Nikolay is available for hire
Hire NikolayNikolay Konovalov
Verified Expert in Engineering
Software Engineer and Developer
Warsaw, Poland
Toptal member since September 1, 2026
Bio
With experience in software engineering, Nik builds and modernizes SaaS, fintech, edtech, eCommerce, and security-critical products. At Codility, he owned the identity and access domain behind 200+ endpoints and addressed 20+ audit findings. He works end-to-end, from architecture and back-end systems to polished React/Vue interfaces and AWS infrastructure, using Ruby, TypeScript, PostgreSQL, Docker, and Terraform.
Portfolio
Codility
Python, Django, React, Next.js, FastAPI, PostgreSQL, Terraform, Authentication...
Stash
CI/CD Pipelines, Datadog, Docker, JavaScript, Kubernetes, Kafka, Kotlin...
Amitree
Docker, Ember.js, Google API, Heroku, Mailchimp, Mixpanel, PostgreSQL, Redis...
Experience
- Ruby on Rails - 6 years
- Ruby - 6 years
- Payment Gateways - 6 years
- React - 5 years
- Identity & Access Management (IAM) - 4 years
- Performance Optimization - 4 years
- Web Security - 4 years
- Python - 3 years
Preferred Environment
Terraform, Amazon Web Services (AWS), PostgreSQL, Redis, Apache Kafka, Ruby, JavaScript, Python, React, Node.js
The most amazing...
...OSS system I'm building is an intent graph connecting product specs to code and evidence, so teams can understand software quicker.
Work Experience
Senior Software Engineer
2023 - 2026
Codility
- Owned security-critical identity and access domains for 25+ months across a legacy B2B SaaS platform. Addressed 20+ audit-driven findings across all severity levels, and supported approximately 200+ auth/access endpoints and flows.
- Co-led delivery of an enterprise permissions redesign for a 15+ year-old monolith, shipping an MVP in six months and later becoming a primary owner for bugs, follow-up fixes, and operational continuity after most of the original team rolled off.
- Owned critical-path registration, verification, login, and token lifecycle logic for ARR-impacting payment-linked flows, contributing to a customer-facing initiative with measurable ARR impact over two years and shipping changes in 2 weeks.
- Turned a fragile, high-risk account-merge workflow with ten years of legacy complexity into an enforceable engineering system by adding CI guardrails for schema drift, preventing silent regressions as the data model evolves.
- Built LLM-assisted engineering tooling that connected Jira, observability, code search, and GitLab workflows to speed up debugging and investigation across tickets, logs, and code, helping shape ideas that later evolved into Coherence.
Technologies: Python, Django, React, Next.js, FastAPI, PostgreSQL, Terraform, Authentication, Authorization, AWS IAM, SAML, OAuth, OpenTelemetry, CSS, HTML, Full-stack, Dashboards, API Integration, Web Development, Data Migration, APIs, Automation, System Integration, Full-stack Development, Browser Automation, Back-end, REST APIs, Multi-tenant SaaS, Artificial Intelligence (AI), Distributed Systems, Technical Leadership, Prompt Engineering, Web Security, Performance Optimization, JSON Web Tokens (JWT), OAuth 2, Identity & Access Management (IAM), ABAC, Payment Gateways, Test Automation, Git, Large Language Models (LLMs), AI Agents, Software Architecture, Claude Code, Codex, Cursor AI, REST, GitHub Copilot, Jira, GitLab, SaaS, User Experience (UX), Agentic Coding, Front-end, SQL, Agentic AI, Observability, Performance, Security, Claude, AI-generated Code, AI-assisted Development
Senior Software Engineer
2021 - 2023
Stash
- Achieved significant improvements in user acquisition metrics by improving the web onboarding flow: increased first platform deposit by 11%, decreased referral cost by 32%, and boosted promo redemptions by 35%.
- Improved request traceability, logging, and monitoring across an event-driven architecture consisting of seven or more team-owned microservices, reducing time to identify and resolve issues.
- Built a scalable event aggregation service for Kafka messaging, maintaining a 99.9% SLO for six months.
- Drove team adoption of commit standards, documentation, debt removal, and bug-reporting hygiene to improve velocity and maintainability.
Technologies: CI/CD Pipelines, Datadog, Docker, JavaScript, Kubernetes, Kafka, Kotlin, Node.js, PostgreSQL, React, Redis, Scala, Sentry, Terraform, Amazon Web Services (AWS), CSS, HTML, Full-stack, API Integration, Web Development, APIs, Automation, System Integration, Full-stack Development, Browser Automation, Back-end, REST APIs, Artificial Intelligence (AI), Distributed Systems, CircleCI, Next.js, Web Security, Performance Optimization, JSON Web Tokens (JWT), OAuth 2, Identity & Access Management (IAM), Test Automation, Git, Software Architecture, Ruby on Rails, REST, GitHub Copilot, Jira, Ruby, SaaS, Mobile, User Experience (UX), Front-end, SQL, Observability, Performance, Security, AI-generated Code, AI-assisted Development
Senior Software Engineer
2021 - 2021
Amitree
- Built a custom CI/CD pipeline based on GitLab Auto DevOps and a self-hosted Kubernetes cluster as a proof of concept for migrating from Heroku and reducing hosting costs by 50%.
- Dockerized the application monolith into six services plus job workers.
- Proposed and helped implement a one-step UAT flow with Review Apps, resulting in 20% higher velocity and zero monthly master reverts.
Technologies: Docker, Ember.js, Google API, Heroku, Mailchimp, Mixpanel, PostgreSQL, Redis, Sidekiq, Stripe, Twilio, CSS, HTML, Full-stack, API Integration, Web Development, APIs, Automation, System Integration, Full-stack Development, Back-end, REST APIs, OAuth 2, Payment Gateways, Test Automation, Git, Software Architecture, Ruby on Rails, REST, Jira, GitLab, Ruby, SaaS, SQL
Software Developer
2018 - 2020
True
- Led cross-functional technical delivery for an eCommerce project, guiding three front-end engineers and coordinating with approximately fifteen people across back-end, DevOps, engineering, design, and marketing teams.
- Shaped core architecture for Rails plus Vue/Nuxt, covering Nuxt.js front-end structure, JSON:API serialization, and OAuth 2.0/JWT authentication.
- Resolved performance regressions causing up to 80% slowdown in a mobile-heavy eCommerce storefront by optimizing SQL queries, caching layers, CDN/HTTP/2 delivery, SSR behavior, and JavaScript bundle loading.
- Resolved critical Nuxt.js SSR production incident caused by request-scoped API authentication state being cached in a shared Node.js singleton after JavaScript to TS migration.
- Restored per-user request isolation and shipped a production fix within 20 hours.
Technologies: Nuxt.js, MySQL, Redis, Sidekiq, Docker, Kubernetes, Google Kubernetes Engine (GKE), Google Cloud, Sentry, Rollbar, Ruby, TypeScript, Ruby on Rails 6, CSS, HTML, Full-stack, API Integration, Web Development, Data Migration, APIs, Automation, System Integration, Full-stack Development, Back-end, REST APIs, Distributed Systems, Technical Leadership, CircleCI, Web Security, Performance Optimization, JSON Web Tokens (JWT), JSONAPI::Resources, Identity & Access Management (IAM), Payment Gateways, Test Automation, Git, Software Architecture, Ruby on Rails, REST, eCommerce, Jira, SaaS, Mobile, User Experience (UX), Front-end, SQL, Observability, Performance, Security
Independent Software Developer
2018 - 2018
Self-employed
- Built an open-source eCommerce MVP in three weeks using Rails, Vue.js, Docker, and PayPal payments. Published front-end and back-end repositories on GitHub.
- Transitioned from PHP/Laravel to Ruby/Rails through self-directed full-stack product development.
- Integrated PayPal payments across the Rails API and Vue.js storefront, covering checkout and payment confirmation flows.
Technologies: Ruby, Docker, Vue, PayPal, Payment Gateways, Ruby on Rails 6, CSS, HTML, Full-stack, Dashboards, API Integration, Web Development, APIs, System Integration, Full-stack Development, Back-end, REST APIs, Web Security, JSON Web Tokens (JWT), Open Source, Test Automation, Git, Software Architecture, Ruby on Rails, REST, GitLab, Front-end, SQL, Tailwind CSS
Software Developer
2017 - 2018
Edukey Education
- Developed and launched paid cross-platform safeguarding software used by 350,000+ teachers and four million students in the UK and US, receiving strong end-user feedback.
- Identified inefficient bug tracker usage and introduced practical issue-reporting standards, improving turnaround time for common issues by 15%.
- Reduced development/production environment provisioning time from eight to sixteen hours to approximately fifteen minutes using Vagrant-based automation.
Technologies: CakePHP, Mailgun, MySQL, PHP, Vagrant, Webpack, Vue, CSS, HTML, Full-stack, API Integration, Web Development, APIs, System Integration, Full-stack Development, Back-end, REST APIs, Multi-tenant SaaS, Web Security, mPDF, Test Automation, Git, REST, SaaS, User Experience (UX), Front-end, SQL
Web Developer
2015 - 2017
RXA Technology
- Owed maintenance and UX improvements across several legacy web projects, improving maintainability, performance, and delivery speed.
- Reduced turnaround time for critical bug fixes from approximately eight hours to between one and a half and two hours by adding regression tests around fragile legacy flows.
- Built a secure Stripe-based subscription payment flow for a product used by five hundred or more users, integrating Stripe API/webhooks, structured error logging, and Mailgun alerts.
- Improved engineering quality through code reviews, CI, and TDD practices.
Technologies: MySQL, TypeScript, PHP, CodeIgniter, Laravel, Vue, JavaScript, CSS, HTML, Full-stack, Dashboards, API Integration, Web Development, Data Migration, APIs, Automation, System Integration, Full-stack Development, Back-end, REST APIs, Web Security, JSON Web Tokens (JWT), OAuth 2, Identity & Access Management (IAM), ABAC, Payment Gateways, Test Automation, Git, Software Architecture, REST, Front-end, Security, Tailwind CSS
Web Developer
2015 - 2015
Ahead Technology
- Served as the primary contributor and technical owner for custom Moodle LMS plugins.
- Helped the client launch two months earlier by rapidly prototyping reusable Moodle blocks and modules.
- Improved maintainability and long-term extensibility by documenting custom Moodle plugins and structuring shared functionality as reusable components.
Technologies: PHP, Moodle, YUI, JavaScript, MySQL, CSS, HTML, Full-stack, API Integration, Web Development, APIs, Automation, System Integration, Full-stack Development, Back-end, REST APIs, Web Security, Identity & Access Management (IAM), ABAC, REST, Front-end, SQL
Technical Support Software Engineer
2013 - 2015
Open Technologies
- Led QA release testing and support for a Moodle-based open-source education platform.
- Owned final release checks for new features and translated recurring customer issues into engineering fixes.
- Mentored five junior developers through code reviews, debugging sessions, and production support.
Technologies: PHP, Moodle, JavaScript, YUI, MySQL, CSS, HTML, Full-stack, Dashboards, API Integration, Web Development, Data Migration, APIs, Automation, System Integration, Full-stack Development, Back-end, REST APIs, Multi-tenant SaaS, Web Security, Performance Optimization, JSON Web Tokens (JWT), OAuth 2, Identity & Access Management (IAM), ABAC, Payment Gateways, Open Source, REST, SQL
Experience
Coherence
https://usecoherence.devCoherence is an open-source intent traceability layer for software teams and AI agents. I designed and built its versioned graph model to connect product specifications, acceptance criteria, code changes, and verification evidence.
It makes product intent reviewable, diffable, and testable, so teams can see what changed, why it changed, and whether the implementation still matches the original intent.
It makes product intent reviewable, diffable, and testable, so teams can see what changed, why it changed, and whether the implementation still matches the original intent.
Flexible Roles
Flexible User Roles is Codility’s enterprise permissions system for creating custom roles from granular entitlements and assigning them across internal and externally managed users. I co-led its engineering delivery within a 15+ year-old B2B SaaS monolith, working across authorization logic, domain modeling, APIs, data migration, and administrative workflows. I helped deliver the MVP in approximately six months, then remained a primary owner for production issues and follow-up improvements.
Alongside the permissions redesign, I owned security-critical identity and access domains spanning approximately 200 endpoints and flows. I addressed 20+ audit-driven findings across all severity levels and served as the solo continuity owner for 15+ months after the original team rolled off.
Alongside the permissions redesign, I owned security-critical identity and access domains spanning approximately 200 endpoints and flows. I addressed 20+ audit-driven findings across all severity levels and served as the solo continuity owner for 15+ months after the original team rolled off.
True&Co eCommerce Platform
https://trueandco.comTrue&Co is a direct-to-consumer apparel brand with a mobile-heavy eCommerce storefront. I led cross-functional technical delivery for its custom commerce platform, guiding three front-end engineers and coordinating with approximately 15 people across back-end, DevOps, engineering, design, and marketing teams. I shaped the Rails and Vue/Nuxt architecture, including front-end structure, JSON:API serialization, and OAuth 2.0/JWT authentication.
I resolved performance regressions causing up to an 80% slowdown by optimizing SQL queries, caching, CDN and HTTP/2 delivery, server-side rendering, and JavaScript bundle loading. During a critical production incident, I traced cross-request authentication leakage to shared Node.js state, restored per-user isolation, and shipped the fix within 20 hours.
I resolved performance regressions causing up to an 80% slowdown by optimizing SQL queries, caching, CDN and HTTP/2 delivery, server-side rendering, and JavaScript bundle loading. During a critical production incident, I traced cross-request authentication leakage to shared Node.js state, restored per-user isolation, and shipped the fix within 20 hours.
Stash Web Onboarding
https://www.stash.comStash is a financial technology platform offering investing, advisory, and banking products through a consumer application. I improved its web onboarding and acquisition flows, increasing first platform deposits by 11%, reducing referral costs by 32%, and increasing promotional redemptions by 35%.
Beyond the customer-facing funnel, I improved tracing, logging, and monitoring across an event-driven architecture of seven or more team-owned microservices. I also built a scalable Kafka event aggregation service that maintained a 99.9%+ service-level objective for six months, making production behavior easier to investigate and operate.
Beyond the customer-facing funnel, I improved tracing, logging, and monitoring across an event-driven architecture of seven or more team-owned microservices. I also built a scalable Kafka event aggregation service that maintained a 99.9%+ service-level objective for six months, making production behavior easier to investigate and operate.
Edukey Safeguarding Module
https://www.tes.com/en-gb/for-schools/myconcernEdukey’s safeguarding module was a commercial cross-platform product for recording, reviewing, and reporting student welfare concerns. I developed and launched its reporting interface, translating sensitive safeguarding records into clear, actionable views for school staff. The product was used by more than 350,000 teachers and four million students across the UK and the US and received strong end-user feedback. I also reduced development and production environment provisioning from 8-16 hours to approximately 15 minutes through Vagrant-based automation, making the product easier to develop, test, and support.
Education
2009 - 2013
Bachelor's Degree in Computer Science
Volgograd State University - Volgograd, Russia
Skills
Libraries/APIs
React, Node.js, Vue, REST APIs, Google API, Sidekiq, Stripe, YUI, JSONAPI::Resources, Rollbar, mPDF
Tools
Jira, GitLab, Git, Claude Code, Codex, GitHub Copilot, Terraform, AWS IAM, Sentry, Mailchimp, Google Kubernetes Engine (GKE), Vagrant, Webpack, Moodle, CircleCI, Claude
Languages
JavaScript, TypeScript, Ruby, CSS, HTML, SQL, Python, SAML, Kotlin, Scala, PHP, Rust
Frameworks
Nuxt.js, Ruby on Rails 6, Laravel, OAuth 2, JSON Web Tokens (JWT), Django, Next.js, CakePHP, Tailwind CSS, Ember.js, CodeIgniter
Paradigms
Test Automation, Role-based Access Control (RBAC), ABAC, Automation, REST, Event Sourcing
Platforms
Docker, Kubernetes, Heroku, Mixpanel, Twilio, Mailgun, Amazon Web Services (AWS), Apache Kafka, Mobile
Storage
MySQL, PostgreSQL, Datadog, Redis, Google Cloud, Graph Databases
Other
Authentication, Authorization, CI/CD Pipelines, Ruby on Rails, Software Architecture, Large Language Models (LLMs), Identity & Access Management (IAM), Performance Optimization, Server-side Rendering (SSR), Front-end Development, Web Security, Full-stack, Dashboards, API Integration, Web Development, Data Migration, APIs, System Integration, Full-stack Development, Browser Automation, Back-end, Multi-tenant SaaS, Distributed Systems, Technical Leadership, Cursor AI, eCommerce, SaaS, Agentic Coding, Front-end, Agentic AI, Observability, Performance, Security, AI-generated Code, AI-assisted Development, FastAPI, OAuth, OpenTelemetry, Kafka, Computer Science, AI Agents, Open Source, PayPal, Payment Gateways, Artificial Intelligence (AI), Prompt Engineering, User Experience (UX)
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