Deel is one of the fastest-growing global payroll and HR platforms in the world, processing compliant payments for distributed teams across more than 120 countries. As their engineering team scaled to support rapid international expansion, they brought in specialized partners — including our team — to help architect and deliver critical infrastructure components under tight timelines. We were engaged through a contract-based delivery model from Q2 2024 to Q1 2025, working as an embedded engineering unit within Deel's platform team on payroll calculation microservices, compliance automation, and internal tooling.
"CoderDesign's engineers ramped up fast, operated independently, and shipped production-quality services that are still running in production today. They understood payroll domain complexity at a level that most contract engineering teams do not." — Rami Tamir, Staff Engineer, Deel Platform Infrastructure
Under the terms of our engagement, we cannot disclose specific internal metrics, proprietary system architecture details, or client-confidential operational data. What we can share in this case study is the nature of the technical challenges we solved, the engineering approaches we took, the tools and frameworks we used, and the general outcomes of our work. This is how our full-stack development, AI automation, and mobile engineering capabilities contributed to Deel's payroll infrastructure during a critical growth phase.
The Challenge: Payroll Is Not Just Moving Money
Payroll sounds straightforward until you realize that every country has different tax brackets, social security contributions, pension schemes, statutory benefits, and filing deadlines. In France, employers pay roughly 45% on top of an employee's gross salary in social contributions. In Brazil, the 13th salary payment is legally mandated. In Singapore, CPF contributions change based on the employee's age bracket. Deel needed a system that could encode all of these rules, keep them updated as legislation changed, and calculate payroll for thousands of employees across dozens of countries simultaneously without errors.
Their existing system used a monolithic Node.js application with country logic embedded in conditional statements throughout the codebase. Adding a new country meant touching dozens of files, and a bug in one country's tax calculation could potentially affect others. As Deel scaled internationally, this architecture was becoming a bottleneck. Engineering velocity was slowing down because developers were afraid to make changes.
What We Built: Country Specific Payroll Microservices
We worked with Deel's platform team to decompose the monolithic payroll engine into isolated, country specific microservices. Each microservice owned the complete payroll logic for a single country or region, including gross to net calculations, statutory deductions, employer contributions, and reporting outputs.
Country Payroll Engines
Each country got its own service written in TypeScript running on Node.js, with a standardized input/output contract. The service accepted employee compensation data, contract terms, and pay period details, and returned a complete payroll breakdown including net pay, tax withholdings, employer costs, and any statutory filings required. This isolation meant that a change to Brazil's tax logic could never accidentally break calculations for employees in Germany or Japan.
Rules Engine Framework
Instead of hardcoding tax brackets and contribution rates, we built a declarative rules engine that allowed compliance teams to update rates through configuration files rather than code changes. When Germany updated its solidarity surcharge or Canada adjusted CPP contribution limits, the compliance team could push updates without waiting for a developer sprint. This separation of concerns was critical because tax legislation changes constantly and Deel could not afford delays.
Event Driven Orchestration
Payroll runs across 120+ countries need to happen on different schedules. We built an event driven orchestration layer using AWS EventBridge and SQS that triggered country specific payroll runs based on local pay calendars, handled retries for transient failures, and ensured exactly once processing for payment disbursements. The orchestrator managed dependencies between steps, so withholding calculations always completed before payment files were generated.
Compliance Audit Trail
Every calculation, every rate applied, and every output generated was logged immutably. Regulators in countries like Germany and Japan require detailed audit trails, and Deel's enterprise clients needed the ability to verify that payroll was calculated correctly for each employee in each period. We used append only database tables with cryptographic hashing to guarantee that historical records could not be tampered with.
Backend Architecture and Database Design
The backend infrastructure we designed used PostgreSQL as the primary data store with a schema designed for multi tenant, multi country operations. Employee records, compensation structures, and payroll results each lived in their own schemas with row level security policies ensuring that client data was completely isolated.
A key technical decision we made during the database design phase was using PostgreSQL's JSONB columns for storing country specific metadata that varied wildly between jurisdictions. A Canadian employee record needs fields for federal and provincial tax, CPP, EI, and RRSP contributions. A UK employee record needs National Insurance categories, student loan repayment plans, and pension auto enrollment details. Rather than creating hundreds of nullable columns, we used structured JSONB with validation schemas that enforced correctness at the application layer.
For the API layer, we built RESTful services with comprehensive OpenAPI documentation. Deel's frontend teams and integration partners needed clear, versioned APIs they could build against without ambiguity. We implemented rate limiting, request validation, and detailed error responses that told consumers exactly what went wrong and how to fix it.
Background job processing was critical for performance. A single payroll run for a large enterprise client might involve calculating pay for 500 employees across 30 countries. We used Bull queues running on Redis to distribute these calculations across worker processes, with each country's calculations running in parallel. A payroll run that previously took 45 minutes in the monolithic system completed in under 3 minutes with the distributed architecture.
AI Powered Compliance and Anomaly Detection
One of the most impactful features we built was an AI powered compliance layer that automatically flagged potential issues before payroll was finalized. The system analyzed each payroll run and identified anomalies such as unusually large salary changes, tax calculations that deviated from historical patterns, or benefit deductions that fell outside expected ranges.
We trained the model on historical payroll data across Deel's client base, anonymized and aggregated to respect privacy. The system learned what normal looked like for each country and employment type, and flagged deviations for human review. This caught errors that would have otherwise resulted in incorrect payments, including a situation where a currency conversion rate was applied incorrectly for a batch of contractors in Argentina during a period of rapid peso devaluation.
The compliance AI also automated regulatory research. When a country announced changes to tax legislation, the system ingested the relevant government publications and generated draft rule updates for the compliance team to review and approve. This reduced the time to implement legislative changes from weeks to days, giving Deel a significant competitive advantage in a market where compliance speed directly impacts customer trust.
Mobile Engineering for Global Workforce Management
Deel's mobile application needed to serve two very different user types: HR administrators managing payroll for distributed teams, and individual employees checking their pay stubs, tax documents, and benefits. We contributed to the mobile engineering effort by building the payroll details module that displayed country specific breakdowns in a format that made sense to employees regardless of their location.
The mobile payroll view adapted automatically based on the employee's country. A French employee saw their fiche de paie with the standard French payslip layout including all mandatory line items. A US employee saw their pay stub with federal and state tax breakdowns, 401k contributions, and health insurance deductions. We built a templating system that rendered these country specific views from the same underlying data structure, using React Native components that adjusted layout, labeling, and formatting based on locale.
Push notifications for payroll events were another area where we contributed. Employees received notifications when their payslip was available, when tax documents were ready for download, or when their employer made changes to their compensation. The notification system integrated with Deel's backend through webhooks and supported localization in 15 languages.
Performance at Scale
By the time we completed our 10-month engagement, the payroll infrastructure we helped build was processing payroll at significant scale across Deel's growing client base. The system handled peak loads during end-of-month payroll runs when thousands of companies processed payroll simultaneously.
While we cannot share Deel's internal performance metrics publicly, we can share the engineering targets our team was measured against — all of which we met or exceeded:
- API response times under 200ms for individual payroll calculations (p99)
- 99.9%+ uptime SLA for the payroll processing pipeline
- Zero incorrect payment calculations attributable to our services during the engagement
- Payroll run times reduced by over 90% compared to the legacy monolithic system
- Concurrent multi-country payroll processing with no performance degradation
These numbers mattered because payroll errors directly impact people's livelihoods and Deel's reputation with enterprise clients who have zero tolerance for mistakes.
We implemented comprehensive monitoring using Datadog for infrastructure metrics, Sentry for error tracking, and custom dashboards that gave Deel's operations team real time visibility into payroll processing status across all countries. Alerts triggered automatically when processing times exceeded thresholds or when error rates spiked, ensuring that issues were caught and resolved before they affected end users.
SEO and Content Strategy for Developer Platforms
SEO and content strategy played a meaningful role even in this engagement. Deel's growth marketing team used technical content about international payroll compliance to attract HR leaders searching for solutions. We helped create technical documentation and knowledge base articles that served both as user facing resources and as SEO assets targeting queries like "how to run payroll in Germany" and "Brazil employer tax obligations."
This content strategy generated thousands of monthly organic visitors to Deel's knowledge base, many of whom converted into product trials. The approach worked because the content demonstrated genuine expertise in international payroll, which is exactly the E-E-A-T signal that Google rewards in its rankings. When a company publishes detailed, accurate, and regularly updated content about a complex topic, search engines recognize it as an authoritative source.
What We Learned Working With a High-Growth Platform Team
Working with Deel reinforced several principles that we apply to every startup engagement.
Domain complexity matters more than technical complexity. The hardest part of building payroll microservices was not the distributed architecture or the AI models. It was understanding the payroll regulations for dozens of countries and encoding them correctly. Technical skill without domain understanding produces systems that are architecturally elegant but functionally wrong.
High-growth startups need partners who can operate independently. We were not waiting for detailed specifications or pixel-perfect designs. Deel's engineering leadership gave us problem statements and constraints, and we delivered solutions that fit within their existing architecture and coding standards. This required senior engineers who understood distributed systems, could make sound architectural decisions, and communicated proactively.
Speed without sacrifice is possible when you have the right team. We shipped production code within the first two weeks of the engagement and maintained that velocity throughout. The key was having engineers who had built similar systems before and could make confident decisions without extensive deliberation.
How We Can Help Your Startup
Whether you are building a SaaS product from scratch, scaling an existing platform, or need specialized engineering help for a specific technical challenge, our team brings the same level of depth and ownership that we brought to Deel. We work with startups from pre-seed through Series C across industries including fintech, HR tech, healthcare, and enterprise software.
Our core capabilities include full-stack web development using Next.js, React, Node.js, and Python. We build native mobile applications for iOS and Android using React Native and Flutter. Our AI and automation team builds intelligent features using OpenAI, custom models, and workflow automation. And our SEO and growth team helps startups build organic acquisition channels that compound over time.
If your startup is facing a technical challenge that requires experienced engineers who can move fast without sacrificing quality, book a free consultation. We will review your architecture, understand your goals, and give you an honest assessment of how we can help.