C4 Architecture
Writes C4 Context/Container/Component/Deployment diagrams as Mermaid into docs/architecture/
Test report
- Verdict
- Works with setup
- Score
- Tested
- Jul 21, 2026
- Environment
- Claude Code 2.x (agent harness)
- Upstream re-checked
- Aug 10, 2026 · ed972bc
Located skills/c4-architecture/SKILL.md (295 lines) via the GitHub tree API; frontmatter parses with name+description, and all three body-referenced files fetched HTTP 200 (references/c4-syntax.md 14564 B, common-mistakes.md 12441 B, advanced-patterns.md 18346 B), as did README.md. Pure markdown, zero scripts; grep for curl|wget|base64|eval|api_key|"ignore previous" across SKILL.md and all references returned nothing, and the only path it writes to is the relative docs/architecture/. Trigger phrasings judged: SHOULD fire — "Draw a C4 container diagram for this repo's services", "I need to document the architecture of our payment platform for new hires", "Can you make a deployment diagram showing our ECS + RDS setup" (all yes, 3/3 correct); SHOULD NOT fire — "Refactor OrderService to remove the circular dependency between modules" (code change, no diagram) and "Draw a sequence diagram in Mermaid for the checkout flow" (Mermaid but not a C4 level; the description enumerates only context/container/component/deployment) — both correctly declined, 5/5. Output test: I wrote a baseline C4Container diagram for a URL shortener before opening the body, then redid it under the skill; the skill version added the mandated Context diagram as a second file under the documented c4-context.md / c4-containers.md naming, replaced 3 generic edge labels ("Uses", "Calls", "Reads/Writes") with action-verb labels carrying a technology tag on all 5 edges, upgraded aliases from web/api/db/cache to meaningful ones, and added UpdateLayoutConfig — real but bounded improvement, since the baseline was already valid renderable Mermaid. Docs lose a point for the README claiming it "automatically selects the right level of detail for your audience" when that is a lookup table the model consults, not automation.
Scored on four weighted criteria — install, triggering, output vs. baseline, docs. How scoring works
- Installs cleanly 5/5
- Triggers reliably 5/5
- Output vs. baseline 5/10
- Docs & honesty 4/5
What C4 Architecture does
Generates software architecture documentation as Mermaid C4 diagrams at four abstraction levels (Context, Container, Component, Deployment) plus Dynamic request-flow diagrams, and writes them to docs/architecture/ under a fixed naming convention. It carries the full Mermaid C4 element and relationship syntax, a level-selection table keyed to audience, and rules such as unidirectional arrows, action-verb edge labels, technology tags on every relationship, and a 20-element ceiling per diagram. Triggers on requests to create an architecture diagram, C4 diagram, system context, container, component or deployment diagram, or to document or visualize system architecture.
How to install C4 Architecture
git clone --depth 1 https://github.com/softaworks/agent-toolkit.git /tmp/c4-architecture-src
mkdir -p ~/.claude/skills
cp -R /tmp/c4-architecture-src/skills/c4-architecture ~/.claude/skills/c4-architecture
# Claude Code plugin instead: /plugin marketplace add softaworks/agent-toolkit
# then /plugin install c4-architecture@agent-toolkit
# Pure markdown, no scripts or extra dependencies.
Skills live in ~/.claude/skills/ (global) or .claude/skills/
(per-project). Restart Claude Code after installing.
Commands — how to trigger C4 Architecture
-
/c4-architectureWrites C4 Context/Container/Component/Deployment diagrams as Mermaid into docs/architecture/
It also activates on plain-language prompts like these:
-
Create a C4 context diagram for this system -
Document our architecture with a container diagram -
Generate a component diagram for this service
Frequently asked questions
- Is the C4 Architecture skill free?
- Yes. The skill itself is free from softaworks/agent-toolkit. SkillProof publishes the install command and an independent test verdict at no cost.
- Does C4 Architecture work with Claude Code?
- We tested it with Claude Code 2.x (agent harness) on Jul 21, 2026. Verdict: Works with setup. Located skills/c4-architecture/SKILL.md (295 lines) via the GitHub tree API; frontmatter parses with name+description, and all three body-referenced files fetched HTTP 200 (references/c4-syntax.md 14564 B, common-mistakes.md 12441 B, advanced-patterns.md 18346 B), as did README.md. Pure markdown, zero scripts; grep for curl|wget|base64|eval|api_key|"ignore previous" across SKILL.md and all references returned nothing, and the only path it writes to is the relative docs/architecture/. Trigger phrasings judged: SHOULD fire — "Draw a C4 container diagram for this repo's services", "I need to document the architecture of our payment platform for new hires", "Can you make a deployment diagram showing our ECS + RDS setup" (all yes, 3/3 correct); SHOULD NOT fire — "Refactor OrderService to remove the circular dependency between modules" (code change, no diagram) and "Draw a sequence diagram in Mermaid for the checkout flow" (Mermaid but not a C4 level; the description enumerates only context/container/component/deployment) — both correctly declined, 5/5. Output test: I wrote a baseline C4Container diagram for a URL shortener before opening the body, then redid it under the skill; the skill version added the mandated Context diagram as a second file under the documented c4-context.md / c4-containers.md naming, replaced 3 generic edge labels ("Uses", "Calls", "Reads/Writes") with action-verb labels carrying a technology tag on all 5 edges, upgraded aliases from web/api/db/cache to meaningful ones, and added UpdateLayoutConfig — real but bounded improvement, since the baseline was already valid renderable Mermaid. Docs lose a point for the README claiming it "automatically selects the right level of detail for your audience" when that is a lookup table the model consults, not automation.
- What is the C4 Architecture SkillProof Score?
- 7.6/10 — installs cleanly 5/5, triggers reliably 5/5, output vs. baseline 5/10, docs & honesty 4/5.
- How do I install C4 Architecture?
- Copy the install command from this page, run it in your terminal, and restart Claude Code. Skills live in ~/.claude/skills/ (global) or .claude/skills/ inside a project.
- Can I use C4 Architecture with Cursor, Copilot, Gemini CLI, Codex or other AI tools?
- The SKILL.md format is native to Claude (Claude Code, Desktop, claude.ai). The instructions inside adapt to other assistants: Cursor rules, GitHub Copilot instructions, Windsurf rules, Custom GPTs, AGENTS.md for OpenAI Codex, and GEMINI.md for Google Gemini CLI — our conversion guides cover each, and the free converter on the tools page does the wrapping for you.