diagramming-code

SKILL.md

Diagramming Code

Generates Mermaid diagrams from Trailmark's code graph. A pre-made script
handles Mermaid syntax generation; Claude selects the diagram type and
parameters.

When to Use

Visualizing call paths between functions

Drawing class inheritance hierarchies

Mapping module import dependencies

Showing class structure with members

Highlighting complexity hotspots with color coding

Tracing data flow from entrypoints to sensitive functions

When NOT to Use

Querying the graph without visualization (use the trailmark skill)

Mutation testing triage (use the genotoxic skill)

Architecture diagrams not derived from code (draw by hand)

Prerequisites

trailmark must be installed. If uv run trailmark fails, run:

uv pip install trailmark

DO NOT fall back to hand-writing Mermaid from source code reading. The
script uses Trailmark's parsed graph for accuracy. If installation fails,
report the error to the user.

Quick Start

uv run {baseDir}/scripts/diagram.py \
    --target {targetDir} --language auto --type call-graph \
    --focus main --depth 2

Output is raw Mermaid text. Wrap in a fenced code block:

```mermaid
flowchart TB
    ...
```

Diagram Types

├─ "Who calls what?"               → --type call-graph
├─ "Class inheritance?"             → --type class-hierarchy
├─ "Module dependencies?"           → --type module-deps
├─ "Class members and structure?"   → --type containment
├─ "Where is complexity highest?"   → --type complexity
└─ "Path from input to function?"   → --type data-flow

For detailed examples of each type, see
references/diagram-types.md.

Workflow

Diagram Progress:
- [ ] Step 1: Verify trailmark is installed
- [ ] Step 2: Identify diagram type from user request
- [ ] Step 3: Determine focus node and parameters
- [ ] Step 4: Run diagram.py script
- [ ] Step 5: Verify output is non-empty and well-formed
- [ ] Step 6: Embed diagram in response

Step 1: Run uv run trailmark analyze --language auto --summary {targetDir}. Install
if it fails. Then run pre-analysis via the programmatic API:

from trailmark.query.api import QueryEngine

engine = QueryEngine.from_directory("{targetDir}", language="auto")
engine.preanalysis()

Pre-analysis enriches the graph with blast radius, taint propagation,
and privilege boundary data used by data-flow diagrams.

If auto-detection is wrong for the target, rerun with an explicit language or
comma-separated list such as python,rust.

Step 2: Match the user's request to a --type using the decision tree
above.

Step 3: For call-graph and data-flow, identify the focus function.
Default --depth 2. Use --direction LR for dependency flows.

Step 4: Run the script and capture stdout.

Step 5: Check: output starts with flowchart or classDiagram,
contains at least one node. If empty or malformed, consult
references/mermaid-syntax.md.

Step 6: Wrap output in ```mermaid ``` code fence.

Script Reference

uv run {baseDir}/scripts/diagram.py [OPTIONS]

Argument
Short
Default
Description

--target
-t
required
Directory to analyze

--language
-l
python
Source language

--type
-T
required
Diagram type (see above)

--focus
-f
none
Center diagram on this node

--depth
-d
2
BFS traversal depth

--direction

TB
Layout: TB (top-bottom) or LR (left-right)

--threshold

10
Min complexity for complexity type

Examples

# Call graph centered on a function
uv run {baseDir}/scripts/diagram.py -t src/ -T call-graph -f parse_file

# Class hierarchy for a Rust project
uv run {baseDir}/scripts/diagram.py -t src/ -l rust -T class-hierarchy

# Module dependency map, left-to-right
uv run {baseDir}/scripts/diagram.py -t src/ -T module-deps --direction LR

# Class members
uv run {baseDir}/scripts/diagram.py -t src/ -T containment

# Complexity heatmap (threshold 5)
uv run {baseDir}/scripts/diagram.py -t src/ -T complexity --threshold 5

# Data flow from entrypoints to a specific function
uv run {baseDir}/scripts/diagram.py -t src/ -T data-flow -f execute_query

Customization

Direction: Use TB (default) for hierarchical views, LR for
left-to-right flows like dependency chains.

Depth: Increase --depth to see more of the call graph. Decrease to
reduce clutter. The script warns if the diagram exceeds 100 nodes.

Focus: Always use --focus for call-graph on non-trivial codebases.
For data-flow, omitting focus auto-targets the top 10 complexity hotspots.

Language: Prefer --language auto for polyglot or unfamiliar repos.
Use an explicit language only when you know the target is single-language or
you need to exclude unrelated components.

Supporting Documentation

references/diagram-types.md -
Detailed docs and Mermaid examples for each diagram type

references/mermaid-syntax.md -
ID sanitization, escaping, style definitions, and common pitfalls