C4 Diagramming

What it does

When your agent uses it

• Teams need a communication-ready system context
• Code-level view
• Including audience
• Mermaid syntax/rendering work without C4 modeling

Example prompts

• “/c4-diagramming”

Requirements

• Docker
• Compatibility (from SKILL.md): Mermaid or Structurizr tooling is optional and only needed to render or validate diagrams.

What it can do on your machine

Read from SKILL.md and the folder at commit 22b4723. It shows what the files ask for, not the result of running them.

• Tool permissions

  Pre-approves nothing: there is no allowed-tools line, so your agent's usual permission prompts apply.

  From allowed-tools in the SKILL.md frontmatter.

• Runs code

  No scripts in the folder and no shell commands in SKILL.md.

  From the folder's file list and the shell code blocks in SKILL.md.

• Network

  Links to these hosts (documentation or services it may open):

  • github.com
  • c4model.com

  From URLs in SKILL.md, links to its own repository left out.

• Credentials

  Names no API keys, tokens, secrets or passwords.

  From names ending in _API_KEY, _TOKEN, _SECRET, _KEY or _PASSWORD in SKILL.md.

• Compatibility

  Mermaid or Structurizr tooling is optional and only needed to render or validate diagrams.

  From compatibility in the SKILL.md frontmatter.

Context cost

C4 Diagramming loads about 2k tokens when it runs, and up to ~8.9k if it reads all its reference files. Until then it costs about 105 tokens; SKILL.md has 789 words of instructions outside code blocks.

Always · name and description, kept in context so the agent knows when to use it

~105

When it runs · the whole SKILL.md, loaded when a task matches

~2k

With references · SKILL.md plus every file in references/, read only if the agent opens them

~8.9k

Estimates: characters ÷ 4, the usual rule of thumb; real counts depend on the model's tokenizer. Scripts and assets cost tokens only if the agent reads them.

Safety

Automated static check — not a guarantee. Review scripts before installing. It scans the text of SKILL.md for risky patterns (piping downloads into a shell, reading credential files, hidden Unicode, destructive commands); files beside SKILL.md are not scanned.

SKILL.md

The full file from magnus919/agent-skills at commit 22b4723, republished under its MIT licence (© magnus919). 789 words, ~1,971 tokens.

name

c4-diagramming

description

Create and review C4 software-architecture diagrams using Mermaid or Structurizr. Use when teams need a communication-ready system context, container, component, or code-level view, including audience, narrative, hierarchy, labels, legends, accessibility, and uncertainty. Do not use for Mermaid syntax/rendering work without C4 modeling, architecture decisions, or full accessibility conformance reviews.

compatibility

Mermaid or Structurizr tooling is optional and only needed to render or validate diagrams.

license

MIT

metadata.source_repo

https://github.com/magnus919/hermes-profiles

metadata.source_commit

867a555

workspace {
    model {
        user = person "Customer"
        system = softwareSystem "Your System" {
            webapp = container "Web Application" "TypeScript, React"
            api = container "API" "Go"
            db = container "Database" "PostgreSQL"
            user -> webapp "Uses"
            webapp -> api "Makes API calls"
            api -> db "Reads/writes"
        }
    }
    views {
        systemContext system { include * autolayout lr }
        container system { include * autolayout lr }
        component api { include * autolayout lr }
        theme default
    }
}

© magnus919, MIT. Rendered from Markdown: HTML in the file is shown as text, images as links, and headings moved down two levels. Raw file

Files

SKILL.md and 7 other files (references) in c4-diagramming of magnus919/agent-skills.

• SKILL.md
• README.md
• evals/evals.json
• references/architecture-as-code-ecosystem.md
• references/c4-to-pyramid-mapping.md
• references/ci-pipeline-templates.md
• references/source-index.md
• references/technical-diagram-communication.md

Open the folder on GitHubat commit 22b4723