Catalog
concept#Architecture#Software Engineering#Integration#Security

API Design

Principles and guidelines for designing interfaces that ensure interaction, stability, and evolvability between systems.

API design defines principles and decisions for shaping interfaces that enable communication, stability, and evolution of systems.
Established
Medium

Classification

  • Medium
  • Technical
  • Architectural
  • Intermediate

Technical context

API gateway (e.g., Kong, AWS API Gateway)Service mesh and observability toolsClient generators and SDK tooling

Principles & goals

Clear, well-documented contract (Contract First).Explicit versioning rules and backward compatibility.Security and resilience as integral parts.
Build
Domain, Team

Use cases & scenarios

Compromises

  • Breaking changes can cause outages for external consumers.
  • Insufficient authentication can lead to security incidents.
  • Poor documentation increases support effort and error rates.
  • Contract-first approach using OpenAPI specifications.
  • Clear versioning strategy and deprecation policy.
  • Standardized error codes and comprehensive examples in documentation.

I/O & resources

  • Business and functional requirements
  • Data model and domain semantics
  • Security and compliance requirements
  • API specification (e.g., OpenAPI)
  • Test cases and contract tests
  • Operational and monitoring definitions

Description

API design defines principles and decisions for shaping interfaces that enable communication, stability, and evolution of systems. It covers contract design, versioning, authentication, error handling, and consistency rules. Good API design reduces integration effort, improves maintainability, and supports scalable, secure architectures while clarifying team responsibilities.

✔

  • Reduced integration effort between teams and systems.
  • Improved maintainability and clearer responsibilities.
  • Scalability through consistent contracts and instrumentation.

✖

  • Requires discipline in specification maintenance and governance.
  • Complexity with heterogeneous clients and legacy systems.
  • May incur initial overhead for design reviews.

  • Error rate

    Proportion of erroneous API responses relative to total calls.

  • Latency (P95)

    95th percentile of response times as performance indicator.

  • Adoption rate of API versions

    Share of clients migrated to a new API version.

OpenAPI-based contract definition

Using an OpenAPI specification for automated documentation and client generation.

Versioning via path segment

Introducing v1/v2 in the path to ensure compatibility and enable migrations.

Hypermedia hints for evolvable APIs

Using HATEOAS-like links to reduce rigid contracts and support evolution.

1

Gather requirements and set goals.

2

Design and validate specification (Contract First).

3

Integrate automated tests and CI pipeline.

4

Introduce documentation, monitoring, and versioning process.

⚠️ Technical debt & bottlenecks

  • Inconsistent endpoint naming conventions across services.
  • Incomplete or outdated API documentation.
  • Missing automation of contract tests.
VersioningCompatibilityAuth and rate limits
  • Changing field names without versioning that breaks clients.
  • Exposing sensitive data in API responses without filtering.
  • Omitting error codes and clear status messages.
  • Premature optimization of formats instead of API usability.
  • Ignoring client feedback during design iterations.
  • Missing backward compatibility strategy when changing APIs.
API design and specification knowledge (OpenAPI)Security and authentication knowledgeExperience with distributed systems and fault tolerance
Interoperability with external systemsScalability and performanceSecurity and access control
  • • Existing legacy clients dictate compatibility requirements.
  • • Regulatory requirements for data security and privacy.
  • • Constraints from API gateway or infrastructure features.