Jonah Fox, Developer in Aarhus, Denmark
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Jonah Fox

Verified Expert  in Engineering

Software Developer

Aarhus, Denmark
Toptal Member Since
January 6, 2020

Jonah is a highly skilled technologist with 20 years of experience in startups and corporations across various sectors, including gaming, health, finance, and music. He has expert-level proficiency in many software technologies, including full-stack development, UX, product development, web and mobile, and server. Jonah thrives on solving business problems quickly through the pragmatic use of technology.


ChatGPT, Svelte, MongoDB, Text to Speech (TTS), Google AI Platform, LangChain
React, OpenAI, Text to Speech (TTS)
Down the Garden Path
Artificial Intelligence (AI), Pinecone, Google Cloud SDK, Text to Speech (TTS)...




Preferred Environment

Xcode, Git, Visual Studio Code (VS Code), MacOS, SQL, Artificial Intelligence (AI), TypeScript, Virtual Reality (VR)

The most amazing...

...project I've coded is KRFT, a completely new modular way to make music on the iPad featured as App of the Day multiple times by Apple.

Work Experience

Lead Engineer

2023 - PRESENT
  • Created the website Fablefish which makes fun and exciting stories using AI based on user prompting. It uses novel methods to give the stories a good structure. Children, in particular, enjoy creating wild and imaginative stories.
  • Added Text to Speech (TTS) by Google Cloud so young children can enjoy listening to the stories.
  • Added an interactive mode where users can participate in a "choose your own adventure."
Technologies: ChatGPT, Svelte, MongoDB, Text to Speech (TTS), Google AI Platform, LangChain

Lead Engineer

2023 - PRESENT
  • Developed a platform to allow authors to use the latest text-to-speech products (e.g., Elevenlabs) to create audiobooks, giving them complete control of the process and producing the highest quality media.
  • Published various audiobooks using the Project Gothenburg books, e.g., The Awakening by Kate Chopin.
  • Used Whisper API to convert the speech to the text and grab the timestamps. This enables the platform to allow the user word-level regeneration and nuance or hints to the AI where needed.
Technologies: React, OpenAI, Text to Speech (TTS)

AI and Full-stack Programmer

2023 - PRESENT
Down the Garden Path
  • Developed a system to automatically ingest text/audio/video content and create OpenAI embeddings that can be used to query this content. Clients can then use the data to create custom with GPT based on their existing media quickly.
  • Contributed to the main part of the project: data extraction that converts video to audio and then uses Google Cloud Platform to convert the speech to text. It is then embedded in the Pinecone database for later retrieval.
  • Worked on the second part of the project: the retrieval of this data and synthesis of new media depending on the client's requirements. This is done by querying the Pinecone database and prompting GPT3 correctly.
Technologies: Artificial Intelligence (AI), Pinecone, Google Cloud SDK, Text to Speech (TTS), Speech to Text, Streaming Data, Node.js, Python, Vercel, OpenAI GPT-3 API, Amazon S3 (AWS S3), Web Architecture, Web Development, Chatbots, Software Development, OpenAI GPT-4 API, Back-end, Front-end Build Tools

iOS or Android Developer

2023 - 2023
BDS Digital Health Solutions GmbH
  • Established numerous audio issues using a streaming stethoscope and fixed them all.
  • Devised and implemented an audio filter to improve the audio quality by collaborating with the medical team.
  • Oversaw replication of iOS fixes and functionality into Android.
Technologies: Medical Devices, iOS, Audio, Android, Mobile Development, Audio Streaming, Startups, Audio Processing

Platform Architect and Front-end Developer

2020 - 2022
  • Designed and developed the entire back-end architecture for the VR platform, turning it from a single-player experience into a social multiplayer experience.
  • Built the front-end admin user interface for managing user data and later opened it up to the public to manage their interfaces.
  • Collaborated with the game developers to integrate the back end and also oversaw the development of multiplayer peer-to-peer live jamming.
Technologies: Node.js, Svelte, MongoDB, MongoDB Atlas, Amazon S3 (AWS S3), Front-end, Data Analytics, Leadership, Web Architecture, Web Development, API Integration, Software Development, Virtual Reality (VR), Front-end Build Tools, DevOps, Startups

Senior React Native Developer

2021 - 2021
  • Was brought in to troubleshoot and fix a collaborative music-playing application built in React Native with hooks for Firebase. The existing build had many issues that I diagnosed and fixed, resulting in a quality product.
  • Diagnosed and solved the main issue: the React hooks implementation was slowing down the interface.
  • Diagnosed and resolved the second issue: the implementation of the audio player was buggy. I replaced it with a custom native version that avoided all the issues.
Technologies: React Native, Firebase, Swift, iOS, Audio, Analytics, Leadership, Web Development, Software Development, Mobile UI Design, Back-end, Image Processing, Streaming, Front-end Build Tools, User Experience (UX), Cross-platform


2012 - 2021
Studio Amplify
  • Built several music-making apps featured on the App Store using JavaScript, Objective C, C++, and DSP.
  • Created a custom data management system for a members club using Node.js and MySQL.
  • Created a TikTok-style social video creation network using Firebase, C++, and JavaScript.
  • Built two meditation/mindfulness apps called COSM and Beathesonic. Both were featured as "App of the Day" by Apple.
  • Created a powerful video processing library using GLSL for use with iOS.
  • Built a machine-learning face-swapping service for the Cats movie. This was used to promote the film by letting users create their own "cats" for sharing.
Technologies: MongoDB, Node.js, React Native, OpenGL, JavaScript, Objective-C, C++, Full-stack, APIs, SQL, Agile Software Development, MEAN Stack, Three.js, HTML5, Databases, TypeScript, Technical Leadership, CTO, Figma, Proof of Concept (POC), Online Payments, PostgreSQL, Payment APIs, Video Streaming, iMessage, Architecture, Stripe, Audio, Audio Streaming, Analytics, Data Analytics, Material UI, Leadership, Web Architecture, Web Development, API Integration, Software Development, UI Design, User Interface (UI), Mobile UI Design, Back-end, Networking, Video Players, Video Processing, Video & Audio Processing, Image Processing, Photo Editors, WebSockets, HTTP Live Streaming (HLS), Streaming, REST APIs, JUCE, Electron, Hardware, Bluetooth, Front-end Build Tools, User Experience (UX), DevOps, Agile, Windows, Audio Processing, Audio Drivers, Product Licensing


2004 - 2010
Parker Fox
  • Built a financial management system that processed $100 million of payments a month.
  • Developed and optimized application forms using analytics.
  • Hired, trained, and mentored 10+ members of staff.
  • Built a bespoke eCommerce system and back end for a jewelry store.
  • Scoped, specced, built, and managed customer relationship management system.
  • Built a social network for healthcare practitioners.
Technologies: MySQL, Ruby on Rails (RoR), Ruby, CSS, HTML, JavaScript, SQL, C#, C, Full-stack, APIs, MongoDB, Agile Software Development, MEAN Stack, Python, HTML5, Databases, Technical Leadership, CTO, PHP, Games, Minimum Viable Product (MVP), Proof of Concept (POC), Chatbots, Finance, D3.js, Online Payments, PostgreSQL, Payment APIs, Architecture, Stripe, Search Engine Optimization (SEO), Leadership, Web Architecture, Non-performing Loans (NPL), API Integration, Software Development, Networking, Video Players, Video & Audio Processing, REST APIs


2006 - 2007
Global Gaming
  • Built and oversaw sports betting markets arbitraging prices between different events and platforms.
  • Managed stakeholder management and investor relations.
  • Managed team building trading software system and monitoring system.
  • Researched and developed profitable and scalable trading strategies.
  • Built speculative systems for exploring carbon credits markets.
Technologies: Microsoft SQL Server, C#, APIs, SQL, Agile Software Development, Python, Databases, Web Scraping, Scraping, Technical Leadership, CTO, Minimum Viable Product (MVP), Proof of Concept (POC), Finance, Online Payments, PostgreSQL, Payment APIs, Architecture

Audio Programmer

2000 - 2002
Sony Computer Entertainment Europe
  • Built the first audio engine for Sony PS2 using the Japanese manual.
  • Contributed to sound programming for the PS2 game Dropship.
  • Worked directly with the product lead and musicians to implement game/audio engine infrastructure.
Technologies: DSP, C++, APIs, Databases, Games

Mathematical Analyst

1994 - 1995
Hydro International
  • Provided unique mathematical analysis for a tipping gate mechanism that led to a Queen's Award for the Environment.
  • Completed mathematical modeling and comparison with physical measurements of forces on a 90-degree drop pipe.
  • Oversaw production and research and development (R&D) of the "linear cleanse" version of the product.
Technologies: MathScript

Cosm – iOS App

Cosm lets you quickly and easily create your own ambient soundscape to relax and refocus. We believe music and creativity have an important role to play in improving our minds and souls.

We conceived and built Cosm, an iOS app that won the App Store Award: App of the Day and has a 4.8 out of 5 stars rating.

KRFT – iOS App

KRFT is a modular instrument for expressive music production that we built to challenge the two-decade-old paradigm of the multi-track DAW. Designed from the ground up with a focus on live experimentation and expressive interactions, KRFT will inspire you to make music that would normally be out of reach.

This app was featured as App of the Day with a 4.7 out of 5 stars rating and
was featured in "App Store 2017: New Apps we Love in 50+ Countries."

ChillScape – Sonic Meditation

ChillScape is a tool for quick bursts of mindfulness and anxiety relief. Lose yourself in the mesmerizing graphics and beautiful soundscape that are both inspiring and calming. It can be used to relax, focus the mind, or filter out unwanted distractions such as pain or negative thoughts.

The app was featured in "App Store 2017: New Apps we Love in 50+ Countries".

PatchXR – Musical VR

PatchXR is a Facebook-funded VR music app for Oculus. I was the platform architect specifying and building the back end to enable players to interact socially, both live and offline. It's currently doing very well in the Store.

BreatheSonic – Learn to Breathe

A ReactNative app for helping people to breathe using various techniques such as "box breathing" and "478". I conceived, designed, and built the whole project.

The app is very popular with users with an average of 4.9 out of 5.

"Beautiful and engaging app that has really helped me through some stressful work days. The music and ambient sounds are amazing without being distracting and the art and colors are stunning. Amazing job." - user
2003 - 2004

Master's Degree in Electroacoustic Composition

City University - London, England

1996 - 1999

Bachelor of Science Degree with First Class Honors in Physics

Imperial College London - London, England


OpenGL, Node.js, React, WebGL, WebRTC, REST APIs, MobX, Three.js, Stripe, D3.js


Xcode, Photo Editors, Front-end Build Tools, ChatGPT, Adobe Photoshop, Git, Figma, MongoDB Atlas, Google AI Platform


React Native, Svelte, Material UI, Electron, Ruby on Rails (RoR), JUCE


SQL, Ruby, C++, JavaScript, Objective-C, HTML, C, CSS, HTML5, C#, Lua, Python, TypeScript, Swift, PHP


MEAN Stack, Mobile App Design, Mobile Development, Web Architecture, UI Design, Mobile UI Design, DevOps, Cross-platform, Microservices, Agile, Agile Software Development, Search Engine Optimization (SEO)


iOS, Firebase, Mobile, Windows, Android, Linode, Amazon Web Services (AWS), DigitalOcean, MacOS, Visual Studio Code (VS Code), Web, Google Cloud SDK, Vercel


MySQL, Databases, PostgreSQL, MongoDB, Google Cloud, Microsoft SQL Server, Amazon S3 (AWS S3)


DSP, Front-end, Digital Signal Processing, Full-stack, APIs, SvelteKit, Web Scraping, Scraping, Technical Leadership, CTO, Full-stack Development, Minimum Viable Product (MVP), Proof of Concept (POC), Finance, Online Payments, Payment APIs, Video Streaming, Architecture, Audio, Audio Streaming, Analytics, Data Analytics, Leadership, Web Development, API Integration, Cloud, Cloud Services, Software Development, User Interface (UI), Back-end, Networking, Video Players, Video Processing, Video & Audio Processing, Image Processing, WebSockets, Streaming, User Experience (UX), Startups, Native Mobile Apps, Audio Processing, Music Composition, Artificial Intelligence (AI), Games, Chatbots, Non-performing Loans (NPL), OpenAI GPT-4 API, HTTP Live Streaming (HLS), Virtual Reality (VR), Hardware, Bluetooth, Audio Drivers, Product Licensing, MathScript, iMessage, Mathematics, Physics, Pinecone, Text to Speech (TTS), Speech to Text, Streaming Data, OpenAI GPT-3 API, Medical Devices, OpenAI, LangChain

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