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How HMRC built a world-leading API platform to drive digital change at scale
To meet the rising demand for digital tax services, HMRC needed a secure and scalable way to connect third-party developers and government users with its services. By partnering with Equal Experts to build a robust API Platform, HMRC now supports over 140 APIs, 2,600+ live applications, and billions of secure digital transactions annually, driving transformation across government and industry.
In a fast-changing digital landscape, HMRC recognised the need to shift from siloed systems to open, developer-friendly APIs that enable interoperability, efficiency, and faster change. Equal Experts partnered with HMRC to deliver an API Platform that would become foundational to digital government—reducing time-to-market, enabling international integration, and unlocking new digital services across the UK’s tax ecosystem. The result is a modern, secure, and developer-focused platform that powers mission-critical services, improves agility, and has been adopted as a model by other governments worldwide.
About HMRC
HMRC is a non-ministerial department of government. It is the UK’s tax, payments and customs authority, and has a vital purpose: gathering the approximately £740bn tax revenue that pays for the UK’s public services (e.g. hospitals, schools, infrastructure), and helping families and individuals with targeted financial support.
Industry
Government
Organisation size
66k+
Location
Government hubs across the UK
Challenge
Building a future-ready tax ecosystem through APIs
By the mid-2010s, HMRC was facing growing pressure to modernise its digital interfaces and better serve an increasingly digital-first society. Internally, HMRC had a growing number of integration services, but lacked a scalable, secure way to expose these to external software providers, businesses, and other government departments.
Externally, the tax technology landscape was changing fast. Businesses and citizens were turning to commercial tax software to streamline their tax submissions and reporting. HMRC needed to meet this demand while ensuring robust control, security, and agility.
The publication of HMRC’s Third Party Tax Software and API Strategy laid out a bold vision: to build a well-governed, secure, and developer-friendly API ecosystem that would support the Making Tax Digital (MTD) programme and enable a more flexible, modular approach to tax system integration.
Key drivers behind this strategy included:
- Replacing legacy interfaces, such as the aging Government Gateway, with modern APIs that supported real-time interactions and finer-grained access control.
- Stimulating a vibrant commercial software market, giving businesses and individuals more choice through third-party applications.
- Improving delivery agility, by adopting reusable, modular API services that could evolve quickly and reduce duplication.
- Strengthening security and auditability, by embedding OAuth-based access management and standardised approval processes.
- Enabling cross-government interoperability, aligning with wider GDS objectives for reusable public sector platforms.
HMRC needed an approach that could scale quickly, support rapid policy change, and provide developers—both internal and external—with the tools they needed to integrate securely and confidently. Without a shift to an API-first model, the organisation risked being unable to keep pace with growing digital demand, rising user expectations, and a rapidly evolving policy landscape.
Approach
Building a developer-centric, scalable API platform
Working with Equal Experts, HMRC designed and delivered a secure API Platform built on modern cloud infrastructure (AWS), layered on top of HMRC’s Multi-Channel Digital Tax Platform (MDTP).
Key components included:
- Developer hub – A self-service portal providing API documentation, sandbox testing, and subscription tools.
- OAuth-based access control – Secure authentication and fine-grained access management.
- Gatekeeper – Internal tools to manage and support third-party developers.
- API catalog – A searchable registry of available APIs with different access levels (public, private, restricted).
- Federated model – Standards, tooling, and support to allow decentralised API development across HMRC.
- Terms of use & support processes – Clear governance balanced with low friction for adoption.
This platform enabled HMRC to scale from a few APIs to a production-grade ecosystem powering internal systems, external integrations, and third-party services.
Key Decisions
What made the platform a success
Several strategic decisions were crucial to the platform’s success:
- Federated model over centralised control
Instead of building every API, the API Platform team chose to empower teams across the organisation by providing standards, guidance, and tooling. This created a scalable, decentralised delivery model.
- Developer experience first
The team focused on making it easy for developers to access, test, and adopt APIs—driving adoption and innovation. Sandbox environments, clear documentation, and self-service tools made onboarding seamless.
- Industry standards and open source
By adopting OAuth for security and industry-standard API specifications, HMRC improved interoperability and trust.
- Governance that enables innovation
Light-touch Terms of Use and a frictionless production application process encouraged early experimentation while maintaining robust audit and access controls. Our governance and development process also ensured standards compliance (GDPR, accessibility and security).
- Continuous delivery and zero downtime
The platform supports daily releases with no downtime, ensuring rapid iteration and high service availability.
- High availability infrastructure
Moving to AWS enhanced the platform’s scalability and resilience, enabling seamless support for high transaction volumes.
Results
A Platform with national and international impact
The API Platform has become a pillar of HMRC’s digital estate and a benchmark for public sector innovation:
- 142 Production APIs in use across government, commercial partners, and international systems.
- 2,600+ Live Applications consuming these APIs in production.
- 5,800+ Sandbox Applications used by developers to test and integrate services.
- 28,000+ Registered Developers exploring and building services.
- Billions of Transactions annually—growing year-on-year and powering critical national infrastructure.
- 410+ Days of Continuous Uptime, demonstrating exceptional platform stability.
- Daily Production Releases with no service disruption.
Broader business impact
- Accelerated Digital Change: Dramatic reductions in delivery lead times.
- Increased Adoption: Significant ecosystem growth across tax software providers (e.g., Sage, Intuit).
- Cross-Government Influence: The platform model has been studied and emulated by the NHS, Danish and Australian and Canadian tax authorities
- Strategic Enabler: Supports HMRC’s internal platform strategy, product-based transformation, and international treaty requirements for data exchange.
The HMRC API Platform didn’t just meet its original objectives—it exceeded them, becoming a key part of the UK’s digital government infrastructure and a leading example of what a focused, federated, and developer-first approach can achieve.