Harish Kumar — freelance web application developer Hire me

Freelance • Remote • India & Europe

Freelance Web Application Developer for Businesses in India & Europe

I’m Harish Kumar, a freelance web application developer and backend architect with 15+ years of experience. I design, build and rescue scalable web apps, APIs, cloud infrastructure and AI-driven systems for eCommerce, finance, accounting and SaaS companies — working remotely across IST and CET hours.

Hire a freelance web app developer See project results
Experience
15+ years
Domains
Ecommerce • Finance • Accounting
Stack
Java • Go • PHP • Python • C# • NestJS
Cloud & Infra
AWS • Docker • K8s • CI/CD

About Harish Kumar — freelance web application developer

For over 15 years I have built web applications that have to keep working: order systems that spike on campaign days, accounting platforms that must reconcile to the cent, and internal tools that quietly run a business. I work as an independent contractor, which means you get the person who designs the architecture, writes the code and stays accountable for it in production — not a rotating team.

On the backend I work with Java (Spring, Spring Boot, Play), Python (Django, FastAPI), PHP (Laravel), Node.js (NestJS), Go and C#/.NET, backed by MySQL, SQL Server, PostgreSQL and MongoDB, with Redis and Elasticsearch for caching and search.

I also design and deploy LLM-powered features using ChatGPT, Claude, Gemini, DeepSeek and Grok — fine-tuning, prompt engineering, RAG systems and AI copilots wired into real enterprise workflows. Delivered work spans CMS, CRM, ERP, accounting and eCommerce platforms, with integrations into QuickBooks, Xero, Sage, Salesforce, Zendesk, Shopify and WooCommerce.

Freelance web application development services

Hire me for a single audit, a defined project, or as an embedded senior engineer inside your team.

Custom web application development

Business portals, dashboards, marketplaces and SaaS products built end to end — from data model and authentication to billing, roles and reporting.

Backend architecture & API development

Scalable microservices, REST and GraphQL APIs, versioning strategies, secure contracts, API gateways and event-driven messaging with Kafka or RabbitMQ.

AI engineering & RAG integration

LLM integration, retrieval-augmented generation, domain fine-tuning and AI assistants embedded into support, sales and accounting workflows.

Cloud native & DevOps

CI/CD pipelines, Docker, Kubernetes, observability and monitoring, cloud cost optimisation and secure deployments on AWS and Azure.

Database design & performance tuning

Schema design, indexing, partitioning, query rewrites, caching strategy and OLAP/OLTP balancing for slow, growing databases.

Legacy modernisation & migration

Monolith-to-microservices refactoring, framework and runtime upgrades, data migrations and zero-downtime cutovers for systems you cannot switch off.

Integrations & automation

Payment gateways, ERP and accounting integrations (QuickBooks, Xero, Sage), SaaS connectors and automation scripts in Python and PHP.

Code audits, security & maintenance

Architecture and code audits, performance investigations, security reviews, dependency upgrades and test-coverage recovery.

Embedded senior engineer / CTO support

Part-time technical leadership for funded startups: design reviews, hiring support, roadmap sanity checks and hands-on delivery alongside your team.

Technology stack for web application projects

Working with clients in India and Europe

Same engineer, two working cultures — invoicing, contracts and working hours adapted to where you are.

Freelance web app developer in India

I work with Indian startups, D2C brands, SaaS companies and agencies in Bengaluru, Delhi NCR, Mumbai, Hyderabad, Pune and Chennai — remotely, with on-site visits possible for kickoff or critical releases.

  • • IST working hours and same-day responses
  • • GST-compliant invoicing in INR
  • • Experience with UPI, Razorpay, PayU and GST-compliant accounting flows
  • • White-label delivery for agencies and consultancies

Freelance web app developer for Europe

I contract with companies across Germany, the Netherlands, the UK, Switzerland, Ireland, France, Spain, Belgium, Poland and the Nordics — as an independent contractor under your own MSA, NDA and IP-assignment terms.

  • • 5–6 hours of daily overlap with CET/CEST business hours
  • • GDPR-aware architecture: data minimisation, EU-region hosting, audit logs, deletion and export flows
  • • Invoicing in EUR or GBP via bank transfer or Wise
  • • Integrations with SEPA, Stripe, Adyen, Mollie, Xero and Sage

Industries I build for

eCommerce & retail

Catalogue, checkout, pricing engines, order management and Shopify / WooCommerce integrations built to survive traffic spikes.

Finance & fintech

Reconciliation, ledgers, reporting engines, payment gateway integrations and audit-ready data trails.

Accounting & ERP

QuickBooks, Xero, Sage and MyOB integrations, invoicing automation and tax-compliant reporting.

SaaS & B2B platforms

Multi-tenant architecture, subscription billing, role-based access, usage metering and admin tooling.

Selected web application projects & measurable impact

Client names are withheld under NDA; the problems, stacks and outcomes are described as delivered.

Enterprise eCommerce platform re-architecture

Broke a slow monolith into services with clear ownership boundaries, added caching and async order processing — 3× throughput and 60% lower checkout latency.

Java • Spring Boot • Kafka • Redis • Kubernetes

Financial reporting & reconciliation engine

Built a reconciliation and reporting engine integrated with QuickBooks and Xero, automating 80% of manual ledger work and closing the monthly books in hours instead of days.

Java • PostgreSQL • QuickBooks & Xero APIs

AI copilot for customer support

Implemented a RAG-based assistant over the client’s help centre and ticket history, cutting first response times and deflecting repetitive support tickets away from the team.

Python • Vector search • LLM APIs • Zendesk

Accounting automation for SMBs

Developed integrations with Sage and MyOB that automated invoicing and produced GST-compliant reports, removing a recurring monthly bottleneck for finance staff.

PHP • Laravel • Sage & MyOB APIs

How to hire me: engagement models

Fixed-scope project

A defined outcome, agreed milestones and a fixed price. Best when the requirements are clear and you want budget certainty.

Monthly retainer

A reserved number of days per month for ongoing development, maintenance and architecture ownership. Best for products in active growth.

Audit or short sprint

One to two weeks to diagnose performance, security or architecture problems and hand back a prioritised plan you can act on with or without me.

  1. 1. Brief
    You send goals, timeline and constraints.
  2. 2. Proposal
    You get an architecture sketch, estimate and plan.
  3. 3. Build
    Weekly demos, code in your repo, CI from day one.
  4. 4. Handover
    Docs, runbooks and full IP transfer on payment.

Frequently asked questions

Do you work with clients based in Europe from India?

Yes. I work remotely with European clients every week and keep my afternoon and evening hours aligned to CET/CEST, which gives a 5–6 hour daily overlap with teams in Germany, the Netherlands, the UK, the Nordics and the rest of the EU. Stand-ups, reviews and releases happen inside your working day, not after it.

What does a freelance web application developer cost?

Engagements are priced either hourly, as a monthly part-time retainer, or as a fixed-scope project with milestone payments. Rates depend on the stack, the level of architecture ownership and the length of the engagement. Send a short brief and you get an estimate with a suggested architecture and timeline, usually within two working days.

Which technologies do you build web applications with?

Java with Spring Boot, Python with Django and FastAPI, PHP with Laravel, Node.js with NestJS, Go, and C#/.NET on the backend; PostgreSQL, MySQL, SQL Server and MongoDB for data; Redis and Elasticsearch for caching and search; Docker, Kubernetes, AWS and Azure for delivery.

Can you take over an existing codebase instead of starting from scratch?

Yes. A large share of my work is inherited code: legacy monoliths, unmaintained plugins, slow queries and half-finished migrations. Typical entry points are a code and architecture audit, a performance investigation, or a migration plan with a zero-downtime cutover.

How do you handle GDPR and data protection for EU clients?

I work under your DPA and sub-processor terms, keep personal data inside EU regions when your architecture requires it, and design for data minimisation, encryption at rest and in transit, audit logging, and deletion and export flows for data-subject requests.

How do contracts and invoicing work?

I sign your MSA, NDA and IP-assignment paperwork, or supply a simple contract if you prefer. European clients are invoiced in EUR or GBP by bank transfer or Wise; Indian clients are invoiced in INR with GST details. All source code and IP transfer to you on payment.

How quickly can you start a new project?

Small audits and fixed-scope pieces can usually start within a week. Longer engagements and full-time retainers typically start within two to four weeks depending on current commitments.

Do you also add AI features to existing web applications?

Yes. Common requests are retrieval-augmented search over company documents, AI copilots inside admin panels, ticket deflection for support teams, and document extraction for accounting and invoicing workflows, built on ChatGPT, Claude, Gemini or self-hosted models.

Hire a freelance web application developer

Share a brief of your project and timeline — you’ll get back a suggested architecture, a rough estimate and clear next steps. Clients in India and Europe are equally welcome.

Or email me directly at honeyonsys@gmail.com — replies within one working day.