Wael is available for hire
Hire WaelWael Almattar
Verified Expert in Engineering
Architect and Developer
Warsaw, Poland
Toptal member since October 1, 2020
Bio
Wael is a senior software engineer with 10+ years in back-end architecture, APIs, distributed systems, and AI. He builds production AI systems, including multi-agent workflows, RAG, and agentic infrastructure, backed by a track record securing $5+ billion in assets, architecting protocols protecting $300+ million, and running back-end services handling 10+ million requests a day. Wael focuses on performance, scalability, and architecture, and has led teams to deliver on time and within budget.
Portfolio
Offchain Labs
Node.js, Rust, Claude Code, Claude Agent SDK, Codex, Agentic Frameworks...
Space and Time
Solidity, Ethereum Virtual Machine (EVM), EigenLayer, Foundry, Hardhat...
Klarna
Node.js, TypeScript, Amazon Web Services (AWS), Microservices, Apache Kafka...
Experience
- Node.js - 6 years
- API Integration - 5 years
- Go - 4 years
- TypeScript - 4 years
- Microservices - 3 years
- GraphQL - 3 years
- Blockchain - 1 year
- Cosmos SDK - 1 year
Preferred Environment
Amazon Web Services (AWS), SQL, TypeScript, REST APIs, Microservices, Node.js, Go, Ethereum Smart Contracts, Solidity, Cosmos SDK
The most amazing...
...thing I've done was designing and implementing back-end systems that service more than 4 million requests with 100% uptime during Black Friday.
Work Experience
Senior Software Engineer
2025 - 2026
Offchain Labs
- Led a development for token bridge protocol that handles $30 million in weekly traffic.
- Utilised agentic security with AI with continuous high frequently auditing.
- built real-time systems to monitor and support apps deployed on Arbitrum chain.
Technologies: Node.js, Rust, Claude Code, Claude Agent SDK, Codex, Agentic Frameworks, Security, Solidity
Solidity Lead | Web3 Expert
2023 - 2025
Space and Time
- Developed and deployed smart contracts using Solidity with zero critical vulnerabilities in the mainnet.
- Designed and led a development of protocols that secures more than $300 million of assets.
- Spearheaded the integration of advanced cryptographic techniques into the protocol, improving overall system security by 25%.
- Worked with leading zero-knowledge protocols like ZKsync on ZK proofs on the chain and Uniswap, Cube3, and Eigenlayer.
- Developed custom SQL query solidity protocol to serve EVM chains.
- Built and integrated active validator set on EigenLayer, improving the protocol’s staking and slashing mechanisms.
- Coordinated security audits across multiple projects.
- Implemented decentralized oracles and relayers on-chain.
Technologies: Solidity, Ethereum Virtual Machine (EVM), EigenLayer, Foundry, Hardhat, Account Abstraction, Non-fungible Tokens (NFT), TypeScript, Node.js, Concurrency, C++, Concurrent Computing, Full-stack Development, Security, Technical Leadership
Senior Back-end Engineer
2021 - 2022
Klarna
- Worked in a team of eight people to develop and maintain browsers within the Klarna application.
- Took responsibility for the back-end infrastructure of the back-end facing front-end layer and internal service to serve Klarna users.
- Used Node.js and TypeScript to develop and maintain back-end services that handle more than 10 million daily requests.
- Wrote testable, documented code that was highly maintainable.
- Ensured maximum performance, compatibility, and world-class user experience across devices and form factors.
- Stayed up to date on emerging technologies and frameworks.
Technologies: Node.js, TypeScript, Amazon Web Services (AWS), Microservices, Apache Kafka, Redis, Axios, Back-end Development, Solution Architecture, Go, Mobile Back-end, eCommerce APIs, Amazon DynamoDB, Terraform, Low-latency Software, Technical Leadership, Reliability, Identity Verification
Senior JavaScript Engineer
2020 - 2020
Zalando
- Used modern web technologies and frameworks to develop front-end distribution systems for components and libraries across the whole retail center.
- Wrote testable, documented code that was highly maintainable.
- Developed for maximum performance, compatibility, and a world-class user experience across all devices and form factors.
- Collaborated with UI/UX designers to improve usability and accessibility.
- Automated repetitive tasks when possible, using customized scripts.
Technologies: Node.js, TypeScript, Amazon Web Services (AWS), NPM, Microservices, Storybook, Antd, GraphQL, Back-end Development, Full-stack Development, Reliability, Identity Verification
Lead Software Engineer and Architect
2019 - 2020
Anheuser-Busch
- Spearheaded the back-end infrastructure development for a new payment service in the Southern American region with an expected 1 million daily users.
- Designed the overall back-end framework, specifically security, documentation, deployment, testing, etc.
- Implemented an e-wallet, single-page application with React and Webhooks.
- Created checkout components for external usage by customers and published them to the npm library.
- Collaborated with a team of ten developers to implement back-end services by GraphQL.
- Worked with the rest of the squad and external service providers to ensure the back-end services needed in each iteration were delivered.
- Ensured that the pace of delivery was protected by applying best engineering practices.
- Offered a strategic direction on best design practices.
- Provided updates to date documentation at every stage of development.
Technologies: Node.js, TypeScript, React, GRAPH, REST APIs, Apache Kafka, Microservices, Azure, Azure Cloud Services, Kubernetes, NoSQL, MongoDB, Payment APIs, Payment Processing, Fintech, PostgreSQL, Architecture, Back-end Development, Solution Architecture, IT Product Management, Back-end Architecture, Cloud Architecture, IT, AWS Lambda, Amazon DynamoDB, Terraform, Low-latency Software, Full-stack Development, Security
Lead Back-end Developer
2018 - 2019
Yara
- Worked with engineering managers to construct the new team to build a new platform used by the Yara sales team in more than ten countries.
- Constructed a project with TypeScript, GraphQL, and caching, using Redis on the back end and React with hooks and Material-UI on the front end.
- Consulted the business team to draw a reliable roadmap.
- Worked mainly as a back-end developer during my time here.
- Interviewed candidates for permanent roles to continue working on the project.
- Worked with the SRE team to ship deployments with CircleCI, Docker, and Kubernetes.
Technologies: Amazon Web Services (AWS), Unit Testing, Auth0, SQL, Kubernetes, Docker, Material UI, Elastic, Redis, GraphQL, TypeScript, Node.js, Back-end Development, IT Project Management, AWS Lambda, Technical Leadership
Lead Back-end and Microservices Engineer
2017 - 2019
Techloop
- Developed the back end for a platform that serves 100,000 users and 12,000 companies.
- Took responsibility as a lead programmer for the whole back-end infrastructure, including microservices and RESTful APIs.
- Proposed a simplified but scalable system architecture that is being used at the moment in the production environment.
- Introduced GraphQL to the platform and worked with the front-end team to integrate it.
- Used automated solutions to accelerate the development process.
- Extended the existing API with more features and functionalities.
- Tracked tasks, features, and bugs with Jira and Asana.
- Implemented a data-driven approach to support the marketing and sales teams.
- Created a one-page application using React and custom components on top of MUI v4.
- Worked with the business development manager on breaking down new business models into realistic technical tasks with a clear roadmap.
Technologies: Auth0, SQL, PostgreSQL, RESTful Development, REST APIs, APIs, Cron, Git, Koa, AMQP, RabbitMQ, React, GraphQL, Microservices, Go, Node.js, Google Ads API, Linux, Full-stack Development
React Developer
2017 - 2017
International Committee of the Red Cross (via Iosbar Blue Infinity)
- Developed a custom CRM system for the International Committee Red Cross.
- Tracked features and fixed bugs using Microsofts TFS platform and Microsoft PBI. The platform has been launched successfully and has been in production used internally by ICRC.
- Provided full unit testing and clear documentation.
Technologies: Git, Amazon Web Services (AWS), Jest, TypeScript, Node.js, React, Full-stack Development, Identity Verification
Full-stack Developer
2017 - 2017
Dether.io
- Implemented a single-page, live-map platform to show users and shops.
- Extended the API for the Dether.io platform with a couple of endpoints.
- Formulated and documented technical architecture, components, and strategies for mitigating technical challenges.
Technologies: Git, React Native, Google Maps, Mapbox, Redux Form, Jest, Redux, React, Node.js
Full-stack Developer
2016 - 2017
VariSolutions
- Worked part-time with the core team to grow the main back-end server using Node.js.
- Implemented new features and pages using React for A/B testing software.
- Wrote unit, end-to-end, and integration tests using Mocha and Jest.
- Optimized the performance by moving aggregated data to Redis server storage.
- Implemented an A/B testing solution to determine the better-performing variations.
Technologies: Mocha, Git, Heroku, Redux, Testing, Jest, Express.js, Redis, Node.js, React
Software Engineer
2015 - 2016
Globe IT
- Designed a complete tracking system for GPS tracking devices with a live real-time dashboard using Node.js, Socket.IO, and AngularJS.
- Created and designed a decoder server to handle a GPS binary device’s data and send commands.
- Optimized a web application's speed and data structures by combining Memcached and MySQL databases.
- Led the API development of a new eCommerce/digital platform (PHP and Node.js).
- Designed a dashboard along with a complete solution for a chat module for an eCommerce project using PHP and AngularJS.
- Maintained existing eCommerce and digital applications to meet the ever-evolving demands of the business (PHP).
- Implemented an online payment system for eCommerce services.
- Developed from scratch an interactive web conference video platform that hosted video rooms with text and voice capabilities using WebRTC, Socket.IO, and jQuery.
- Used AngularJS as the development framework to build a dashboard, a single-page application, and a more interactive front end.
- Developed a web-scraping application along with the entire server-side application using Python.
Technologies: SQL, Git, C++, Loopback, WebRTC, Python, MySQL, Zend Framework, jQuery, CSS, PHP, Redis, Express.js, Socket.IO, AngularJS, Node.js, Back-end, Linux
Web Developer Intern
2014 - 2014
Mamania.pl
- Worked on various projects where more experienced, senior developers guided me.
- Integrated and tested an online payment system to the eCommerce platform.
- Worked primarily as a full-stack developer as part of my bachelor's degree thesis.
Technologies: CSS, SQL, JavaScript, PHP, Zend Framework
Experience
Back-end Infrastructure for Two APIs and Six Microservices
https://techloop.ioAs the lead back-end developer, I was responsible for rewriting one API and extending the features on the other one along with six microservices connected to third-party solutions. I introduced scalable, modern technologies implemented and used nowadays in production to serve more than 100,000 daily users.
Lead Back-end Consultation
I proposed and led the development of a back-end infrastructure for a nutrition plan generation platform used by the sales team at an established fertilizer-producing company (established in 1905) valued at $8 billion. The back end was integrated with an already existing agronomical engine and SSO authentication service.
GEO2 | Live Tracking System for Cars, People, or Animals
http://geo2.pl/For this project, I first built a back-end server that decodes binary signals from geolocation devices. Then I implemented a single-page application to show real-time data on maps. The application was designed both for web and mobile devices. The platform supports multiple users per partner and also has an online payment system.
The devices and platform are used by more than 20 partner companies.
The devices and platform are used by more than 20 partner companies.
X Twitter Real-time AI Sentiment Charts
https://x-realtime-tweets.com/X Realtime is a dashboard that reads X/Twitter sentiment from the accounts that move markets, scoring every post bullish, bearish, or neutral, categorizing the news, and rolling it into live per-asset signals the second it lands. It also offers event search across a full historical archive and a live geotagged headline map, so you can see market mood shift before it moves.
Education
2016 - 2017
Joint Master's Degree in Space Science and Technology
Université Paul Sabatier Toulouse III - Toulouse, France
2016 - 2016
Completed Credits Towards a Joint Master's Degree in Space Science and Technology
Luleå University of Technology - Kiruna, Sweden
2015 - 2016
Completed Credits Towards a Joint Master's Degree in Space Science and Technology
The Julius Maximilians University of Würzburg - Würzburg, Germany
2012 - 2015
Bachelor's Degree in Computer Science
Warsaw University of Technology - Warsaw, Poland
Certifications
NOVEMBER 2012 - PRESENT
Fifth Place in a Collegiate Programming Contest
ACM
SEPTEMBER 2010 - PRESENT
Bronze Medal
International Olympiad in Informatics (IOI)
Skills
Libraries/APIs
Node.js, React, Slack API, Socket.IO, React Redux, Google Ads API, jQuery, WebRTC, Redux Form, Google Maps, AMQP, Objection.js, Segment.io, REST APIs, Antd
Tools
Git, RabbitMQ, Cron, CircleCI, Slack, Terraform, Elastic, Mocha, GIS, Auth0, NPM, Claude Code, Claude Agent SDK, Codex
Languages
GraphQL, TypeScript, C++, JavaScript, HTML, Go, SQL, C, Python, PHP, CSS, Solidity, Rust
Frameworks
Koa, AngularJS, Express.js, Zend Framework, Loopback, Jest, Redux, React Native, Material UI, Angular, Cosmos SDK, Tendermint, Hardhat, Agentic Frameworks
Paradigms
Microservices, Microservices Architecture, RESTful Development, Model Context Protocol (MCP), Unit Testing, Automation, Management, Testing, Back-end Architecture
Platforms
Amazon Web Services (AWS), Algolia, HubSpot, AWS Lambda, Linux, Heroku, Mapbox, Docker, Kubernetes, Apache Kafka, Azure, Blockchain, EigenLayer
Storage
Amazon DynamoDB, Redis, MySQL, PostgreSQL, Azure Cloud Services, NoSQL, MongoDB
Other
APIs, Back-end, Architecture, Back-end Development, API Integration, Full-stack Development, Security, Identity Verification, Agentic AI, Computer Science, Algorithms, Web Programming, Software Engineering, Data Structures, RESTful Microservices, Code Auditing, Cryptography, Low-latency Software, Concurrency, Technical Leadership, Reliability, LangChain, Machine Learning Operations (MLOps), Machine Learning, Data Analytics, Mobile App Development, Space Dynamics, Communication, Custom Instruments, Space Physics, Artificial Intelligence (AI), Electronics, Astrophysics, Image Processing, Microcomputers, Intercom, Full-stack, GRAPH, Payment APIs, Payment Processing, Fintech, Storybook, Axios, Solution Architecture, Ethereum Smart Contracts, eCommerce, Mobile Back-end, eCommerce APIs, IT Product Management, Cloud Architecture, IT, IT Project Management, Ethereum Virtual Machine (EVM), Foundry, Account Abstraction, Non-fungible Tokens (NFT), Concurrent Computing
Collaboration That Works
How to Work with Toptal
Toptal matches you directly with global industry experts from our network in hours—not weeks or months.
1
Share your needs
Discuss your requirements and refine your scope in a call with a Toptal domain expert.
2
Choose your talent
Get a short list of expertly matched talent within 24 hours to review, interview, and choose from.
3
Start your risk-free talent trial
Work with your chosen talent on a trial basis for up to two weeks. Pay only if you decide to hire them.
Top talent is in high demand.
Start hiring