# Introduction to API Design Patterns

## What are API Design Patterns?

A **software design *pattern*** is a particular design that can be applied over and over to lots of similar software problems, with only minor adjustments. It is not a pre-built library but more of a *blueprint* for solving similarly structured problems.

- Most often, design patterns focus on specific components rather than entire systems.
    - e.g. If you want to add a logging system, you can use the **singleton design pattern**.
    - This pattern is not complete
    - However, it's well-defined and well-tested pattern to follow when you need to solve this small compartmentalised problem of always having a single instance of a class.

## Why are API Design Patterns Important?

- While having programmatic access to a system is very valuable, it's also much more fragile and brittle.
    - Changes to the interface can easily cause failures for those using the interface.
- We refer to this aspect as *flexibility*
    - Interfaces where users can easily accommodate changes are *flexible*
        - GUIs are flexible - moving a button
    - Interfaces where even small changes cause complete failures are *rigid*.
        - Backend APIs: changing a query parameter breaks old client code.
- Rigid interfaces make it much more difficult to iterate toward a great design.
    - We are often stuck with all design decisions, both good and bad.

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