSS, CSV, Python, Audio, Videos, PostgreSQL, Django, NGINX...




Preferred Environment

GitHub, MySQL, jQuery, Python, PostgreSQL, React, Django, NGINX, Ubuntu, TypeScript

The most amazing... I've coded are a logo interpreter written in 120 lines of code, a barcode reader on a joystick port, and a full text search for the Hebrew language.

Work Experience

Full-stack Django and Node.js Developer

2021 - PRESENT
Karaite Jews of America Inc
  • Extracted biblical text from Word docs, HTML, and spreadsheets, and compiled a database with those texts.
  • Added audiobooks to books. A record of the text is added to each book, each book has a chapter and verse or paragraph that has a start and end timestamp. We can display the text being chanted in sync with the song.
  • Created back-end APIs and a React front end to display, search, and play out loud biblical texts in Hebrew and English.
  • Developed all infrastructure from scratch using Ubuntu, Django Nginx, PostgreSQL, and Bash.
  • Created an inverted index for the Hebrew language in order to search those texts. The English search was done with a PostgreSQL full-text search.
  • Added text to speech for biblical books in Hebrew and English so that one can listen to the text.
Technologies: Python, Django, Back-end, API Development, Bash, SQL, Supervisord, Gunicorn, APIs, PostgreSQL, React, CSS, HTML, JavaScript 6, Algorithms, Software, API Integration, Software Development, Web, Chrome Developer Tools, Audio, CSV, Material UI, Front-end Development, Data Scraping, Beautiful Soup, Data Modeling, Architecture

Full-stack Developer

2014 - PRESENT
Toptal Clients
  • Developed several applications for international companies, from a simple REST app that took three days to develop to a project spanning eight months.
Technologies: HTML, NGINX, Linux, Node.js, Databases, Windows, React, CSS, jQuery, Django, Python, MacOS, Web Development, Design Patterns, MVC Design, Software, Software Development, Web, Chrome Developer Tools, CSV, Beautiful Soup, Cron, Data Modeling, Architecture

React Developer

2023 - 2024
Isaac Shrem
  • Developed an AI-driven audio/video analysis application, based on which the user may select parts of the video/audio and create new videos/audios in various formats, including VTT, SRT, and GIF.
  • Created a back-end API to be used by the application.
  • Set up account management, creating super users who can admin accounts and videos/audio content via an app. Users had individual accounts, allowing them to upload and download videos.
  • Used a one-time code for authentication that is sent by email and lasts for five minutes. No passwords are stored on the database.
  • Implemented task queue to manage video/audio processing.
Technologies: React, HTML, CSS, CSV, Python, Audio, Videos, PostgreSQL, Django, NGINX, Gunicorn, Ubuntu, Celery, JavaScript, Algorithms, Cron, Data Modeling, Architecture

Back-end Engineer

2023 - 2023
Meadowstone Farm, LLC
  • Enhanced the current application by fixing bugs and adding new features.
  • Updated the current stack to the last versions, Ubuntu, Conda, Django, Nginx, Supervisor, and Gunicorn.
  • Cleaned up code on the back end, removing more than 2000 lines of code.
Technologies: Python, Django, Back-end, API Development, APIs, Bash, JavaScript 6, Software, API Integration, Software Development, Web, Chrome Developer Tools, CSV, Front-end Development, Cron, Data Modeling, Architecture

Lead Software Engineer

2022 - 2022
Dane Roth
  • Developed a new authentication system, using a single expiring key.
  • Solved the CSS site injection that changed the site's look and feel after the extension was activated.
  • Saved lots of money in the long run by changing the back-end infrastructure. There was a better performance by removing calls between data centers and concentrating all on one data center.
Technologies: Django, Python, PostgreSQL, JavaScript, Chrome Extensions, JavaScript 6, CSS, HTML, NGINX, Gunicorn, API Development, APIs, Bash, Software, API Integration, Software Development, Web, Chrome Developer Tools, CSV, Front-end Development, Data Modeling, Architecture

Full-stack Engineer

2019 - 2020
  • Developed the back and front end from scratch using Django, React PostgreSQL, Nginx, and Ubuntu.
  • Worked on the proprietary hardware and software system to do remote inspections. One should buy the hardware (cameras) and a license to use the system. Licenses vary in the number of users and lifespan.
  • Used Twilio, a room to set to gather users and control a remote camera.
Technologies: Django, Twilio API, React, PostgreSQL, APIs, REST, NGINX, Gunicorn, Bash, DigitalOcean, Software, API Integration, Software Development, Web, Twilio, Chrome Developer Tools, Material UI, Front-end Development, Cron, Data Modeling, Architecture

Lead Software Engineer

2017 - 2018
Solvency II Wire Ltd
  • Designed the application that efficiently processes PDFs containing financial data, extracting the relevant information, and seamlessly integrating it into a Postgres database.
  • Created the front-end display of this data as charts, fully searchable and configurable.
  • Contributed to the main objective of presenting a clear and comprehensive overview of insurance companies' performance, including side-by-side analysis.
Technologies: Python, Django, SQL, REST APIs, PostgreSQL, JavaScript, ETL, Excel 2013, Vanilla JS, PDF, Front-end Development, Data Scraping, Data Modeling, Architecture

CEO, Lead Developer, DBA

2007 - 2015
  • Developed a website with two million unique visitors, seven million page views, and a million emails sent per month.
  • Implemented a MySQL database schema with a high availability design in mind.
  • Developed a CMS in Django tailored to Guiadobebe's needs.
  • Installed and configured secure Linux servers back end.
  • Developed applications and improved the site's SEO.
Technologies: Linux, MySQL, Django, Python, Bash, CSS, HTML, NGINX, Cache, Content Management Systems (CMS), Trade, Google Analytics, Full-stack, API Development, SQL, Web Development, Design Patterns, MVC Design, Software, API Integration, Software Development, Web, Chrome Developer Tools, CSV, Front-end Development, Data Modeling


1984 - 2015
Softrent Automação Comercial ltda.
  • Pioneered the use of barcodes in Brazil.
  • Worked as chief developer and organizer.
  • Led the development of solutions for video rental stores, for many years.
  • Gained experience in running a company as a CEO, managing finances and making the main decisions.
  • Trained more than a hundred employees.
  • Performed consulting jobs for many companies.
Technologies: Relational Databases, Django, Python, Web Development, MVC Design, Software, Software Development, Web, Cron

Computer Science Teacher (pro bono)

2005 - 2006
American School in São Paulo
  • Taught teenagers the fundamentals of computer science.
  • Used Lego Mindstorms to help students learn basic computing.
  • Used a 8086 emulator to demonstrate how a microprocessor works.
  • Used Delphi to build small Windows programs illustrating logic, program flow, output, and more.
  • Graded students by skill level.
Technologies: Software

Audio and Video App

I participated in developing an audio and video app that uses AI to analyze the content; based on that, the users can create new videos and audio. My role involved creating both the app's front and back ends while being responsible for server configuration.

Karaites Learning Center
A website that allows people to read and listen to biblical and Karaites-related books. The books are generally in English and Hebrew. I enabled a search feature to search for books in both English and Hebrew, and liturgy songs can be played in-app.

Some challenges were enabling full-text search in Hebrew and synchronizing Hebrew audio books with text.
I was the developer from the start to the end of the project. I was involved in the back and front ends, server config, and installation.

Stack: Django, Python, Nginx, PostgreSQL, React, TypeScript

This was an open source project.

Back End to a POS
Ported a very old back-end for the POS, a Swift application running on an iPad, from Python 2.7 to Python 3.
I collaborated with another engineering team member, and I developed the front-end.
The server resources here are optimized, reducing the monthly bill by 60%.
The dead code was removed.
An improved Django admin was developed so that users add more control.
Updated all stacks for the current version.

Stack used: Django, NGINX, Gunicorn, PostgreSQL, Supervisor

Making Surveys Greener
The company sells licenses to companies that use a remote inspection system. It allows users to avoid travel and its associated expenses, optimizes survey time, and facilitates meetings between experts without the need for travel.

The system is composed of proprietary hardware, mainly video cameras, and software that runs in a browser.

Stack: Django, Django REST Framework, SQLite/PostgreSQL, React, Twilio API, Shopify API

Dane Roth
This is a Chrome extension to search and suggest shows based on the web pages visited.

Stack: Django for the back end, jQuery and vanilla JavaScript for the front end, PostgreSQL as the relational data, Redis as cache, and Heroku as the hosting provider.

Survey System (via Toptal)

Surveys on drivers from Lyft, Uber, and others. The user uploads a picture of the Lyft app screen to the website, on the background Google Vision API is used to read the text in the screen image. Based on that, some checks are made and some statistics are generated.

To incentivize the drivers to post, a fee is paid for each week that the drivers upload images. To upload, the driver must have an account. Payments are made using a PayPal account.

Stack: Flask, React, MongoDB, Heroku, mLab

IDS Consulting (via Toptal)

Acted as a mentor/developer teaching good practices and overall project development.

Stack: Django, REST Framework, Vue, Vuex, SQLite, Heroku

Challenge Your Understanding (via Toptal)

A project dedicated to supporting high-level discussions about any topic.

The user may participate in debates—all are moderated, and each idea can have pro/con responses. It's a meritocracy based on votes.

Stack: Django, Django REST, PostgreSQL, React

Content Management System

Publish/remove content based on time or other criteria.

Supports automatic content cache, without warm-up, optimization of image sizes and minifying of CSS and JavaScript, or page previews.

The content is organized in a tree shape and can be moved around using drag-and-drop. The pages include authentication, and plugins may be inserted in the pages. Any data model may be related with any other model.

The email system is based on templates and integrated with the CMS. The emails sent can collect data such as clicked links and support many other features.

I will be glad to give you a demonstration!

Solvencyii Wire
Web applications to deal with financial data from European insurance companies.

Insurance companies provide balances in PDF format. Those are scanned and translated into Excel spreadsheets. And, after human checking, they are imported into a database. From there, many queries are possible in a web UI.

CHEP Aerospace (via Toptal)

Redis cache for a Python application controlling thousands of ULDs and airplane flights.

Smarking, Inc. (via Toptal)
Django REST API to allow clients to get data.

CFMC | Qualtrics Surveys (via Toptal)
A Django REST framework application to tally surveys in a remote PHP client, using AWS Linux and EC2.

A Portuguese to Portuguese Dictionary in React
Features that are calculated and displayed in this product include given meanings to words, verb conjugation, sound-a-like words, anagrams, syllable division, and plurals. Also, spelling localization is included for Portuguese of Portugal and Brazil.

Stack: Django, Django REST, NGINX, Node.js, React

Ad Server

Tally served banners and ads.

Controlling campaigns, by client, by time, quantity, and user geolocation. Reports are generated by client, ad campaigns, click rate, etc.

Stack: Python, Django, jQuery, MySQL, Ubuntu, Nginx, DigitalOcean

Flight Vector Tracker
Control pilots’ flight time, certifications, training, etc., in a single-page app able to work offline, syncing data when an internet connection is available. Desktop, iPad, and cell phone compatible.

Newsletter Series

The goal of the system is to automatically send a series of newsletters.

The system works based on a timeline around a main event. The timeline may precede and/or succeed the event. Each milestone is associated with an email template and a number of days before or after the main event. On the due date, the email is sent.

The email templates are integrated with user profiles so that message can be personalized.

Stack: Python, Django, jQuery, Cron, Bash, MySQL, Nginx

I ported a Python 2.7 application to Python 3.8. This application collects data from several internet resources using APIs, and all the data is organized in a relational database. The goal was to select candidates for school donations.

Various clients, including universities, paid for this information.
1980 - 1984

Bachelor of Science Degree in Physics

Fundação Educacional de Bauru - São Paulo, Brasil


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API Development, jQuery, React, REST APIs, MobX, Beautiful Soup, Node.js, Pandas, Twilio API


NGINX, PyCharm, Figma, Chrome Developer Tools, Cron, GitHub, Pytest, Jenkins, Microsoft Excel, Git, Google Analytics, Supervisord, ChatGPT, Excel 2013, Celery


Django, Django REST Framework, Material UI, Vanilla JS


Python 3, SQL, HTML5, CSS3, JavaScript, HTML, CSS, Python, TypeScript, Python 2, Bash, JavaScript 6


REST, Object-oriented Programming (OOP), Object-relational Mapping (ORM), Design Patterns, MVC Design, HIPAA Compliance, ETL


Ubuntu, DigitalOcean, Web, Linux, Firebase, MacOS, Windows, Twilio


Databases, MySQL, Database Management, Redis, MongoDB, PostgreSQL, Redis Cache, Relational Databases, Neo4j, SQLite, Cache


Back-end, APIs, Ubuntu Server, Content Management Systems (CMS), Full-stack, Full-stack Development, Front-end, Web Development, Software, API Integration, Software Development, Audio, CSV, Front-end Development, Data Modeling, Architecture, Web Scraping, Startups, Data Scraping, PWA, Progressive Web Applications (PWA), Data Handling, Health Policy, Trade, Physics, Mathematics, Lab, Reports, Gunicorn, Open Source, OpenAI GPT-4 API, OpenAI, OpenAI GPT-3 API, DALL-E, OpenAI API, Generative Pre-trained Transformers (GPT), Chrome Extensions, Algorithms, PDF, Videos, ChatGPT Prompts

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