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When a product incorporates an API, or when the API itself is the product, it's crucial to take a page out of the UX playbook. It's not enough to just 'open' your API – considering its usability is key.
While the core service behind remains the most important part of the offer, the usability of the API could impact adoption, influence technical recommendations in the purchase process, and it's important to consider a few points not always associated with API requirements:
User (Developer) Experience (UX)
Software developers, the user of APIs, are engineers by day, not perpetual hackers. They need APIs that are straightforward and efficient, not puzzles to solve. An API must be intuitive, with self-explanatory signifiers.
Your API shouldn't reflect internal complexities. Like any product, it should focus on solving customer problems. Complexity isn't a feature; it's a bug.
API Usability Testing
Validation should mirror consumer validation processes, namely through user testing.
Independent validation is key. Test your API with external developers unfamiliar with your domain before release.
Key Performance Indicators (KPIs) of usability testing: Time to solve a problem, lines of code required, the mistakes count developers make, and even the frequency of documentation usage.
In the era of LLM you can even validate if LMM is generating correct code when grounded with your documentation.
Consistency
Internal: Ensure internal logical consistency: Avoid multiple paths for the same outcome, standardize naming conventions, and ensure uniform data structures.
Company: Ensure consistency across your company's API portfolio. It shapes perceptions of your company and influences confidence in long-term support.
Global: Align with global standards and market leaders. Don’t reinvent the wheel. Emulate popular APIs to facilitate a smoother learning curve.
Graceful Error Handling
Errare humanum est, and your API should provide clear feedback on errors, such as missing parameters or data issues - make user's mistakes your team's problem. Remember, a frustrated developer can be the greatest enemy of your success.
Documentation
Documentation should be short, easy to search (single page if possible) and inclusive of ready-to-use examples or a sandbox environment.
Versioning
It’s likely your R&D manager is on top of this, but ensure your team adheres to semantic versioning. There’s no need to reinvent the wheel here.
Performance and Scalability
Although primarily a service behind API concern, ensure that performance requirements are reassessed when exposing your service through an API. Be prepared for varying scale and latency demands across different markets and use cases.
Rate limits & usage caps could be a necessary evil - automatic scalability is better (unless your service is free/mium).
Latency and instability are UX killers for upstream applications.