Deniz Egemen Coşkun, Developer in Izmir, Turkey
Deniz is available for hire
Hire Deniz

Deniz Egemen Coşkun

Verified Expert  in Engineering

Full-stack Developer

Izmir, Turkey
Toptal Member Since
July 7, 2022

Deniz is a full-stack developer who began freelancing while at university. He wrote a Loom and Vimeo alternative Chromium extension that improved file upload speeds from 40+ seconds to <10 seconds. Deniz was instrumental in creating a PHP and React app for interpreting and visualizing data used by millions of businesses and developed solutions for technical debts on a product with more than 15 million users. Deniz is known for enhancing the performance of products with a massive user base.


JavaScript, PHP, APIs, React, WebSockets, Optimization, Email, Cron, MySQL...
PHP, Symfony, APIs, React, React Native, Git, GitLab, Symphony, Full-stack...
Java, Behavior-driven Development (BDD), Test-driven Development (TDD)...




Preferred Environment

MacOS, Visual Studio Code (VS Code), GitHub

The most amazing...

...product I've built is a WebSockets server that millions of people benefit from and trust with their business for instantly delivering their updates each day!

Work Experience

Full-stack Developer

2021 - PRESENT
  • Started in the maintenance team, as all newcomers do, and moved to a product team in less than two months. Worked with React on the front-end and PHP on the back-end, mostly on features of the Jotform Tables product.
  • Rewrote (with two other team members) the WebSockets for general use across all Jotform products, with Node.js WebSockets library and Redis using BDD with Cucumber. Reduced WebSockets traffic by around 35% after optimizations.
  • Developed "comments” feature on Jotform Tables, allowing users to write comments on table cells. Coded all of the API with test-driven development. Created every endpoint and possible error path along with their API and unit tests.
  • Designed multiple new tables in the database for new features or optimizing existing code. Refactored and created solutions for various technical debts on a product with more than 15 million users and a codebase going back to 2006.
  • Detected a critical performance and security issue and solved it after meeting with multiple senior engineers, team leads, and architects.
  • Created tools for internal use at Jotform. One of which is a cron job that uses GitHub API to create daily reports about open pull requests. Others are usage graph reports for some of the features added.
  • Mentored part-time members of the team and an intern. Reviewed pull requests of many other colleagues totaling more than 70 pull requests.
Technologies: JavaScript, PHP, APIs, React, WebSockets, Optimization, Email, Cron, MySQL, Redis, Git, GitHub, GitHub API, Testing, Unit Testing, Behavior-driven Development (BDD), Cucumber, Gherkin, API Testing, Node.js, Symphony, Full-stack, HTML, Architecture, SQL, TypeScript, Web Design, REST APIs, REST, User Interface (UI), Full-stack Development, Data Extraction, Amazon Web Services (AWS), QA Automation, CSS, HTML5

Full-stack Developer

2020 - 2021
  • Assisted with the back-end of a company and employee management tool built with Symfony. Designed relational database models and tables for different services to work fast and be storage-efficient.
  • Implemented endpoints while staying true to RESTful API techniques. Followed the MVC pattern and watched for separation of concerns to implement challenging business logic (e.g., complex authorization rules created by a directed graph of roles).
  • Used Elasticsearch and Elasticsearch PHP client Elastica to create complex queries for filtering models.
  • Fixed a system design issue and reduced the product's messaging feature from taking over one second to an instant milliseconds range. This messaging used the Ably Realtime service.
  • Wrote a Loom and Vimeo Record alternative Chromium extension. A 278 MB screencast was shared in less than two seconds after recording. A traditional upload for the same file took 40+ seconds. It shared any size video in less than 10 seconds.
  • Developed an eCommerce app for Android and iOS (both back-end and front-end) using React Native with the given design and API. This app used deep universal links, OneSignal, Facebook login, Redux, nested tab, and stack navigations.
  • Collaborated one-on-one with the product owner to give feedback and ideas about additional features from an engineering and a product view.
  • Developed a desktop app using Electron and TypeScript. This app made API requests, presented a React UI, and utilized computer services (screen recording).
Technologies: PHP, Symfony, APIs, React, React Native, Git, GitLab, Symphony, Full-stack, HTML, iOS, Architecture, Data Scraping, Swift, Android, SQL, JavaScript, TypeScript, Python, Web Scraping, Web Design, REST APIs, REST, Electron, User Interface (UI), Full-stack Development, Data Extraction, Amazon Web Services (AWS), QA Automation, CSS, HTML5, PostgreSQL, Chrome Extensions

Software Developer

2018 - 2020
  • Developed a software-product line project using Java and Redis Pub/Sub architecture with behavior-driven development and Cucumber. It's a smart home software with 30+ pluggable modules that work with each other using events.
  • Wrote tests for an existing software product line of board games (chess, checkers, etc.). Captured gameplay bugs in multiple games. Documented these with information about where and why they occur, with before, after, and expected states of the game board.
  • Created a tool that automatically converts complete event sequences to Gherkin scenarios and automatically converts Cucumber test outputs to a format that makes sense with event sequences.
  • Published work in NAUN International Journal of Computers.
Technologies: Java, Behavior-driven Development (BDD), Test-driven Development (TDD), Cucumber, Gherkin, Redis, Pub/Sub, Event-driven Architecture, New Products, Software, Architecture, SQL, JavaScript, REST APIs, REST, User Interface (UI), Full-stack Development, QA Automation, HTML5

Jotform Tables
A PHP and React app for interpreting and visualizing data submitted by Jotform form users. I worked on the back-end and front-end of multiple features we added to this feature- and user-rich product. I incorporated the Jotform app product into tables, worked on filters, improved data fetching, implemented the comments feature, and fixed many bugs, including rendering issues and data access problems. This is a product that millions of Jotform users trust with their business to reach their customers timely, correctly, and effortlessly.

Werk - Collaboration Tool for Remote Teams

A PHP Symfony and React app for collaboration in remote teams. I was primarily tasked with the back-end development of this project from scratch. I implemented a RESTful API with complex authorization rules, followed MVC patterns, and designed MySQL databases to work fast and storage-efficient. I fixed a WebSockets issue (taking 1+ seconds to send a message) that was taken from another source and actually made it usable. Often, I worked 1-on-1 with the product owner to give feedback and ideas about additional features, not just from an engineering point of view but also from a product view.
2017 - 2021

Bachelor's Degree in Computer Engineering

Izmir Institute of Technology - Izmir, Turkey


REST APIs, React, Node.js, Social Media APIs, GitHub API


GitHub, Git, Cucumber, Cron, GitLab


PHP, JavaScript, SQL, Gherkin, Swift, TypeScript, Python, CSS, HTML5, Java, C, Assembly, HTML


REST, Testing, Unit Testing, Behavior-driven Development (BDD), Test-driven Development (TDD), Event-driven Architecture, Microservices

Industry Expertise

Web Design


Symfony, React Native, Electron, gRPC


MacOS, Visual Studio Code (VS Code), iOS, Android, Docker, Amazon Web Services (AWS), Twilio


MySQL, Redis, Databases, Distributed Databases, PostgreSQL


APIs, Symphony, Full-stack, Full-stack Development, WebSockets, Optimization, API Testing, Architecture, Data Scraping, Web Scraping, User Interface (UI), Data Extraction, QA Automation, Chrome Extensions, Email, Pub/Sub, New Products, Software Engineering, Machine Learning, Development, Non-fungible Tokens (NFT), Software

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.


Share your needs

Discuss your requirements and refine your scope in a call with a Toptal domain expert.

Choose your talent

Get a short list of expertly matched talent within 24 hours to review, interview, and choose from.

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