Excalidraw Subagent Delegation

Overview

Core principle: Main agents NEVER read Excalidraw files directly. Always delegate to subagents to isolate context consumption.

Excalidraw files are JSON with high token cost but low information density. Single files range from 4k-22k tokens (largest can exceed read tool limits). Reading multiple diagrams quickly exhausts context budget (7 files = 67k tokens = 33% of budget).

The Problem

Excalidraw JSON structure:

• Each shape has 20+ properties (x, y, width, height, strokeColor, seed, version, etc.)
• Most properties are visual metadata (positioning, styling, roughness)
• Actual content: text labels and element relationships (<10% of file)
• Signal-to-noise ratio is extremely low

Example: 14-element diagram = 596 lines, 16K, ~4k tokens. 79-element diagram = 2,916 lines, 88K, ~22k tokens (exceeds read limit).

When to Use

Trigger on ANY of these:

• File path contains .excalidraw or .excalidraw.json
• User requests: "explain/update/create diagram", "show architecture", "visualize flow"
• User mentions: "flowchart", "architecture diagram", "Excalidraw file"
• Architecture/design documentation tasks involving visual artifacts

Use delegation even for:

• "Small" files (smallest is 4k tokens - still significant)
• "Quick checks" (checking component names still loads full JSON)
• Single file operations (isolation prevents context pollution)
• Modifications (don't need full format understanding in main context)

Delegation Pattern

Main Agent Responsibilities

NEVER:

• ❌ Use Read tool on *.excalidraw files
• ❌ Parse Excalidraw JSON in main context
• ❌ Load multiple diagrams for comparison
• ❌ Inspect file to "understand the format"

ALWAYS:

• ✅ Delegate ALL Excalidraw operations to subagents
• ✅ Provide clear task description to subagent
• ✅ Request text-only summaries (not raw JSON)
• ✅ Keep diagram analysis isolated from main work

Subagent Task Templates

Read/Understand Operation

Task: Extract and explain the components in [file.excalidraw.json]

Approach:
1. Read the Excalidraw JSON
2. Extract only text elements (ignore positioning/styling)
3. Identify relationships between components
4. Summarize architecture/flow

Return:
- List of components/services with descriptions
- Connection/dependency relationships
- Key insights about the architecture
- DO NOT return raw JSON or verbose element details

Modify Operation

Task: Add [component] to [file.excalidraw.json], connected to [existing-component]

Approach:
1. Read file to identify existing elements
2. Find [existing-component] and its position
3. Create new element JSON for [component]
4. Add arrow elements for connections
5. Write updated file

Return:
- Confirmation of changes made
- Position of new element
- IDs of created elements

Create Operation

Task: Create new Excalidraw diagram showing [description]

Approach:
1. Design layout for [number] components
2. Create rectangle elements with text labels
3. Add arrows showing relationships
4. Use consistent styling (colors, fonts)
5. Write to [file.excalidraw.json]

Return:
- Confirmation of file created
- Summary of components included
- File location

Compare Operation

Task: Compare architecture approaches in [file1] vs [file2]

Approach:
1. Read both files
2. Extract text labels from each
3. Identify structural differences
4. Compare component relationships

Return:
- Key differences in architecture
- Components unique to each approach
- Relationship/flow differences
- DO NOT return full element details from both files

Common Rationalizations (STOP and Delegate Instead)

Red Flags - STOP and Delegate

Catch yourself about to:

• Use Read tool on .excalidraw file
• "Quickly check" what components exist
• "Understand the structure" before modifying
• Load file to "see what's there"
• Compare multiple diagrams side-by-side
• Parse JSON to "extract just the text"

All of these mean: Use Task tool with subagent instead.

Quick Reference

| Operation | Main Agent Action | Subagent Returns | |---

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