overlay-generator

name	overlay-generator
description	Generate client-specific overlay files (metadata, permissions, manifests) from a canonical SKILL.md source for different AI agent clients. Use when publishing a skill to multiple ecosystems (Copilot, OpenCode, Codex, Gemini CLI), converting between overlay formats, or validating overlay consistency. Do not use when creating skills for a single client only or when editing skill content (edit SKILL.md first, then regenerate overlays).
license	Apache-2.0
compatibility	{"clients":["openai-codex","gemini-cli","opencode","github-copilot"]}

Overlay Generator

Generates client-specific overlays from a canonical SKILL.md source. Each AI client has different metadata requirements — this skill produces the right format while keeping content authoritative in one place.

Architecture

SKILL.md (canonical source of truth)
    │
    ├── metadata.json      (Copilot overlay)
    ├── permissions.yaml   (OpenCode overlay)
    ├── openai.yaml        (Codex overlay)
    └── manifest.json      (Universal cross-client index)

Procedure

1. Parse SKILL.md frontmatter

Extract: name, description, license, compatibility.clients, and all metadata fields.

2. Generate overlays per target client

For each compatible client, generate the appropriate overlay format:

Copilot (metadata.json):

{
  "name": "<name>",
  "version": "1.0.0",
  "description": "<description>",
  "main": "SKILL.md",
  "license": "<license>"
}

OpenCode (permissions.yaml):

name: <name>
description: "<description>"
permissions:
  read: ["src/**/*", "tests/**/*", "docs/**/*"]
  write: ["src/**/*", "tests/**/*"]

Codex (openai.yaml):

name: <name>
description: "<description>"
schema_version: "1.0"
capabilities: [file_read, file_write, shell_execute]

3. Validate consistency

# All overlays must reference the same name and description
grep -h "name" metadata.json permissions.yaml openai.yaml 2>/dev/null | sort -u
# Validate JSON/YAML syntax
cat metadata.json | jq . 2>/dev/null

4. Batch generation (for skill libraries)

for skill_dir in */; do
  if [ -f "$skill_dir/SKILL.md" ]; then
    # Generate overlays for each skill
  fi
done

Output contract

Per skill:

skill-name/
├── SKILL.md           # Canonical source (unchanged)
├── metadata.json      # Copilot overlay (if compatible)
├── permissions.yaml   # OpenCode overlay (if compatible)
└── openai.yaml        # Codex overlay (if compatible)

At library root: skills-manifest.json indexing all skills and their overlays.

Failure handling

• Missing frontmatter field: Use sensible defaults, log warning
• Invalid YAML in frontmatter: Stop, report parse error with line number
• Client not in compatibility list: Skip that overlay, log skip
• Overlay already exists: Backup existing, regenerate, show diff for review

References

• Anthropic Skills format: https://github.com/anthropics/skills
• Overlay formats evolve with client releases — check client docs for current schema