design-doc

design-doc is a skill for Claude Code, Codex from sananthanarayan/skilldrop. It costs 59 tokens per session (758 once invoked), scanned A, original, MIT.

A skill for turning a feature brief into a structured engineering design document. The document covers the problem, goals, alternatives, chosen approach, risks, rollout, and open questions.

In plain words
What is it for?
Use it for technical proposals, one-page plans, and design reviews when the team needs to compare options and agree on an approach.
Why use it?
It gives an engineering team a common document for reviewing a proposed change and makes missing context—especially why the work is needed now—visible.

Skill for Claude CodeCodex

Part of the skilldrop plugin — 51 skills, 4 agents shipped together

Install

Getting it into your agent

One page per mod, every tool's command on it. A separate URL per tool would split the same page into five that compete with each other.

agentmods
npx agentmods add skills/sananthanarayan/skilldrop/design-doc
Any agent
npx skills add sananthanarayan/skilldrop --skill design-doc
Clone the repo
git clone --depth 1 https://github.com/sananthanarayan/skilldrop

Made for: Claude Code, Codex.

Or install skilldrop, the plugin that ships this one along with the rest of its 51 skills, 4 agents.

Wrote this? Show the measurements

A badge with what this costs and how it scanned, read live from this page, so it follows the numbers instead of freezing them. Markdown for a README, HTML for a documentation site or a project page.

agentmods badge for design-doc

README.md
[![agentmods](https://agentmods.dev/badge/skills/sananthanarayan/skilldrop/design-doc.svg)](https://agentmods.dev/skills/sananthanarayan/skilldrop/design-doc)
Your own site
<a href="https://agentmods.dev/skills/sananthanarayan/skilldrop/design-doc"><img src="https://agentmods.dev/badge/skills/sananthanarayan/skilldrop/design-doc.svg" alt="Measured on agentmods" height="20"></a>
Per session 59 Skills are progressive disclosure: only the name and description are preloaded; the body loads when the skill is used.
When invoked 758 The whole file, excluding the scripts and references it only reads on demand.
Security scan A 0 findings. Scan, not verified.
Origin original No closer match found in the catalogue.
Token cost

What it costs to keep this loaded

Counted locally with the o200k_base tokenizer, which is exact for GPT models; Claude uses its own tokenizer and its counts differ. Treat this as one consistent yardstick across the catalogue rather than a bill. Prices are per million input tokens.

ModelPer sessionOnce invoked
Fable 5.1 $0.00059 $0.00758
Opus 5 $0.00030 $0.00379
Sonnet 5 $0.00012 $0.00152
Haiku 4.5 $0.00006 $0.00076

Measured 5d ago against content hash d57e2b32a836, method: parsed. Prices are Anthropic first-party input rates as of 2026-09-05, from the pricing page.

Security

Grade A, and why

design-doc scanned grade A with 0 findings against 26 rules in 11 categories — prompt injection, anti-refusal, data exfiltration, privilege escalation, supply chain, agent snooping, system-prompt leakage, SSRF and excessive agency — measured 5d ago.

A static scan of the body, not an audit. Every finding is printed with the line that produced it so you can judge whether it matters here. A mod is markdown that instructs an agent; that is exactly why what it instructs is worth reading.

Nothing flagged

None of the 26 patterns this scan looks for appear in this file: no shell pipes, no recursive deletes, no credential paths, no hidden text, no instruction-override or anti-refusal phrasing, no agent-config snooping. That is not a guarantee, it is the absence of the things that are checkable.

skills/design-doc/SKILL.md · 50 lines

How it starts

The opening of the file, as written. The whole thing — 50 lines — stays where its author put it; the contents beside it link to each section on GitHub.

design-doc

You help the user turn a feature brief into a structured design doc that an engineering team can review and approve.

How to respond

  1. Understand the brief. Make sure you know:

    • What we're building (one sentence)
    • Who's affected (users, callers, teams)
    • Why now (the forcing function — outage, regulatory, competitor, scaling cliff)

    If any of these are missing, ask. Don't draft a design doc without a why now.

  2. Default to the standard structure in templates/design-doc.md:

    1. Title + status (Draft / In Review / Approved) + author + date
    2. TL;DR — three bullets, readable in 30 seconds
    3. Context — why is this being proposed
    4. Goals / Non-goals — explicit non-goals matter as much as goals
    5. Proposal — the actual design (this is the longest section)
    6. Alternatives considered — at least 2 alternatives with why-not
    7. Risks & mitigations
    8. Rollout plan — staged rollout, feature flag, rollback criteria
    9. Open questions
  3. Length discipline. A good design doc is 2–5 pages rendered. If you blow past that, you're either solving too many problems in one doc or writing reference material that belongs elsewhere.

  4. Show, don't tell. Where the design is structural, embed a Mermaid diagram (use the architecture-diagrams skill if needed). Where it's about flows, embed a sequence diagram. Where it's about API shape, embed a small example request/response.

  5. End with explicit asks. The "Open questions" section is where the doc earns its keep — list the real unresolved questions, with the names of people who should answer them.

Quality bar

  • Non-goals are real, not throat-clearing. If your non-goals list reads "we're not solving world hunger", delete it. Good non-goals are things a reasonable reader might assume you are doing ("not migrating existing customers in v1").
  • Alternatives have a why-not, not just a description. Two sentences each: what is it, why didn't we pick it.
  • Risks have mitigations. A bare list of "things that could go wrong" is anxiety, not engineering.
  • Rollout criteria are concrete. "We'll monitor closely" is not a criterion. "Roll forward to 100% if p99 < 80ms for 48h after 10% rollout" is.

Read the full file on GitHub · 50 lines

Files

What ships with it

4 files beside SKILL.md in the same directory: the scripts, references and assets a skill reads on demand. Not counted in the per-session cost; read them before you install if any of them is executable.

Changes

What this file has done since we first saw it

Hashed on every crawl. A supply-chain change to an agent config is a question of when, not whether, so the history is kept rather than the latest state alone.

  1. 5d ago First seen · 50 lines · 59 tokens per session scan A d57e2b32a836

Subscribe to this mod's changes

design-doc is a skill published in the GitHub repository sananthanarayan/skilldrop (2 stars, last pushed 21d ago), licensed MIT. It adds 59 tokens to every session and 758 once invoked, about $0.0003 per session on Opus 5. A static security scan graded it A with 0 findings. No closer match exists in the catalogue, so it is treated as the original; first seen 2026-08-31.

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