design

A guided system-design process that brings together architecture, security, and operations concerns and writes files for separate workstreams.

In plain words
What is it for?
Use it to clarify components, data, security, monitoring, scope, and acceptance criteria for a planned feature.
Why use it?
It helps turn a feature idea into defined work before implementation, while checking existing drafts and related tasks.

Skill for Claude CodeCodex

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/fall-out-bug/sdp/design
Any agent
npx skills add fall-out-bug/sdp --skill design
Clone the repo
git clone --depth 1 https://github.com/fall-out-bug/sdp

Made for: Claude Code, Codex.

Per session 12 Skills are progressive disclosure: only the name and description are preloaded; the body loads when the skill is used.
When invoked 1,269 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 $0.00012 $0.01269
Opus 5 $0.00006 $0.00634
Sonnet 5 $0.00002 $0.00254
Haiku 4.5 $0.00001 $0.00127

Measured 2d ago against content hash 7bc239b9ce72, method: parsed. Prices are Anthropic first-party input rates as of 2026-08-30, from the pricing page.

Security

Grade A, and why

design 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 2d 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.

prompts/skills/design/SKILL.md · 150 lines

How it starts

The opening of the file, as written. The whole thing — 150 lines — stays where its author put it; the contents beside it link to each section on GitHub.

@design

Multi-agent design (Arch + Security + SRE) with progressive discovery blocks.

When to Use

After @idea, or directly from a feature description. Creates workstream files with AC and scope.

Pre-flight

Before creating draft: ls docs/drafts/idea-* — do not duplicate. If an idea draft already covers this topic, reuse or extend it instead of creating a new one.

Beads from review: In scope by default. Mark OOS only with explicit justification (e.g. "duplicate", "superseded by prior work").

Workflow

1. Load requirements

  • docs/intent/{task_id}.json or docs/drafts/idea-*.md if available
  • Or: use the feature description directly

2. Progressive discovery — unless --quiet

3-5 discovery blocks, 2-3 questions each:

  • Architecture: What components change? What's the data model?
  • Security: Any auth, crypto, or boundary concerns?
  • Operations: Any monitoring, logging, or CI concerns?

After each block: Continue / Skip / Done

3. Generate workstream files

When source is beads (review findings): For each bead, run bd show <id> and grep the codebase for the fix. If already fixed, run bd close <id> and remove from scope. Do not create WS for beads that are already addressed.

Create docs/workstreams/backlog/00-FFF-SS.md for each deliverable.

Required sections:

# 00-FFF-SS: Feature Name — Step Description

Feature: FFFF (sdp_dev-XXXX)
Phase: N
Status: Backlog

## Goal

One paragraph: what and why.

## Scope Files

List exact file paths or directory prefixes this workstream touches.
Used by sdp-guard for boundary checking and CI scope-compliance.

- internal/evidence/
- cmd/sdp-evidence/main.go

## Dependencies

- 00-FFF-01: prerequisite workstream (if any)

## Acceptance Criteria

Specific, testable, binary (pass/fail):

- [ ] Criterion 1
- [ ] Criterion 2
- [ ] go build ./... passes
- [ ] go test ./internal/evidence/... passes

4. Create Beads issues

bd create --title="WS FFF-SS: Short title" --type=task

Read the full file on GitHub · 150 lines

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. 2d ago First seen · 150 lines · 12 tokens per session scan A 7bc239b9ce72

Subscribe to this mod's changes

design is a skill published in the GitHub repository fall-out-bug/sdp (19 stars, last pushed 2mo ago), licensed MIT. It adds 12 tokens to every session and 1,269 once invoked, about $0.0001 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 2026-08-30.