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Official specification and Claude Code plugin for YMD (YAML + Markdown + Jinja2) and PMD (Prompt Markdown + Jinja2) formats —
enabling structured, modular, and reusable AI prompts.
What are YMD and PMD?
YMD and PMD are file formats designed for prompt engineering that combine the best of YAML, Markdown, and Jinja2 templating.
This repository serves a triple purpose:
Format Specification: Official documentation of YMD and PMD formats for humans and LLMs
Claude Code Plugin: Tools for authoring, validating, and composing YMD/PMD files
Reference Implementation: Examples and patterns for structured prompts
.ymd files are complete prompt definitions with metadata and customizable sections.
Structure:
# Metadata (YAML)
meta:
id: pr_description_generator
kind: gh_pr
version: 0.1.0
title: Generate GitHub Pull Request Description
# Sections (Markdown + Jinja2)
system: |
You are a **senior maintainer** writing reviewer-friendly PR descriptions.
{% include "gh_pr/system_goals.pmd" %}
instructions: |
{% include "gh_pr/sections.pmd" %}
expected_output: |
{% include "gh_pr/example.pmd" %}
user: |
Context and diff:
```diff
{{ diff }}
**Key features**:
- **YAML metadata grouped under `meta:`**: `id`, `kind`, `version`, `title`
- **Customizable sections**: Standard (`system`, `instructions`, `user`) or custom (`context`, `constraints`)
- **Markdown content**: Rich formatting in block scalars (`|`)
- **Jinja2 templating**: Variables `{{ }}`, includes `{% %}`, control flow
- **PMD composition**: Include reusable components
### PMD: Prompt Components (Building Blocks)
`.pmd` files are **reusable Markdown blocks** for composition.
**Structure**:
```markdown
<!-- Pure Markdown + Jinja2 (no YAML) -->
You are a **{{ role_type }}** with expertise in:
- {{ primary_language }} development
- {{ domain }} best practices
{% include "../shared/code_principles.pmd" %}
Key features:
No YAML: Pure Markdown + Jinja2
Reusable: Shared across multiple YMD files
Composable: PMDs can include other PMDs recursively
Modular: Leaf components or composite components
Composition Patterns
YMD Orchestrates PMDs
YMD files are orchestrators that compose PMD components:
GitHub PR YMD (orchestrator)
├─ system section
│ └─ includes roles/maintainer.pmd
│ └─ includes shared/principles.pmd
├─ instructions section
│ ├─ includes tasks/pr_analysis.pmd
│ └─ includes checklists/quality.pmd
└─ user section
└─ includes formats/diff_context.pmd
PMDs Compose Recursively
PMD files can include other PMDs:
<!-- roles/senior_dev.pmd (composite) -->
You are a senior software engineer.
{% include "../shared/code_principles.pmd" %}
{% include "../shared/communication_style.pmd" %}
Usage
As a Format Specification
Use YMD/PMD to structure your AI prompts:
Create reusable PMD components:
roles/expert.pmd - Role definitions
checklists/security.pmd - Verification lists
formats/json_response.pmd - Output formats
Compose YMD manifests:
code_review.ymd - Includes expert role + security checklist
api_design.ymd - Includes expert role + json_response format
Benefit from modularity:
Update expert.pmd once → affects all YMDs that include it
Test PMDs independently with different variables
Version control individual components
As a Claude Code Plugin
Once installed, you can use YMD/PMD tools in three ways:
Option 1: Slash Commands (Recommended for Sessions)
Load YMD/PMD context for your current session:
/load-ymd-context
Available Commands:
/load-ymd-context - Load complete YMD/PMD format context
/create-ymd-manifest - Create new YMD file with scaffolding
/create-pmd-partial - Create new PMD component
/validate-composition - Validate YMD→PMD include chains
Option 2: Global CLAUDE.md (Automatic)
Reference in your ~/.claude/CLAUDE.md for automatic loading:
# YMD/PMD Format Support
@~/.claude/ymd-spec/context/format-guidelines.md
ymd-validator - Validates format and include chains
Format Specifications
YMD Format
File extension: .ymd or .yamd
Required metadata:
meta:
id: unique_identifier
kind: prompt_type
version: semver
title: Human-readable title
Standard sections (common patterns):
system - Role/persona definition
instructions - Step-by-step tasks
expected_output - Output format specification
developer - Implementation notes
user - User input template
Custom sections:
Any valid YAML key name
Same syntax: section_name: |
Same Markdown + Jinja2 support
Jinja2 features:
Variables: {{ variable_name }}
Includes: {% include "path.pmd" %}
Control flow: {% if %}, {% for %}
Comments: {# comment #}
PMD Format
File extension: .pmd
Structure:
Pure Markdown + Jinja2
No YAML metadata
Patterns:
Leaf PMDs: No includes, pure content
Composite PMDs: Include other PMDs recursively
Jinja2 features:
Same as YMD (variables, includes, control flow)
Examples
Simple YMD with Standard Sections
meta:
id: code_reviewer
kind: code_analysis
version: 1.0.0
title: Code Review Assistant
system: |
You are a code review specialist.
instructions: |
1. Analyze code quality
2. Check for security issues
3. Suggest improvements
user: |
Review this code:
```{{ language }}
{{ code }}
### YMD with Custom Sections
```yaml
meta:
id: api_designer
kind: api_design
version: 1.0.0
title: API Design Assistant
system: |
You are an API design expert.
context: |
This API will be used by {{ target_audience }}.
constraints: |
- RESTful principles
- JSON responses only
- Maximum response time: {{ max_response_time }}ms
user: |
Design an API for: {{ requirement }}
Leaf PMD (No Includes)
<!-- roles/expert.pmd -->
You are an expert in **{{ domain }}** with {{ years_experience }}+ years of experience.
Composite PMD (With Includes)
<!-- roles/senior_dev.pmd -->
You are a senior software engineer specializing in {{ primary_language }}.
{% include "../shared/code_principles.pmd" %}
{% include "../shared/communication_style.pmd" %}
Why YMD/PMD?
Benefits
✅ Modularity: Break large prompts into reusable components
✅ Reusability: Share PMDs across multiple YMD files
✅ Maintainability: Update PMD once, affects all consumers
✅ Versioning: Track changes to individual components
✅ Testability: Test PMDs independently with different variables
✅ Collaboration: Team members work on different PMDs simultaneously
✅ Customization: Sections are fully customizable, not limited to standard set
Comparison with Alternatives
Approach
Modularity
Type Safety
Templating
Customization
Plain Text
❌ No
❌ No
❌ No
✅ Yes
Markdown
⚠️ Limited
❌ No
❌ No
✅ Yes
YAML
⚠️ Limited
✅ Yes
❌ No
✅ Yes
YMD/PMD
✅ Yes
✅ Yes
✅ Yes
✅ Yes
Related Projects
vscode-ymd: VSCode extension for YMD/PMD syntax highlighting and navigation
