Interface Designer

Design an Interface

Philosophy

Every interface design involves tradeoffs you cannot see from a single perspective. Designing it twice (or three times) with radically different constraints forces you to explore the design space before committing. This skill spawns parallel sub-agents, each constrained differently, then compares and synthesizes.

Workflow: 5 Phases

Phase 1: Gather Requirements

Before spawning any sub-agents, clarify:

• What problem does this interface solve?
• Who are the callers? What do they need?
• What are the invariants the interface must preserve?
• What are the performance / ergonomic / safety constraints?

Do NOT start designing until requirements are agreed upon.

Phase 2: Spawn Divergent Sub-Agents

Launch 3+ parallel sub-agents (via Agent tool with subagent_type), each given the same requirements but a different constraint set. Constraints must force radically different designs -- not minor variations. See [constraints.md](constraints.md) for examples.

Each sub-agent produces:

• Interface definition (function signatures, types, module API)
• Usage example for the most common case
• One paragraph on the tradeoff it optimized for

Phase 3: Present Designs

Show all designs side-by-side. Label each by its primary constraint. Do not editorialize yet -- let the user see the raw options.

Phase 4: Comparative Evaluation

Evaluate every design against Ousterhout's criteria. See [evaluation-criteria.md](evaluation-criteria.md) for the full rubric. Score each design on:

• Depth (small interface, rich implementation)
• Simplicity of the common case
• Resistance to misuse
• General-purpose vs specialized tradeoff
• Implementation efficiency

Phase 5: Synthesize

Combine the best elements into a final design. Explain which parts came from which design and why. The synthesis is often none of the originals -- it is a new design informed by all of them.

Rules

• Never present fewer than 3 designs.
• Designs must be structurally different, not cosmetic variations.
• Evaluate on caller ergonomics, not implementation convenience.
• Prefer deep modules: small interface surface, rich behavior behind it.
• If all designs converge, your constraints were too similar -- re-run with harder constraints.

What You Get

• Three or more structurally distinct interface designs, each optimized for a different constraint set.
• A side-by-side comparative evaluation scored against Ousterhout's criteria (depth, simplicity, misuse resistance).
• A synthesized final design that combines the strongest elements from all candidates, with rationale for each choice.

Sub-files

| File | Topic | |------|-------| | [evaluation-criteria.md](evaluation-criteria.md) | Ousterhout evaluation rubric | | [constraints.md](constraints.md) | Divergent constraint sets for sub-agents |

Source & license

This open-source skill is cataloged on AgentStack and links to its original source — we do not rehost the code.

• Author: DROOdotFOO
• Source: DROOdotFOO/agent-skills
• License: MIT
• Homepage: https://droo.foo/

Install and usage instructions live in the source repository linked above.