Guillermo Waitzel, Developer in Buenos Aires, Argentina
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Guillermo Waitzel

Verified Expert  in Engineering

APIs Developer

Buenos Aires, Argentina
Toptal Member Since
November 14, 2013

Guillermo is an outstanding software engineer with 12+ years of experience developing world-level applications. He is capable of designing and deploying complete apps from 0 to 1. His achievements range from building apps rated with 4.9 stars on the App Store to receiving several Apple features. Guillermo owns what he builds, commits, and works hard to achieve success. He leads and scales teams but is also a great team player.


Domain Money
Swift, APIs, SwiftUI, UIKit, Xcode, Git, WebAuth, SQL, MySQL
Goldman Sachs
Swift 2, iOS, Xcode, Location Services, Swift 3, Realm, Push Notifications...
Clarity Money
Swift 2, iOS, Xcode, Location Services, Swift 3, Realm, Push Notifications...




Preferred Environment

Swift, Git, Xcode, iOS, SwiftUI, UIKit, APIs

The most amazing...

...thing I developed is Marcus by Goldman Sachs. The bank's consumer banking app—has several times awarded iOS with average ratings of 4.9 in the App Store.

Work Experience

Lead iOS Engineer

2021 - 2022
Domain Money
  • Built the app's trading feature, allowing users to buy, sell, and swap stocks or crypto inside the platform.
  • Built the transfers feature. This enables users to deposit or withdraw money to and from external accounts linked using "Plaid." It also includes the management of external accounts.
  • Developed the "strategies" feature. A set of investing strategies that include a combination of assets (stocks and crypto) within a certain level of desired risk and exposure.
  • Created an onboarding wizard which showcased and helped new users grasp all the app's features, allowing them to take immediate action (link an account, buy an asset or strategy, etc.).
  • Created the KYC of the app, a set of screens and forms needed for onboarding a user into the platform. The order of the screen is server-based, allowing for further customization.
Technologies: Swift, APIs, SwiftUI, UIKit, Xcode, Git, WebAuth, SQL, MySQL

Lead iOS Engineer

2018 - 2021
Goldman Sachs
  • Led and launched the "Savings account" feature, which provided useful information, transactions, several charts, linking external accounts, and the ability to transfer from and to the savings account.
  • Led and mentored a team of two people. I was in charge of the "Savings and Checking" team. I conducted interviews and presented the "Checking Initiative" in a quarter opening meeting to an audience of 100 people.
  • Redesigned the home feed with a custom collection view layout that displayed auto-sizing tiles. This allowed the team to focus on building the tile's content and seemingly integrate them into the app.
  • Expanded the "Checking account" feature. This included managing the checking account (similar to savings) and debit card management.
  • Leveraged the card management feature from "Checking" to be used with external cards through the service Marqeta. Our card management feature was excellent, which allowed us to integrate external cards in two weeks.
Technologies: Swift 2, iOS, Xcode, Location Services, Swift 3, Realm, Push Notifications, Swift, GraphQL, Model View ViewModel (MVVM), UIKit, SwiftUI

iOS Engineer

2016 - 2018
Clarity Money
  • Launched the V1.5 of the app, which improved in many aspects and achieved an outstanding 4.9 stars in the App store, becoming the main competitor to Mint.
  • Integrated Plaid to link external accounts, display their transactions, and gather helpful information for the user.
  • Implemented the "Savings account" feature. It allowed users to save for a goal and make recurring investments.
  • Built more than five tiles and features within the app, including "Savings," "Credit Cards," "Credit Score," "Transactions," etc.
  • Oversaw the animations and UI flair within the app. Implemented the main loading animations and success particle systems.
Technologies: Swift 2, iOS, Xcode, Location Services, Swift 3, Realm, Push Notifications, Model View ViewModel (MVVM), Swift, UIKit, SwiftUI

Lead Developer

2016 - 2016
  • Developed an Instagram-like social network. I built and deployed the full app, including login, profile management, new posts feature, and reporting.
  • Created an innovative tag system for each picture, with a creative UI that allowed several tags to be placed near locations.
  • Delivered iOS architecture using VIPER-inspired router and MVP concepts.
  • Developed a deep-link URL scheme for inter-app communication and better user experience.
  • Created a mentions and notifications system on different parts of the app.
Technologies: Parse, iOS, Swift

Lead Developer

2016 - 2016
  • Developed the back-end of a social network.
  • Developed the UI/UX of a social network.
  • Integrated AWS S3 to the social network storage.
  • Implemented server architecture in AWS.
  • Set up generic graphic artifacts that are used in development of modern UI.
Technologies: Node.js, iOS

Lead Software Engineer

2015 - 2016
  • Redesigned server-client architecture.
  • Redesigned the server database.
  • Improved system stability/security.
  • Supported different types of discounts.
  • Supported synchronization of the POS with the server and app, allowing to manually update tickets from POS.
Technologies: JavaScript, Swift, Objective-C

Lead Software Engineer

2014 - 2015
  • Created the architecture for a cloud-based contact management application.
  • Developed a full messaging system with the ability to share media content such as photos, videos, GIFs, and audio.
  • Implemented a dynamic notifications system, which can be adapted server-side to new formats or information types.
  • Integrated the iOS native address book into an existing app, enabling users to modify information in a different way.
  • Implemented efficient graphic effects for enhancing user experience, such as complex animations, compounded blur, image composition, and more.
Technologies: QuartzCore, Data Protection, Core Bluetooth, Core Data, iOS, Objective-C

iOS and Mac OS Developer

2010 - 2014
Esquilax Games
  • Created an OpenGL-based graphics engine supporting 2D and 3D rendering.
  • Implemented the iOS game Climber Brothers.
  • Created a .OBJ (3D models) loader and parser for rendering 3D meshes.
  • Developed the AI for card games featuring a variable level of skill.
  • Created a step by step animation algorithm integrated with the Cocoa Framework.
  • Designed a custom level creation tool for the app Climber Brothers.
  • Added support for sharing content on social networks in all of the company's games.
  • Added realistic physics simulation via integration of Box2D.
  • Incorporated SVG support for curve creation and terrain design.
  • Created a smoothing algorithm using SVG curves and approximation.
  • Implemented rope physics using constraints and Newtonian mechanics.
  • Designed and implemented a PVP multiplayer environment for a battle game.
  • Created a particle system including generation of radial and gravity particles.
  • Created the Battle Rush game.
  • Implemented a radio streaming app.
  • Developed a server-client framework for displaying animations simultaneously on different devices.
Technologies: Box2D, OpenGL ES, C++, C, Objective-C

iOS Developer

2013 - 2013
Wuzy INC
  • Integrated Stripe as a payment system.
  • Integrated OpenMaps into the application.
  • Designed a GPS-like route finder to display on screen.
  • Implemented signup/sign-in UI for Vines and customers.
  • Implemented custom maps annotations for improving UX.
Technologies: PubNub, Stripe, Objective-C, iOS

iOS Developer

2012 - 2012
  • Developed an app, Vale Puerto, for showing company port facilities in Argentina.
  • Created an app, Vale, for displaying company facilities in Argentina.
  • Supported image and video display via AVFoundation.
  • Designed a custom map interface showing different spots in the VALE facilities.
  • Implemented support for efficient scrolling around the Vale app.
Technologies: Objective-C

iOS Developer

2012 - 2012
Portegno Apps
  • Created the Crazy Hairstyle Studio app.
  • Created a base framework for editing hairstyles in a realistic hairstyle salon app.
  • Built a multi-shading tool for blurring, coloring, and efficient rendering of images.
  • Added features for camera support, photo editing, and screenshot export to a game.
  • Added online synchronization for user-created products.
  • Designed and implemented a virtual canvas to support multiple devices.
  • Created an anchor and multi-point manipulation system for displayed objects.
  • Added support for real-time image editing by rendering images to textures.
Technologies: Objective-C

iOS Developer

2011 - 2012
Webetico SNC
  • Supported communication with an AS400 for an iOS app.
  • Supported multithreaded loading of images to display in a catalogue.
  • Developed a framework for synchronizing local data with server data.
  • Designed and implemented a custom grid for displaying data.
  • Supported image synchronization on demand.
  • Created a trivia game that allowed possible customers to their contact information.
  • Created a multi-language app for a museum displaying information about museum exhibits.
  • Created a CRM app allowing customers to place orders online and offline.
Technologies: Objective-C

Marcus by Goldman Sachs
Marcus by Goldman Sachs offers personal finance tools to help you save, borrow, and invest. Grow your money with a high-yield online savings account, high-yield CDs, and no-penalty CDs. Pay down high-interest debt with a no-fee personal loan. Automate your investing with Marcus Invest and connect thousands of financial institutions to Marcus Insights' free tools and trackers that help you organize and optimize your finances.

Domain Money
Investing solved for you: Invest in stock and crypto portfolios. Trade individual stocks or crypto assets all in one place. See the markets clearly with our proprietary dashboard and understand them like never before with Signal, our pro-level market indicators. Get critical data, such as exchange funds flow, blockchain project health, social sentiment, and more. We support over 4,000 stocks and ETFs and 49 cryptocurrencies, including Apple (AAPL), Tesla (TSLA), Bitcoin (BTC), Ethereum (ETH), Solana (SOL), Polygon (MATIC), Uniswap (UNI), Bitcoin Cash (BCH) and more.

Clarity Money

‎Take control of your budget and expenses with Clarity Money. We use machine learning to analyze your personal finances and help you make smart decisions about your money, from budgeting to saving to spending.


This is a social network aimed at university students. It displays typical social information, articles of interest, and news, allowing students to interact and be part of the community campus. I solely developed the full app and back-end server in Node.js.


Atmospheir is a social address book that lets your contacts update their information for you. Create a personalized ID (like a Twitter handle), share it with friends to connect, and exchange as much contact and social network information as you want. We'll notify you and update your address book whenever your contacts update their information. Just sit back, relax, and enjoy up-to-date contacts and free text, voice, photo, GIF, and location messaging with every Atmospheir connection.


An Uber-like system specifically designed for attending vines and events, finding them, and getting discounts on those associated Vines and places.


QuickEats is an iPhone application that revolutionizes the way people order and pay at their favorite restaurants. QuickEats allows customers to browse the menu, place an order, and pay straight from their phones

Climber Brothers

An iOS rope physics puzzle game.

Battle Rush

An infinite multiplayer PVP runner game.

Crazy Hair Studio

A realistic hairstyle simulator.


A Spanish card game for iOS.


Phelo is a social network for sharing pictures. The concept is simple, tag the world around you. Every person, place, and thing. It’s all about expression. Go beneath the surface and truly discover why a picture is worth a thousand words. We all know filters and photo-liking are cool, but what if you could like, share, and comment on individual aspects of a picture? Now that's crazy.

• Tag anything within a picture and associate it with a profile,
hashtag, or location
• Add links to your tags
• Share photos with your friends
• Like, share, or comment on any tag
• Discover tags from around the world

Escoba de 15

A Spanish card game with single and multiplayer features.


A jewelry catalogue iPad application for Cielo Venezia.
2006 - 2010

Bachelor's Degree in Software Engineering

Universidad Tecnológica Nacional - Buenos Aires, Argentina


Node.js, Parse SDK, Facebook SDK, OpenGL ES, OpenGL, Stripe, PubNub


Xcode, TestFlight, Git, AWS ELB, AWS SDK, Mongoose


Core Data, iPhone SDK, iOS SDK, Box2D, SwiftUI, UIKit, Unity, QuartzCore, Cocoa, JSON Framework for Objective-C, Core Bluetooth, Express.js, ADO.NET


Model View ViewModel (MVVM), Model View Controller (MVC), Object-oriented Programming (OOP), Design Patterns, Model View Presenter (MVP), Agile Software Development, Concurrent Programming, Functional Programming


Swift, Objective-C, SQL, C, C++, C#, T-SQL (Transact-SQL), GraphQL, Swift 4, Swift 2, Swift 3, JavaScript


iOS, Parse, Amazon EC2, Amazon Web Services (AWS)


Realm, Oracle PL/SQL, MongoDB, MySQL, Amazon S3 (AWS S3), Databases


Software Engineering, APIs, Data Protection, Back-end, Location Services, Push Notifications, Low-level Programming, GRDB, Securities, WebAuth

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