structure-behavior-design-interface-design

id	structure-behavior-design.skill.interface-design
kind	skill
name	structure-behavior-design-interface-design
description	Internal Structure-Behavior Design skill for interface, signature, and contract design. Use only as part of the Structure-Behavior Design workflow.
tags	["structure-behavior-design","internal"]
tools	{"claude":{"enabled":true,"frontmatter":{"user-invocable":false}}}

Interface Design

Goal

Design clear boundaries and contracts before implementation.

Design principles

Interfaces should be:

• small
• consumer-oriented
• explicit
• testable
• based on problem-area vocabulary
• independent from infrastructure details

Design before implementation

For each interface, function, or method, define:

• purpose
• consumer
• inputs
• outputs
• error contract
• side effects
• example call site
• implementation detail that must remain hidden

Avoid

• vague names such as Process, Execute, Handle when a domain-specific name exists
• too many primitive parameters
• boolean flags that switch behavior
• infrastructure DTOs leaking into core interfaces
• large interfaces built around providers instead of consumers
• test-only abstractions with no real boundary

Required output

Proposed Interfaces / Signatures

Name	Consumer	Responsibility	Signature	Error Contract

Example Call Sites

// show intended usage here

Boundary Decisions

Boundary	Hidden detail	Reason

Interface Risks

• Oversized interfaces:
• Primitive obsession:
• Infrastructure leakage:
• Boolean flag risks: