excalidraw

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

Create Operation

Compare Operation

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

Token Analysis (Why This Matters)

Real data from baseline testing:

Context pollution impact:

• Reading all 7 project diagrams: 67k tokens (33% of 200k budget)
• With delegation: ~2k tokens (isolated in subagents)
• Savings: 97% context budget preserved

Implementation Example

❌ BAD (Direct Read):

✅ GOOD (Subagent Delegation):

Why "Straightforward JSON" Doesn't Matter

Agents often rationalize: "The format is simple, I can just read it."

The problem isn't complexity - it's verbosity:

• Simple structure with 20+ properties per element
• Repetitive metadata (seed, version, nonce, roughness)
• Positioning data (x, y, width, height) not semantically useful
• Visual styling (strokeColor, opacity, fillStyle) irrelevant to content

Token cost comes from volume, not complexity.

Even "straightforward" JSON consumes 4k-22k tokens because:

• 79 elements × ~280 tokens/element = 22k tokens
• Most tokens are metadata noise
• Only text labels and relationships matter (~10% of content)

The Iron Law

Main agents NEVER read Excalidraw files. No exceptions.

Not for:

• "Quick checks"
• "Small files"
• "Understanding format"
• "One-time analysis"
• "Optimal efficiency"

Always delegate. Isolation is free via subagents.*