design

A technical-design workflow step that turns an approved product plan into architecture choices, including what to build or buy. It also records design decisions for review.

In plain words
What is it for?
Use it to compare build-versus-buy options, choose infrastructure and technologies, record architecture decisions, and approve the design.
Why use it?
It gives the project a structured way to decide how the system should be built before implementation begins. It also prevents technical design from starting before the MVP plan is approved.

Command

Part of the haytham plugin — 7 skills, 7 commands, 12 agents, 2 hooks 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 commands/arslan70/haytham/design
Clone the repo
git clone --depth 1 https://github.com/arslan70/haytham

Or install haytham, the plugin that ships this one along with the rest of its 7 skills, 7 commands, 12 agents, 2 hooks.

Per session 16 Only the description is in the session, so the agent can decide to use it. The body loads when it is invoked.
When invoked 1,205 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 $0.00016 $0.01205
Opus 5 $0.00008 $0.00602
Sonnet 5 $0.00003 $0.00241
Haiku 4.5 $0.00002 $0.00120

Measured 3d ago against content hash 57ba28df9a5c, 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 3d 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.

commands/design.md · 105 lines

How it starts

The opening of the file, as written. The whole thing — 105 lines — stays where its author put it; the contents beside it link to each section on GitHub.

Haytham: Technical Design (Phase 3 - HOW)

You are running Phase 3 of the Haytham validation workflow. This phase decides on infrastructure and architecture.

IMPORTANT: Always read agent output from files, not from conversation history.

Progress Tracking

After prerequisites pass, call TodoWrite once with:

  1. Step 1 — Architecture (build/buy, decisions, research directives)
  2. Step 2 — Review
  3. Step 3 — Gate 3

Mark each todo in_progress when its step begins and completed when its output file is written or its gate decision is recorded.

Prerequisites

Verify .haytham/session/phase-2-what/gate-decision.json exists. If it doesn't, tell the user:

"Phase 2 (MVP specification) must be completed first. Run /haytham:specify to start."

Roadmap

Before launching any agents, tell the user:

Phase 3: Technical Design

This will run 3 steps:

  1. Architecture — build/buy analysis and technology decisions (~2 min)
  2. Review — you review the architecture
  3. Gate 3 — you approve the design ← YOU DECIDE HERE

Estimated total: ~3 minutes.

Step 1: Architecture

Create .haytham/session/phase-3-how/ directory if it doesn't exist.

Tell the user:

Step 1/3: Architecture Deciding what to build, what to buy, and how the pieces fit together.

Launch an architect agent with this task:

Read capabilities from .haytham/session/phase-2-what/capabilities.json, MVP scope from .haytham/session/phase-2-what/mvp-scope.md, and system traits from .haytham/session/phase-2-what/system-traits.json. Produce build/buy analysis, architecture decisions, research directives, and the founder-facing gate summary. Write to .haytham/session/phase-3-how/build-buy.json, .haytham/session/phase-3-how/architecture-decisions.json, .haytham/session/phase-3-how/research-directives.json, and .haytham/session/phase-3-how/gate-summary.md.

After the agent completes, read .haytham/session/phase-3-how/build-buy.json, .haytham/session/phase-3-how/architecture-decisions.json, and .haytham/session/phase-3-how/research-directives.json and present a structured digest:

Read the full file on GitHub · 105 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. 3d ago First seen · 105 lines · 16 tokens per session scan A 57ba28df9a5c

Subscribe to this mod's changes

design is a command published in the GitHub repository arslan70/haytham (13 stars, last pushed 1mo ago), licensed MIT. It adds 16 tokens to every session and 1,205 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.