Daniel Nenkov, Developer in London, United Kingdom

Daniel Nenkov

Software Developer

London, United Kingdom
Toptal Member Since
December 4, 2019

Daniel is adept at digging into complex problems to find innovative solutions that benefit both the company and their clients. Most recently, he has created a digital challenger bank for SMEs, led a team that changed the way people apply for divorce in the UK, and created an award-winning multi-factor authentication platform that was featured in Tech Crunch and WSJ. He's looking forward to tackling his next challenge.

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React Native, React, Apache Kafka, Spring Boot, Spring, Java, SQL, APIs
Ministry of Justice, UK
Node.js, PostgreSQL, Spring Boot, Spring, Java, SQL, APIs
React, Couchbase, Spring Boot, Spring, Java, SQL, APIs


London, United Kingdom



Preferred Environment

Git, IntelliJ, APIs

The most amazing...

...project I have worked on is a challenger bank for small businesses in the UK.

Work Experience

2018 - 2019

Senior Engineer

  • Contributed to the development of Mettle, a standalone SME challenger bank launched by RBS that provides a current account, instant invoicing, and the ability to add receipts to transactions and track expenses from a mobile app.
  • Extended and maintained existing and created new microservices which fit the event sourcing architecture of the Mettle platform.
  • Added features to the React Native mobile banking application.
  • Migrated the event stream to AVRO so we could implement continuous deployment.
  • Extended the automated test suite by introducing consumer-driven contract tests (Pact).
  • Created an interactive dashboard to track business and team OKRs.
Technologies: React Native, React, Apache Kafka, Spring Boot, Spring, Java, SQL, APIs
2017 - 2018

Technical Lead

Ministry of Justice, UK
  • Ensured the divorce microservices fit in the overall high-level design of the reform program. This involved regular meetings with the program architects and communicating design decisions with team members.
  • Created low-level design documents, selecting the right tools and technologies, and made sure that the software released to the public was as robust and secure as it could be.
  • Removed technical impediments and owned the overall sprint outcome.
  • Created new and extended existing microservices to deliver features to citizens, government officials, and solicitors.
  • Led the digital divorce team.
Technologies: Node.js, PostgreSQL, Spring Boot, Spring, Java, SQL, APIs
2015 - 2017

Technical Lead

  • Fully-involved in the architecture, design, and development of new products and features.
  • Wrote a new, modern version of the Callsign dashboard from scratch in React. I managed to phase out the old version of the product iteratively by working closely with product designers to rethink and redesign features and move them to the modern view.
  • Created an extended version of the Callsign Admin REST API which provides a standard interface for onboarding organizations and users into Callsign.
  • Contributed to Callsign On Premise (OP). We were tasked to extract part of the platform to allow deploying it on clients’ premises so that enterprises are in control of their transactional data.
  • Developed Callsign PKI that allows Callsign Cloud to validate OP installations are trusted (CFSSL).
  • Developed EventBridge that provides active unfiltered transmission of events from one site (Cloud or OP) to another.
  • Contributed to the development of Replication Bridge that provides passive filtered replication of changes from one site to another.
  • Architected and developed the first version of a multi-layered security engine that helps enterprises instantly detect and mitigate authentication threats. This later became one of the major selling points of Callsign.
Technologies: React, Couchbase, Spring Boot, Spring, Java, SQL, APIs
2011 - 2015

Senior Engineer

  • Designed, developed, and maintained the payment module in the company's award-winning software solution. The Semafone software provides secure voice transactions for contact centers and retailers taking cardholder not present (CNP) payments.
  • Ensured that the Semafone software is created and maintained using best practices and high security standards so it easily passes the frequent PA DSS certifications.
  • Contributed to the deployment of the Semafone software to clients' on-premise environments.
Technologies: MySQL, jQuery, JavaScript, HTML, Java, SQL, APIs
2008 - 2011

Software Engineer

Business Systems (UK)
  • Designed, built, and supported a platform for call recording and workforce management technologies encompassing quality monitoring, analytics, and workforce management.
  • Designed and developed an asynchronous call storage and archive library which was used to archive call recordings to the company’s internal data storage or to transfer them securely to clients’ premises.
  • Implemented public SOAP and RESTful APIs which were used by the company’s mobile developers and external parties to create and manage conference calls.
Technologies: Firebase, HTML, JavaScript, GWT, Java, SQL, APIs



Forward-looking business bank account.


Real-time AI-driven identity and authentication solutions that confirm the user is really is who they say they are, at work and at home.

Technical Team Lead - Digital Divorce - Ministry of Justice - UK

I spent nine months leading the Digital Divorce Team in the Ministry of Justice in the UK. I was responsible for ensuring that the digital divorce microservices fit in the overall high-level design of MoJ's digital transformation program. I was tasked with creating low-level design documents, selecting the right tools and technologies, and making sure that the software is robust, secure, and follows best practices.



Java, SQL, JavaScript, HTML5, CSS, HTML


Spring, Spring Boot, Spring Security, GWT, React Native


IntelliJ IDEA, Git, IntelliJ




Web, Apache Kafka, Firebase


Spring Data REST, Couchbase, PostgreSQL, MySQL


APIs, Code Architecture


React, jQuery, Node.js


2005 - 2009

Bachelor's Degree in Computer Science

Sofia University - Sofia, Bulgaria