Context Compressor Skill

Core principle: Compress aggressively, decompress only when needed.

Compression Strategies

Strategy 1: Summary Mode

When: You've fully understood a file and may need to reference it later.

How:

File Summary: src/auth/login.ts

Purpose: Handles user login via email/password Key functions:

• handleLogin(req, res) → Validates credentials, returns JWT
• validateCredentials(email, password) → Checks against DB Dependencies: bcrypt, jose, database Tokens saved: ~400 (95 lines not reloaded)

Use instead of: Re-reading the full file

Strategy 2: Outline Mode

When: You need to understand a file's structure but not implementation details.

How:

Outline: src/services/payment.ts (127 lines)

• L1-15: Imports and types
• L17-35: PaymentService class
  • L20: constructor(config)
  • L25: processPayment(amount, method)
  • L45: refund(transactionId)
  • L67: getHistory(userId)
• L90-127: Helper functions

Tokens: ~50 vs ~500 for full file

Strategy 3: Diff-Only Mode

When: You've already seen a file and need to understand changes.

How:

Changes to: src/config.ts

Added:

• L45: TOKEN_BUDGET_THRESHOLD = 0.5
• L46: COMPRESSION_ENABLED = true

Modified:

• L12: MAX_CONTEXT → increased from 100000 to 150000

Use for: Reviewing modifications, understanding updates

Strategy 4: Reference Mode

When: You need to track a file without loading it.

How:

References

Cost: ~10 tokens vs ~200+ per file

Strategy 5: Progressive Disclosure

When: Unsure how much detail is needed.

Process:

• Start with outline (Level 1)

• If insufficient, load key functions (Level 2)

• If still stuck, load related code (Level 3)

• Full file only as last resort (Level 4)

L1: Outline → "I see handleLogin at L25" L2: Function → "handleLogin validates then calls createToken" L3: Related → "createToken uses jose.sign with HS256" L4: Full → Only for complex debugging

Compression Triggers

Automatic Compression Points

Trigger Action

After understanding a file Create summary

Switching tasks Compress previous context

Budget at 50% Aggressive outline mode

Budget at 70% Summary-only mode

End of wave Full compression pass

Decompression Protocol

When you need details from compressed context:

• Check summary first — Often sufficient

• Load specific section — If summary incomplete

• Full load as last resort — And re-compress after

Decompression Log

Compression Format Templates

Summary Template

📦 [filename]

Purpose: [one line] Key exports: [list] Dependencies: [list] Patterns: [notable patterns used] Watch for: [gotchas or edge cases]

Outline Template

📋 [filename] (N lines)

• L[start]-[end]: [section name]
  • L[n]: [key item]
  • L[n]: [key item]

Diff Template

Δ [filename]

+ [additions] - [removals] ~ [modifications]

Integration

Works with:

• token-budget — Triggers compression at thresholds

• context-fetch — Provides input for compression

• context-health-monitor — Monitors compression effectiveness

Anti-Patterns

❌ Keeping full files in mental context — Compress after understanding ❌ Re-reading instead of referencing — Use summaries ❌ Loading full file for one function — Use outline + target ❌ Skipping compression "to save time" — Costs more later

Part of GSD v1.6 Token Optimization. See docs/token-optimization-guide.md for examples.