Available to hire
Hi, I’m Humberto Castro, a senior iOS engineer with 10+ years of experience building scalable, high-performance mobile apps across fintech, edtech, and social platforms. I specialize in Swift, Clean Architecture, and MVVM, with a passion for modularization, offline-first design, and performance optimization. I’ve led architecture and development for apps used by millions, including PayPal, Reddit, and Neon.
I enjoy mentoring teams, collaborating with Product and Design, and delivering reliable solutions in agile, remote environments. Proficient in Swift, Objective-C, RxSwift, Combine, GraphQL, and CI/CD tooling (Fastlane, Bitrise, Buildkite), I combine a strong foundation in data structures and software architecture with hands-on product sense to ship value quickly and safely.
Experience Level
Language
English
Fluent
Portuguese
Fluent
Spanish; Castilian
Intermediate
Work Experience
iOS Developer at Reddit
June 1, 2025 - PresentRemote role focusing on internationalization and translation experiences; ML-driven translation features, A/B experimentation, and analytics to measure engagement across languages.
iOS Developer at Mobi
November 1, 2024 - October 10, 2025Led feature development and architectural improvements on the iOS app; implemented 10+ features; refactored legacy Objective-C modules to Swift; collaborated across Product, Design, and QA.
Senior iOS Developer at Cogna Educação
December 1, 2022 - October 10, 2025Designed and implemented features for the Ampli/.edu app using MVVM and MVP; leveraged RxSwift and Apollo GraphQL; streamlined CI/CD workflows with Fastlane and Bitrise; contributed to modularization.
iOS Developer at PayPal
September 1, 2022 - October 10, 2025Designed, built, and maintained critical components of PayPal’s iOS app used by 50M+ users; implemented MVVM and SOLID principles; achieved 90%+ unit test coverage and a high crash-free rate.
Senior iOS Developer at Cogna Educação
November 1, 2021 - October 10, 2025Led end-to-end architecture and development of Cogna’s flagship education app; created a modular offline-first platform; mentored a small iOS team; integrated CI/CD improvements.
Senior iOS Developer at Neon
March 1, 2020 - October 10, 2025Contributed to Neon’s Loans squad; improved performance and reliability of credit flows; refactored codebase for better modularization; mentored junior developers.
iOS Developer at Mira Educação
April 1, 2019 - October 10, 2025Architected and developed the Mira app from scratch with offline-first design using Realm and GraphQL; implemented MVVM and Clean Architecture; led technical interviews and onboarding.
iOS Developer at Indice.in
December 1, 2016 - October 10, 2025Developed MobEPI, a safety and compliance app; implemented MVVM; integrated Parse and Firebase for real-time data sync; focused on clean UI and usability.
iOS Developer at Apple Developer Academy | Senac
January 1, 2016 - October 10, 2025Developed multiple iOS prototypes; built an offline-first system; integrated third-party SDKs; collaborated in agile teams to deliver prototypes and UX-focused features.
iOS Developer at Reddit
June 1, 2025 - PresentRemote role in Reddit's Internationalization squad focusing on ML-driven translation experiences to enhance accessibility and engagement. Led A/B experimentation for translation features, collaborated with ML, Product, and Backend teams to align execution with localization goals, and implemented analytics to measure engagement and performance of translation experiments.
iOS Developer at Mobi
November 1, 2024 - October 10, 2025Led feature development and architectural improvements on Mobi’s iOS app, used by thousands of subscribers. Implemented 10+ new features with Swift, UIKit and SwiftUI; refactored legacy Objective-C modules to Swift, reducing crash rates and improving maintainability. Collaborated with Product, Design, and QA in agile sprints and contributed to backlog grooming and tech planning.
Senior iOS Developer at Cogna Educação
December 1, 2022 - October 10, 2025Designed and implemented features for the Ampli/.edu app with a modular offline-first approach. Leveraged RxSwift and Apollo GraphQL to improve data reactivity and API communication; reduced UI lag by approximately 20%. Coordinated with cross-functional teams to ship features aligned with OKRs and participated in CI/CD optimization.
iOS Developer at PayPal
September 1, 2022 - October 10, 2025Built and maintained critical components of PayPal’s iOS app used by 50M+ users. Implemented MVVM and SOLID principles to modularize key flows, increased onboarding speed, and wrote unit tests with 90%+ coverage for sensitive modules, contributing to a 99% crash-free rate across major releases.
Senior iOS Developer at Cogna Educação
November 1, 2021 - October 10, 2025Led end-to-end architecture and development of Cogna’s flagship education app (.edu), creating a modular, offline-first platform scalable to 10k+ students. Built a Clean Architecture with RxSwift and Realm; mentored a new iOS team and implemented CI/CD workflows with Fastlane and Bitrise, reducing release cycle time by 40%.
Senior iOS Developer at Neon
March 1, 2020 - October 10, 2025Contributed to Neon’s Loans squad for a mobile banking app used by 30M+ users. Improved performance and reliability of credit application flows; refactored legacy code to improve modularization and reduce crash rates. Mentored junior developers and collaborated with Product, Backend, and QA in agile sprints.
iOS Developer at Mira Educação
April 1, 2019 - October 10, 2025Architected and developed the Mira app from scratch with offline-first capabilities using Realm and GraphQL. Implemented MVVM and Clean Architecture; led technical interviews and onboarding to grow the iOS team; translated educational needs into scalable features with performance and accessibility focus.
iOS Developer at Indice.in
December 1, 2016 - October 10, 2025Developed MobEPI, a safety and compliance app for small companies. Designed intuitive user flows with Core Animation; implemented MVVM architecture and integrated Parse and Firebase for real-time data sync, improving field reporting and equipment tracking.
iOS Developer at Mobi
November 30, 2024 - October 10, 2025Led feature development and architectural improvements on Mobi’s iOS app, used by thousands of subscribers. Implemented 10+ new features using Swift, UIKit and SwiftUI, enhancing reliability and UX across core journeys like billing, usage tracking, and support. Refactored legacy Objective-C modules into Swift, improving maintainability and reducing crash rates by 30% in key screens. Collaborated cross-functionally with Product, Design, and QA in Agile sprints, contributing to backlog grooming, tech planning, and sprint demos.
Senior iOS Developer at Cogna Educação
December 1, 2022 - October 10, 2025Designed and implemented new features for the Ampli (.edu) app using Swift and MVP, ensuring scalability and testability across modules. Leveraged RxSwift and Apollo GraphQL to improve data reactivity and API communication, reducing UI lag and improving responsiveness by 20%. Collaborated with Product, Design, QA, and Backend to ship features aligned with OKRs, participating in roadmap discussions and sprint planning. Streamlined CI/CD workflows by optimizing Fastlane scripts and integrating test coverage thresholds, enabling safer releases and reducing hotfixes. Contributed to system modularization and migration planning as part of post-merger tech consolidation.
iOS Developer at PayPal
September 30, 2022 - October 10, 2025Designed, built, and maintained critical components of PayPal’s iOS app used by 50M+ users, ensuring high availability and performance under heavy transaction loads. Implemented MVVM and SOLID principles to modularize key flows (authentication, payments), improving maintainability. Wrote comprehensive unit tests (XCTest) with 90%+ code coverage for modules handling sensitive data, contributing to a 99% crash-free rate across major releases. Collaborated with distributed teams across time zones to deliver high-quality features in bi-weekly sprints and participated in architecture reviews to ensure secure coding standards and performance improvements.
Senior iOS Developer at Cogna Educação
November 1, 2021 - October 10, 2025Led end-to-end architecture and development of Cogna’s flagship education app (.edu), creating a modular offline-first platform scalable to 10k+ students. Designed a Clean Architecture structure with RxSwift and Realm, enabling seamless offline access and reducing technical debt. Built and mentored a new iOS team (3 engineers): recruiting, onboarding, code reviews, and weekly technical training. Collaborated with Product Managers to prioritize features and roadmaps, aligned with KPIs. Integrated CI/CD workflows with Fastlane and Bitrise, reducing release cycle time by 40% and increasing confidence through automated testing.
Senior iOS Developer at Neon
March 1, 2020 - October 10, 2025Contributed to Neon’s Loans squad on a mobile banking app used by 30M+ users, improving performance and reliability of credit application flows. Refactored legacy codebases and improved modularization, reducing crash rates and enhancing performance of key flows like credit application and approval. Mentored junior iOS developers, delegating tasks, reviewing PRs, and guiding code quality standards. Worked closely with Product, Backend, and QA in agile sprints to deliver features aligned with business objectives and compliance requirements.
iOS Developer at Mira Educação
April 1, 2019 - October 10, 2025Architected and developed the Mira app from scratch, creating an offline-first system with Realm and GraphQL to support teachers and students in low-connectivity environments. Implemented MVVM and Clean Architecture to improve maintainability and scale across municipalities and school networks. Led technical interviews and onboarding, mentoring junior developers through code reviews, pair programming, and architecture discussions. Worked with Product Managers to translate educational needs into features, emphasizing performance and accessibility.
iOS Developer at Indice.in
December 31, 2016 - October 10, 2025Developed MobEPI, a safety and compliance app for managing EPIs in small companies, improving tracking and resource control. Designed intuitive user flows and animated UI using Core Animation, and implemented MVVM to separate concerns. Collaborated with backend teams to integrate Parse and Firebase for real-time data sync, ensuring reliable field reporting and equipment tracking.
iOS Developer at Apple Developer Academy | Senac
January 31, 2016 - October 10, 2025iOS development role within the Apple Developer Academy program, focusing on prototyping apps, UX, performance, and platform conventions.
iOS Developer at Reddit
June 1, 2025 - PresentRemote role on Reddit’s Internationalization squad, developing machine-learning–driven translation experiences to improve accessibility and engagement for global audiences. Implemented A/B experiments to measure translation impact and collaborated with ML, Product, and Backend teams to align execution with localization goals.
iOS Developer at Mobi
November 1, 2024 - October 10, 2025Led feature development and architectural improvements on Mobi’s iOS app used by thousands of subscribers. Implemented 10+ features using Swift, UIKit, and SwiftUI; refactored legacy Objective-C modules to Swift, reducing crash rates by 30% on key screens. Collaborated cross-functionally in agile sprints.
Senior iOS Developer at Cogna Educação
December 1, 2022 - October 10, 2025Designed and implemented new features for the Ampli (.edu) app using Swift and MVP architecture. Leveraged RxSwift and Apollo GraphQL to improve data reactivity and API communication, reducing UI lag and boosting responsiveness by 20%.
iOS Developer at PayPal
September 1, 2022 - October 10, 2025Led development of critical iOS components for PayPal’s app used by 50M+ users. Implemented MVVM, SOLID principles, and comprehensive unit tests (XCTest) with 90%+ coverage, contributing to a 99% crash-free rate across major releases.
Senior iOS Developer at Cogna Educação
November 1, 2021 - October 10, 2025Led end-to-end architecture and development of Cogna’s flagship education app (.edu), creating a modular, offline-first platform. Built a team of 3 engineers, implemented CI/CD with Fastlane/Bitrise, and reduced release cycle time with automated testing.
Senior iOS Developer at Neon
March 1, 2020 - October 10, 2025Contributed to Neon’s Loans squad for a 30M+ user mobile banking app. Refactored legacy code, improved modularization, and enhanced performance for credit application flows. Mentored junior developers and collaborated with cross-functional teams in agile sprints.
iOS Developer at Mira Educação
April 1, 2019 - October 10, 2025Architected and developed the Mira app from scratch with offline-first capabilities using Realm and GraphQL, enabling performance in low-connectivity environments. Implemented MVVM and Clean Architecture; led interviewing and onboarding for new iOS hires.
iOS Developer at Indice.in
December 1, 2016 - October 10, 2025Developed MobEPI, a safety and compliance app for small companies, improving safety resource tracking and field reporting. Implemented MVVM, integrated Parse and Firebase for real-time data synchronization, and enhanced UI with Core Animation.
iOS Developer at Apple Developer Academy | Senac
January 1, 2016 - October 10, 2025As part of the Academy, developed multiple iOS prototypes focusing on UX, performance, and platform conventions; delivered 5+ App Store-ready prototypes and mentored peers in agile, user-centered design practices.
iOS Developer at Reddit
June 1, 2025 - PresentiOS development for one of the world's largest social media platforms. Worked in the Internationalization squad to build ML-driven translation experiences and conducted A/B experiments to improve post visibility across languages. Collaborated with ML, Product, and Backend teams to align execution with internationalization goals and added analytics to measure engagement.
iOS Developer at Mobi
November 1, 2024 - October 10, 2025Led feature development and architectural improvements on Mobi's iOS app, used by thousands of subscribers. Implemented 10+ features with Swift, UIKit and SwiftUI; refactored legacy Objective-C modules to Swift, reducing crash rates by 30% in key screens.
Senior iOS Developer at Cogna Educação
December 1, 2022 - October 10, 2025Designed and implemented features for the Ampli/ .edu app using Swift and MVP. Leveraged RxSwift and Apollo GraphQL to improve data reactivity and API communication, reducing UI lag and improving responsiveness by 20%. Collaborated with Product, Design, QA and Backend; contributed to CI/CD workflows and release planning.
iOS Developer at PayPal
September 1, 2022 - October 10, 2025Designed, built, and maintained critical components of PayPal’s iOS app used by 50M+ users. Implemented MVVM and SOLID, created unit tests with 90%+ coverage, contributing to a 99% crash-free rate. Worked with distributed teams to deliver features in bi-weekly sprints and participated in architecture reviews.
Senior iOS Developer at Cogna Educação
November 1, 2021 - October 10, 2025Led end-to-end architecture and development of Cogna’s flagship education app, .edu, creating a modular offline-first platform. Implemented Clean Architecture with RxSwift and Realm, built and mentored a new iOS team (3 engineers), and collaborated on roadmap with Product. Optimized CI/CD with Fastlane and Bitrise, reducing release cycle time by 40%.
Senior iOS Developer at Neon
March 1, 2020 - October 10, 2025Contributed to Neon’s Loans squad, improving performance and reliability of credit flows in a 30M+ user app. Refactored legacy code for better modularization and reduced crash rates; mentored junior developers and collaborated with Product, Backend and QA in Agile sprints.
iOS Developer at Mira Educação
April 1, 2019 - October 10, 2025Architected and developed the Mira app from scratch, implementing offline-first architecture with Realm and GraphQL. Applied MVVM and Clean Architecture to improve maintainability and scalability; led technical interviews and onboarding for new engineers.
iOS Developer at Indice.in
December 1, 2016 - October 10, 2025Developed MobEPI, a safety and compliance app, with MVVM and real-time sync using Parse and Firebase. Focused on intuitive user flows and offline support for field operations, improving usability and reporting.
iOS Developer at Apple Developer Academy | Senac
January 31, 2016 - October 10, 2025Worked on multiple iOS prototypes using UIKit, AVFoundation and CoreLocation; delivered 5+ app projects from ideation to prototype-ready builds. Integrated third-party SDKs and collaborated in multidisciplinary teams to optimize UX and performance.
Education
Bachelor in Computer Science at Centro Universitário Senac
January 1, 2014 - December 1, 2018Summer Course: Algorithms & Data Structures at Universidade de São Paulo
January 1, 2016 - February 1, 2016Diploma in English Language - C1 at New College Group
October 1, 2022 - October 10, 2025Diploma in Spanish Language - B2 at Expanish Spanish Schools
January 1, 2025 - October 10, 2025Bachelor of Science in Computer Science at Centro Universitário Senac
January 1, 2014 - December 1, 2018Summer Course at Universidade de São Paulo
January 1, 2016 - February 1, 2016Certificate at Apple Developer Academy | Senac
February 1, 2015 - January 1, 2016Technical Degree at Escola SENAI de Informática
January 1, 2012 - December 1, 2013Bachelor, Computer Science at Centro Universitário Senac
January 1, 2014 - December 31, 2018iOS Developer, Apple Developer Academy at Apple Developer Academy | Senac
February 1, 2015 - January 31, 2016Summer Course, Algorithms & Data Structures at Universidade de São Paulo
January 1, 2016 - February 1, 2016Technical Degree, Information Technology at Escola SENAI de Informática
January 1, 2012 - December 31, 2013Bachelor in Computer Science at Centro Universitário Senac
January 1, 2014 - December 1, 2018Summer Course, Algorithms & Data Structures at Universidade de São Paulo
January 1, 2016 - February 1, 2016Technical Degree, Information Technology at Escola SENAI de Informática
January 1, 2012 - December 31, 2013iOS Developer at Apple Developer Academy | Senac
February 1, 2015 - January 1, 2016Summer Course - Algorithms & Data Structures at Universidade de São Paulo
January 1, 2016 - February 1, 2016Bachelor at Centro Universitário Senac
January 1, 2014 - December 1, 2018Technical Degree, Information Technology at Escola SENAI de Informática
January 1, 2012 - December 1, 2013Qualifications
Diploma in English Language - C1
October 1, 2022 - October 10, 2025Diploma in Spanish Language - B2
January 1, 2025 - October 10, 2025Diploma in English Language - C1
October 1, 2022 - October 10, 2025Diploma in Spanish Language - B2
January 1, 2025 - October 10, 2025Diploma in English Language - C1
October 1, 2022 - October 10, 2025Diploma in Spanish Language - B2
January 1, 2025 - October 10, 2025Diploma in English Language - C1
October 1, 2022 - October 10, 2025Diploma in Spanish Language - B2
January 1, 2025 - October 10, 2025Diploma in English Language - C1
October 1, 2022 - October 10, 2025Diploma in Spanish Language - B2
January 1, 2025 - October 10, 2025Industry Experience
Education, Software & Internet, Financial Services, Media & Entertainment, Professional Services, Telecommunications
Experience Level
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