C4 Architecture Diagram

---
name: c4-architecture-diagram
description: Turn a system description into a simple diagram and clear notes about what is unknown.
license: MIT
compatibility: Works in any Agent Skills-compatible harness that can format Markdown and Mermaid.
allowed-tools: Read
metadata:
  author: Web3 Energy
  category: architecture
  tags: architecture,diagrams,documentation
---
# C4 Architecture Diagram

## When to use
Use when a person supplies a system description and wants a high-level C4 context or container diagram. Ask for the system boundary, users, external systems, and important containers if the description is too thin.

## Steps
1. Extract actors, the system boundary, external dependencies, containers, and the purpose of each connection from supplied facts.
2. Separate confirmed facts from assumptions; do not invent services, protocols, or ownership.
3. Choose one C4 level that answers the request. Keep the diagram readable and label each relationship with its known purpose or protocol.
4. For Mermaid C4, use function syntax for declarations and relationships, for example:

   ```mermaid
   C4Context
   Person(reader, "Library Reader")
   System(library, "Library Service")
   System_Ext(identity, "Identity Provider")
   Rel(reader, library, "searches catalog")
   ```

   Use `System_Boundary(id, "name")` and `Container(id, "name")` when the supplied facts require a container view. Preserve requested identifiers and return only the requested diagram when asked.

## Output
Return a Mermaid diagram, then a short legend, assumptions, and open questions when the user asks for them. Do not append notes when the task asks for only the diagram.

## Limits
Do not inspect a repository, call services, infer deployment topology, or claim the diagram is complete unless the user supplies that evidence. Keep secrets and personal data out of diagram labels.

## Example

Before: “A shop app has users and sends orders to a warehouse.”
After: “Person → Shop app → Warehouse · order flow (from the supplied description).”

## Check your result
Before responding, check:
- Every actor, system, and connection comes from the supplied description or is marked as an assumption.
- The diagram uses the requested C4 level and does not claim to show missing details.

Tell the person which checks passed and what remains uncertain. Ask them to answer Yes or No about whether it worked, and give this report link: https://skills.web3-energy.com/skills/c4-architecture-diagram. If they downloaded this skill, ask them to open the link in the same browser used for the download so its version-bound install token is recognized. Never count your own checks as a human report or claim the person reported anything.