Context Descriptor Creation

Create rules that define exactly what context is needed for a task—whether for a sub-agent or a chat conversation.

Two Usage Modes

This skill works in two environments:

The rule format is identical—only the commands differ.

Why This Matters

When providing code context (to a sub-agent or yourself), curation is essential:

• •Too much: Full codebase overwhelms the context window (thousands of files, millions of tokens)
• •Too little: Missing information to complete the task
• •Wrong focus: Irrelevant code obscures what matters

Rules solve this by describing: which files to include fully, which to excerpt (signatures/structure only), and what to exclude entirely.

The Core Workflow

1. Understand the task
2. Explore the codebase (outlines, file reads)
3. Create a rule file
4. Validate the rule
5. Iterate until context is focused and complete
6. Generate and use the context

CLI vs MCP Commands

Rule Basics

Rules are YAML frontmatter + markdown, saved to .llm-context/rules/:

---
description: Refactor authentication to use JWT
compose:
  filters: [lc/flt-base]        # What to exclude
  excerpters: [lc/exc-base]     # How to excerpt
also-include:
  full-files:                   # Complete content
    - "/src/auth/**"
  excerpted-files:              # Structure/signatures only
    - "/src/api/routes/**"
---
## Task Context
The auth module needs migration from sessions to JWT tokens.
Focus on the middleware integration points.

Save as: .llm-context/rules/tmp-prm-auth-jwt.md

Two Categories of Files

Full files (5-15 typical):

• •Files to be modified
• •Small configs
• •Critical integration points

Excerpted files (10-30 typical):

• •Related modules (need structure, not every line)
• •Large files (only signatures/definitions)
• •Dependencies and callers

Excerpting uses tree-sitter to extract function/class definitions, reducing a 500-line file to ~50 lines of signatures.

Always Filter First

Without filters, you get thousands of files: build artifacts, node_modules, pycache, logs, etc.

compose:
  filters: [lc/flt-base]  # Standard exclusions (binaries, logs, caches)

Check if the project has custom filters (e.g., flt-repo-base) and compose them:

compose:
  filters: [flt-repo-base, lc/flt-base]

Then use also-include to add back specific files you need.

Validating Your Rule

Use the preview command/tool to see what a rule selects:

CLI: lc-preview tmp-prm-auth-jwt MCP: lc_preview tool with rule name

Rule: tmp-prm-auth-jwt
Composes: flt-repo-base → lc/flt-base

Full files (8):              12,400 bytes
  src/auth/handler.py         3,200 bytes
  src/auth/middleware.py      2,800 bytes
  ...

Excerpted files (15):         8,200 bytes (of 45,000)
  src/api/routes/user.py        420 bytes (of 2,800)
  src/api/routes/admin.py       380 bytes (of 3,100)
  ...

Total: 23 files, 20,600 bytes (~5k tokens)

This feedback lets you iterate:

• •Too large? Move files from full to excerpted, add exclusions
• •Missing something? Adjust patterns in also-include
• •Wrong files? Check your filter composition

Path Format

In rule patterns, paths start with /, relative to project root:

# Correct patterns in rules
- "/src/auth/**"
- "/config/settings.yaml"
- "**/*.py"

# Wrong
- "src/auth/**"           # Missing leading /
- "/src/"                 # Directory, not file pattern

Note: In generated context and preview output, paths include the project directory name as a prefix (e.g., /{project-name}/src/auth/handler.py). This enables multi-project context composition—combining files from multiple projects without path conflicts.

Sizing Guidelines

Aim for the smallest context that includes everything needed.

Quick Reference

Minimal context (start here for small tasks):

compose:
  filters: [lc/flt-no-files]   # Exclude everything
  excerpters: [lc/exc-base]
also-include:
  full-files:
    - "/specific/file.py"

Standard task:

compose:
  filters: [lc/flt-base]
  excerpters: [lc/exc-base]
also-include:
  full-files:
    - "/<modify>/**"
  excerpted-files:
    - "/<context>/**"

With project filters:

compose:
  filters: [flt-repo-base]  # Project-specific, composes lc/flt-base
  excerpters: [lc/exc-base]

Command Reference

CLI Commands (Agentic Harness)

MCP Tools (Chat Harness)

Note: In chat mode, use lc_outlines with a rule name to generate context, then lc_missing to retrieve full content for specific files as needed.

File Naming

• •prm-<name>.md - Permanent prompt rules
• •flt-<name>.md - Reusable filter rules
• •tmp-prm-<name>.md - Temporary task rules (delete after use)

Detailed syntax: SYNTAX.md Common patterns: PATTERNS.md Examples: EXAMPLES.md Troubleshooting: TROUBLESHOOTING.md