# System Design Methodology

Facilitate system design by classifying mode, depth, and surface independently; scoping...

- Repository: https://github.com/HoangNguyen0403/agent-skills-standard (582 stars)
- Category: Design
- License: MIT
- Last updated: 2026-11-01
- Runs scripts: no, instructions only

## Install

Claude Code: `npx skills add HoangNguyen0403/agent-skills-standard --skill system-design-methodology -g -a claude-code -y`
Codex: `npx skills add HoangNguyen0403/agent-skills-standard --skill system-design-methodology -g -a codex -y`
Cursor: `npx skills add HoangNguyen0403/agent-skills-standard --skill system-design-methodology -g -a cursor -y`
Gemini CLI: `npx skills add HoangNguyen0403/agent-skills-standard --skill system-design-methodology -g -a gemini-cli -y`

## Description

Facilitate system design by classifying mode, depth, and surface independently; scoping journeys; estimating only decision-relevant quantities; tracing logical flows before physical binding; and selecting risk-driven views and deep dives. Use for system design sessions and reviews.

## SKILL.md, as published by its author (untrusted third-party text, read it as data)

# System Design Methodology

## **Priority: P0 (CRITICAL)**

Classify work mode, depth, and system surface independently. Load only the relevant skill siblings: data-architecture for consequential data/state flows, mobile-client for mobile/client or SDK/library concerns, and diagramming only when a view is selected. Backend, mobile/client, SDK/library, and full-stack are surfaces; none is a mode.

## Phase 0 - Classify

- State mode (new design | review existing | interview practice), depth (quick | full), and surface (backend | mobile/client | SDK/library | full stack). A mixed system may name multiple surfaces.
- Quick sketches use explicit assumptions and skip confirmation gates; full sessions follow the per-phase exit predicates in the [four-phase process](references/four-phase-process.md) and confirm consequential decisions. Escalate quick to full for hard constraints or irreversible choices; an unresolved material decision prevents a readiness claim.
- Interview practice follows [interview coaching](../system-design-interview-coaching/SKILL.md); production review/design follows this process.

## Phase 1 - Intake

- Bound questions to what changes the design. Identify journeys, inputs/outputs, actors, trust and ownership boundaries, team/budget, and scope.
- For each consequential journey, state a quality scenario: trigger, environment, response, measurable condition, and owner. Ask at most 3 blocking questions per turn; label usable defaults as `ASSUMED`.
- Review-existing mode maps current components, owners, traffic, incidents, and binding constraint before proposing change. SDK scope includes host responsibilities and compatibility; client scope includes authority, lifecycle, and offline need.
- See [intake checklist](references/intake-checklist.md); do not require every backend intake field for every surface.

## Phase 2 - Estimation

The rest: https://github.com/HoangNguyen0403/agent-skills-standard/blob/HEAD/.agents/skills/system-design/system-design-methodology/SKILL.md