Agent skill

Design An Interface

Generates and compares parallel interface designs (Ousterhout 'Design It Twice').

Apache-2.0Auto-check: notesBackend & APIs

Install Design An Interface

skills CLI

$ npx skills add softspark/ai-toolkit --skill design-an-interface -a claude-code

Project install by default; add -g for ~/.claude/skills/.

GitHub CLI

$ gh skill install softspark/ai-toolkit design-an-interface --agent claude-code

Project scope by default; add --scope user for a personal install. Needs GitHub CLI 2.90.0 or later (public preview).

Manual copy

$ git clone --depth 1 https://github.com/softspark/ai-toolkit.git skills-src && mkdir -p .claude/skills && cp -r skills-src/app/skills/design-an-interface .claude/skills/design-an-interface && rm -rf skills-src

Use ~/.claude/skills/ instead of .claude/skills for a personal install. The folder must contain SKILL.md.

Claude Code skills documentation · loads skills from .claude/skills/

Paste into Claude Code

Install the "design-an-interface" agent skill from https://github.com/softspark/ai-toolkit/tree/main/app/skills/design-an-interface into .claude/skills/design-an-interface/ in this project. Copy the whole folder (SKILL.md and every file beside it), keep the folder name "design-an-interface", then confirm the skill loads.

Claude Code copies the folder itself, the same result as the manual copy. Check what it changed before you commit it.

$skill-installer

$skill-installer install https://github.com/softspark/ai-toolkit/tree/main/app/skills/design-an-interface

Type this inside Codex. $skill-installer <name> installs a curated skill from openai/skills. The installer writes to $CODEX_HOME/skills (default ~/.codex/skills). Restart Codex if the skill does not show up.

skills CLI

$ npx skills add softspark/ai-toolkit --skill design-an-interface -a codex

Project install goes to .agents/skills/; add -g for ~/.codex/skills/.

GitHub CLI

$ gh skill install softspark/ai-toolkit design-an-interface --agent codex

Project scope by default (.agents/skills/); add --scope user for a personal install.

Manual copy

$ git clone --depth 1 https://github.com/softspark/ai-toolkit.git skills-src && mkdir -p .agents/skills && cp -r skills-src/app/skills/design-an-interface .agents/skills/design-an-interface && rm -rf skills-src

Use ~/.agents/skills/ instead of .agents/skills for a personal install.

Codex skills documentation · loads skills from .agents/skills/

Paste into Codex

Install the "design-an-interface" agent skill from https://github.com/softspark/ai-toolkit/tree/main/app/skills/design-an-interface into .agents/skills/design-an-interface/ in this project. Copy the whole folder (SKILL.md and every file beside it), keep the folder name "design-an-interface", then confirm the skill loads.

Codex copies the folder itself, the same result as the manual copy. Check what it changed before you commit it.

skills CLI

$ npx skills add softspark/ai-toolkit --skill design-an-interface -a cursor

Project install goes to .agents/skills/; add -g for ~/.cursor/skills/.

GitHub CLI

$ gh skill install softspark/ai-toolkit design-an-interface --agent cursor

Project scope by default (.agents/skills/); add --scope user for a personal install.

Manual copy

$ git clone --depth 1 https://github.com/softspark/ai-toolkit.git skills-src && mkdir -p .cursor/skills && cp -r skills-src/app/skills/design-an-interface .cursor/skills/design-an-interface && rm -rf skills-src

Use ~/.cursor/skills/ instead of .cursor/skills for a personal install.

Cursor skills documentation · loads skills from .cursor/skills/, .agents/skills/, .claude/skills/, .codex/skills/

Paste into Cursor

Install the "design-an-interface" agent skill from https://github.com/softspark/ai-toolkit/tree/main/app/skills/design-an-interface into .cursor/skills/design-an-interface/ in this project. Copy the whole folder (SKILL.md and every file beside it), keep the folder name "design-an-interface", then confirm the skill loads.

Cursor copies the folder itself, the same result as the manual copy. Check what it changed before you commit it.

gemini skills install

$ gemini skills install https://github.com/softspark/ai-toolkit.git --path app/skills/design-an-interface

--scope user (default) or --scope workspace; --path is the subfolder of the repo that holds the skill; --consent skips the security confirmation prompt.

skills CLI

$ npx skills add softspark/ai-toolkit --skill design-an-interface -a gemini-cli

Project install goes to .agents/skills/; add -g for ~/.gemini/skills/.

GitHub CLI

$ gh skill install softspark/ai-toolkit design-an-interface --agent gemini-cli

Project scope by default (.agents/skills/); add --scope user for a personal install.

Manual copy

$ git clone --depth 1 https://github.com/softspark/ai-toolkit.git skills-src && mkdir -p .gemini/skills && cp -r skills-src/app/skills/design-an-interface .gemini/skills/design-an-interface && rm -rf skills-src

Use ~/.gemini/skills/ instead of .gemini/skills for a personal install, then run /skills reload.

Gemini CLI skills documentation · loads skills from .gemini/skills/, .agents/skills/

Paste into Gemini CLI

Install the "design-an-interface" agent skill from https://github.com/softspark/ai-toolkit/tree/main/app/skills/design-an-interface into .gemini/skills/design-an-interface/ in this project. Copy the whole folder (SKILL.md and every file beside it), keep the folder name "design-an-interface", then confirm the skill loads.

Gemini CLI copies the folder itself, the same result as the manual copy. Check what it changed before you commit it.

GitHub CLI

$ gh skill install softspark/ai-toolkit design-an-interface

Installs for Copilot at project scope by default; add --scope user for a personal install. Preview a skill first with gh skill preview. Needs GitHub CLI 2.90.0 or later (public preview).

skills CLI

$ npx skills add softspark/ai-toolkit --skill design-an-interface -a github-copilot

Project install goes to .agents/skills/; add -g for ~/.copilot/skills/.

Manual copy

$ git clone --depth 1 https://github.com/softspark/ai-toolkit.git skills-src && mkdir -p .github/skills && cp -r skills-src/app/skills/design-an-interface .github/skills/design-an-interface && rm -rf skills-src

Use ~/.copilot/skills/ instead of .github/skills for a personal install. Commit .github/skills so cloud agent and code review can use it.

GitHub Copilot skills documentation · loads skills from .github/skills/, .claude/skills/, .agents/skills/

Paste into GitHub Copilot

Install the "design-an-interface" agent skill from https://github.com/softspark/ai-toolkit/tree/main/app/skills/design-an-interface into .github/skills/design-an-interface/ in this project. Copy the whole folder (SKILL.md and every file beside it), keep the folder name "design-an-interface", then confirm the skill loads.

GitHub Copilot copies the folder itself, the same result as the manual copy. Check what it changed before you commit it.

skills CLI

$ npx skills add softspark/ai-toolkit --skill design-an-interface -a opencode

OpenCode documents no install command of its own. Project install goes to .agents/skills/; add -g for ~/.config/opencode/skills/.

GitHub CLI

$ gh skill install softspark/ai-toolkit design-an-interface --agent opencode

Project scope by default (.agents/skills/); add --scope user for a personal install.

Manual copy

$ git clone --depth 1 https://github.com/softspark/ai-toolkit.git skills-src && mkdir -p .opencode/skills && cp -r skills-src/app/skills/design-an-interface .opencode/skills/design-an-interface && rm -rf skills-src

Use ~/.config/opencode/skills/ instead of .opencode/skills for a personal install.

OpenCode skills documentation · loads skills from .opencode/skills/, .claude/skills/, .agents/skills/

Paste into OpenCode

Install the "design-an-interface" agent skill from https://github.com/softspark/ai-toolkit/tree/main/app/skills/design-an-interface into .opencode/skills/design-an-interface/ in this project. Copy the whole folder (SKILL.md and every file beside it), keep the folder name "design-an-interface", then confirm the skill loads.

OpenCode copies the folder itself, the same result as the manual copy. Check what it changed before you commit it.

Facts

Skill name: design-an-interface
GitHub stars: 179
Token cost: ~952 tokens
SKILL.md length: 433 words
Files: 1
Skills in repo: 112
Repo updated: Oct 7, 2026
First seen: Oct 7, 2026
Licence: Apache-2.0

At a glance

Generates and compares parallel interface designs (Ousterhout 'Design It Twice').

Works in 5 steps: Gather Requirements → Generate Designs (Parallel Sub-Agents) → Present Designs → …
Tasks that involve API design
SKILL.md covers Usage, What This Command Does, Process and Visual Companion (Optional), plus 2 more sections
Instructions only: no scripts, shell commands, URLs or credentials in SKILL.md

What it does

Design An Interface is an agent skill from softspark/ai-toolkit. Generates and compares parallel interface designs (Ousterhout 'Design It Twice'). Triggers: design API, interface options, compare modules, design it twice.

Its SKILL.md is about 950 tokens, which your agent loads only when the skill is triggered. It is a single SKILL.md file with no bundled scripts.

It sits in Backend & APIs, covering API design. The repository describes itself as: Professional-grade AI coding toolkit: 94 skills, 44 agents, multi-platform (Claude, Cursor, Windsurf, Copilot, Gemini, Cline, Roo Code, Aider, Augment, Antigravity, Codex CLI… The licence is Apache-2.0.

When your agent uses it

Tasks that involve API design

Example prompts

“Design It Twice”
“Use the design-an-interface skill to generate and compares parallel interface designs (Ousterhout 'Design It Twice')”
“/design-an-interface”

Requirements

Pre-approved tools (allowed-tools): Read, Grep, Glob, Bash, Agent

Workflow steps

5 steps, taken from the step headings in SKILL.md.

Gather Requirements
Generate Designs (Parallel Sub-Agents)
Present Designs
Compare Designs
Synthesize

What it can do on your machine

Read from SKILL.md and the folder at commit d64db2b. It shows what the files ask for, not the result of running them.

Tool permissions
Pre-approves these tools, so the agent can use them without asking each time:
- Read
- Grep
- Glob
- Bash
- Agent
From allowed-tools in the SKILL.md frontmatter.
Runs code
No scripts in the folder and no shell commands in SKILL.md.
From the folder's file list and the shell code blocks in SKILL.md.
Network
No URLs in SKILL.md.
From URLs in SKILL.md, links to its own repository left out.
Credentials
Names no API keys, tokens, secrets or passwords.
From names ending in _API_KEY, _TOKEN, _SECRET, _KEY or _PASSWORD in SKILL.md.

Context cost

Design An Interface loads about 952 tokens when it runs. Until then it costs about 44 tokens; SKILL.md has 433 words of instructions outside code blocks.

Always · name and description, kept in context so the agent knows when to use it: ~44
When it runs · the whole SKILL.md, loaded when a task matches: ~952

Estimates: characters ÷ 4, the usual rule of thumb; real counts depend on the model's tokenizer. Scripts and assets cost tokens only if the agent reads them.

Safety

Auto-check: notes

The automated check noted patterns worth knowing about, such as sudo or a known installer.

NotePre-approves every shell command (allowed-tools: Bash)SKILL.md
```
allowed-tools: Read, Grep, Glob, Bash, Agent
```

Automated static check — not a guarantee. Review scripts before installing. It scans the text of SKILL.md for risky patterns (piping downloads into a shell, reading credential files, hidden Unicode, destructive commands); files beside SKILL.md are not scanned.

SKILL.md

The full file from softspark/ai-toolkit at commit d64db2b, republished under its Apache-2.0 licence (© softspark). 433 words, ~952 tokens.

Download SKILL.mdSave it as .claude/skills/design-an-interface/SKILL.md (or your agent's skills folder).

name: design-an-interface
description: Generates and compares parallel interface designs (Ousterhout 'Design It Twice'). Triggers: design API, interface options, compare modules, design it twice.
allowed-tools: Read, Grep, Glob, Bash, Agent
user-invocable: true
effort: high
argument-hint: [module or interface to design]

Design an Interface

$ARGUMENTS

Generate 3+ radically different interface designs using parallel sub-agents, then compare. Based on "Design It Twice" from "A Philosophy of Software Design."

Usage

/design-an-interface [module or interface to design]

What This Command Does

Gathers requirements and constraints
Spawns 3+ parallel sub-agents with different design constraints
Presents each design with signatures, usage examples, and trade-offs
Compares on simplicity, depth, efficiency, and correctness
Synthesizes best elements into final recommendation

Process

1. Gather Requirements

Before designing, understand:

What problem does this module solve?
Who are the callers? (other modules, external users, tests)
What are the key operations?
Any constraints? (performance, compatibility, existing patterns)
What should be hidden inside vs exposed?

2. Generate Designs (Parallel Sub-Agents)

Spawn 3+ sub-agents simultaneously using Agent tool. Each gets a radically different constraint:

Agent	Constraint
Agent 1	Minimize method count — aim for 1-3 methods max
Agent 2	Maximize flexibility — support many use cases
Agent 3	Optimize for the most common case
Agent 4	Take inspiration from a specific paradigm/library

Each agent outputs:

Interface signature (types/methods)
Usage example (how caller uses it)
What this design hides internally
Trade-offs of this approach

3. Present Designs

Show each design sequentially so user can absorb each approach before comparison:

Interface signature — types, methods, params
Usage examples — how callers actually use it
What it hides — complexity kept internal

4. Compare Designs

Compare in prose (not tables) on:

Criterion	Description
Interface simplicity	Fewer methods, simpler params
General-purpose vs specialized	Flexibility vs focus
Implementation efficiency	Does shape allow efficient internals?
Depth	Small interface hiding significant complexity (good) vs large interface with thin implementation (bad)
Ease of correct use	vs ease of misuse

Show full SKILL.md (156 more words)Show less

5. Synthesize

Often the best design combines insights from multiple options. Give an opinionated recommendation. Ask:

Which design best fits the primary use case?
Any elements from other designs worth incorporating?

Visual Companion (Optional)

When upcoming design explorations will involve visual content (mockups, layout comparisons, architecture diagrams), offer the browser companion:

"Some of these interface designs might be easier to compare visually. I can show diagrams and side-by-side comparisons in a browser. Want to try it?"

This offer MUST be its own message. Do not combine with other questions. Wait for response.

If accepted, start the server and use it for visual comparisons only. Text/conceptual questions stay in terminal.

See ../write-a-prd/reference/visual-companion.md for details.

Anti-Patterns

Don't let sub-agents produce similar designs — enforce radical difference
Don't skip comparison — the value is in contrast
Don't implement — this is purely about interface shape
Don't evaluate based on implementation effort

READ-ONLY

This skill designs interfaces. It does NOT write implementation code.

Files

Just SKILL.md in app/skills/design-an-interface of softspark/ai-toolkit.

Open the folder on GitHubat commit d64db2b

Compare with similar skills

Design An Interface next to the 5 skills that share the most tags, products or categories with it. Stars are the repository's; “used in” counts other GitHub owners with a copy.

Design An Interface compared with similar skills
Skill	Stars	Used in	Tokens	Auto-check	Licence	Repo updated
Design An Interface this skillsoftspark/ai-toolkit	179	—	~952	Automated safety check: Notes	Apache-2.0	yesterday
API DesignerJeffallan/claude-skills	12k	2 repos	~2k	Automated safety check: Pass	MIT	4 days ago
Nodejs Backend Patternsever-works/ever-works	158	18 repos	~4k	Automated safety check: Pass	AGPL-3.0	2 days ago
Pangolin CRUD Endpointsfosrl/pangolin	23k	—	~461	Automated safety check: Pass	Custom licence	today
API Design Principlesjh941213/my-cc-harness	126	20 repos	~3.4k	Automated safety check: Pass	None	2 mo ago
Backend PatternshellangleZ/burn-in-cceverywhere-ralph	112	17 repos	~3.3k	Automated safety check: Pass	None	8 mo ago

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Questions about Design An Interface

What does Design An Interface do?

Generates and compares parallel interface designs (Ousterhout 'Design It Twice'). Design An Interface is an agent skill from softspark/ai-toolkit. Generates and compares parallel interface designs (Ousterhout 'Design It Twice').

When should I use Design An Interface?

Design An Interface fits situations like: tasks that involve API design.

How do I install Design An Interface in Claude Code?

Run `npx skills add softspark/ai-toolkit --skill design-an-interface -a claude-code`. Or copy the skill folder (app/skills/design-an-interface in softspark/ai-toolkit) into .claude/skills/design-an-interface in your project. Claude Code loads it when a task matches its description.

How do I install Design An Interface in Codex?

Run `npx skills add softspark/ai-toolkit --skill design-an-interface -a codex`. Or copy the skill folder (app/skills/design-an-interface in softspark/ai-toolkit) into .agents/skills/design-an-interface in your project. Codex loads it when a task matches its description.

Can I use Design An Interface in Cursor, Gemini CLI or GitHub Copilot?

Cursor, Gemini CLI, GitHub Copilot and OpenCode also load SKILL.md folders. With the skills CLI, run `npx skills add softspark/ai-toolkit --skill design-an-interface -a cursor` (or -a gemini-cli, github-copilot or opencode for the others). To copy it by hand, put the folder in .cursor/skills/design-an-interface, .gemini/skills/design-an-interface, .github/skills/design-an-interface and .opencode/skills/design-an-interface in your project.

What does Design An Interface need to run?

SKILL.md names no scripts, command-line tools or credentials: Design An Interface is instructions for the agent only. Its frontmatter pre-approves these tools: Read, Grep, Glob, Bash, Agent.

Does Design An Interface access the network?

SKILL.md contains no URLs. Any network use would come from the scripts or tools the agent runs. This is read from the text; nothing was executed.

Is Design An Interface safe to install?

Our automated static check of SKILL.md found notes only (pre-approves every shell command (allowed-tools: bash)), nothing it rates as a warning. It is not a guarantee. Review the folder before installing.

What licence does Design An Interface use?

Design An Interface is published under the Apache-2.0 licence (the repository's licence). It allows redistribution, so the full SKILL.md is shown on this page.

How many tokens does Design An Interface use?

About 952 tokens (SKILL.md is roughly 3.8k characters). Agents keep only the skill's name and description in context until a task matches; then they load SKILL.md in full.

What are the alternatives to Design An Interface?

Skills that share tags, products or a category with Design An Interface: API Designer (Jeffallan/claude-skills, 12k stars), Nodejs Backend Patterns (ever-works/ever-works, 158 stars), Pangolin CRUD Endpoints (fosrl/pangolin, 23k stars) and API Design Principles (jh941213/my-cc-harness, 126 stars). The comparison table on this page puts their stars, adoption, token cost, safety result and licence side by side.

Who maintains Design An Interface?

softspark (a GitHub user) maintains it in softspark/ai-toolkit, which has 179 GitHub stars. The repository holds 112 skills in this directory. The repository was last updated on October 7, 2026.

Source: softspark/ai-toolkit on GitHub. Facts on this page come from the repository at the commit we read; the author's words are quoted as theirs.

Install Design An Interface

Facts

At a glance

What it does

When your agent uses it

Example prompts

Requirements

Workflow steps

What it can do on your machine

Tool permissions

Runs code

Network

Credentials

Context cost

Safety

SKILL.md

Design an Interface

Usage

What This Command Does

Process

1. Gather Requirements

2. Generate Designs (Parallel Sub-Agents)

3. Present Designs

4. Compare Designs

5. Synthesize

Visual Companion (Optional)

Anti-Patterns

READ-ONLY

Files

Compare with similar skills

Similar skills

More from softspark/ai-toolkit

Related

Questions about Design An Interface