github-spec-kit/presets/ARCHITECTURE.md

Preset System Architecture

This document describes the internal architecture of the preset system — how template resolution, command registration, and catalog management work under the hood.

For usage instructions, see README.md.

Template Resolution

When Spec Kit needs a template (e.g. spec-template), the PresetResolver walks a priority stack and returns the first match:

flowchart TD
    A["resolve_template('spec-template')"] --> B{Override exists?}
    B -- Yes --> C[".specify/templates/overrides/spec-template.md"]
    B -- No --> D{Preset provides it?}
    D -- Yes --> E[".specify/presets/‹preset-id›/templates/spec-template.md"]
    D -- No --> F{Extension provides it?}
    F -- Yes --> G[".specify/extensions/‹ext-id›/templates/spec-template.md"]
    F -- No --> H[".specify/templates/spec-template.md"]

    E -- "multiple presets?" --> I["lowest priority number wins"]
    I --> E

    style C fill:#4caf50,color:#fff
    style E fill:#2196f3,color:#fff
    style G fill:#ff9800,color:#fff
    style H fill:#9e9e9e,color:#fff

Priority	Source	Path	Use case
1 (highest)	Override	.specify/templates/overrides/	One-off project-local tweaks
2	Preset	.specify/presets/<id>/templates/	Shareable, stackable customizations
3	Extension	.specify/extensions/<id>/templates/	Extension-provided templates
4 (lowest)	Core	.specify/templates/	Shipped defaults

When multiple presets are installed, they're sorted by their priority field (lower number = higher precedence). This is set via --priority on specify preset add.

The resolution is implemented three times to ensure consistency:

• Python: PresetResolver in src/specify_cli/presets.py
• Bash: resolve_template() in scripts/bash/common.sh
• PowerShell: Resolve-Template in scripts/powershell/common.ps1

Composition Strategies

Templates, commands, and scripts support a strategy field that controls how a preset's content is combined with lower-priority content instead of fully replacing it:

Strategy	Description	Templates	Commands	Scripts
replace (default)	Fully replaces lower-priority content	✓	✓	✓
prepend	Places content before lower-priority content (separated by a blank line)	✓	✓	—
append	Places content after lower-priority content (separated by a blank line)	✓	✓	—
wrap	Content contains {CORE_TEMPLATE} (templates/commands) or $CORE_SCRIPT (scripts) placeholder replaced with lower-priority content	✓	✓	✓

Composition is recursive — multiple composing presets chain. The PresetResolver.resolve_content() method walks the full priority stack bottom-up and applies each layer's strategy.

Content resolution functions for composition:

• Python: PresetResolver.resolve_content() in src/specify_cli/presets.py (templates, commands, and scripts)
• Bash: resolve_template_content() in scripts/bash/common.sh (templates only; command/script composition is handled by the Python resolver)
• PowerShell: Resolve-TemplateContent in scripts/powershell/common.ps1 (templates only; command/script composition is handled by the Python resolver)

Command Registration

When a preset is installed with type: "command" entries, the PresetManager registers them into all detected agent directories using the shared CommandRegistrar from src/specify_cli/agents.py.

flowchart TD
    A["specify preset add my-preset"] --> B{Preset has type: command?}
    B -- No --> Z["done (templates only)"]
    B -- Yes --> C{Extension command?}
    C -- "speckit.myext.cmd\n(3+ dot segments)" --> D{Extension installed?}
    D -- No --> E["skip (extension not active)"]
    D -- Yes --> F["register command"]
    C -- "speckit.specify\n(core command)" --> F
    F --> G["detect agent directories"]
    G --> H[".claude/commands/"]
    G --> I[".gemini/commands/"]
    G --> J[".github/agents/"]
    G --> K["... (17+ agents)"]
    H --> L["write .md (Markdown format)"]
    I --> M["write .toml (TOML format)"]
    J --> N["write .agent.md + .prompt.md"]

    style E fill:#ff5722,color:#fff
    style L fill:#4caf50,color:#fff
    style M fill:#4caf50,color:#fff
    style N fill:#4caf50,color:#fff

Extension safety check

Command names follow the pattern speckit.<ext-id>.<cmd-name>. When a command has 3+ dot segments, the system extracts the extension ID and checks if .specify/extensions/<ext-id>/ exists. If the extension isn't installed, the command is skipped — preventing orphan files referencing non-existent extensions.

Core commands (e.g. speckit.specify, with only 2 segments) are always registered.

Agent format rendering

The CommandRegistrar renders commands differently per agent:

Agent	Format	Extension	Arg placeholder
Claude, Cursor, opencode, Windsurf, etc.	Markdown	.md	$ARGUMENTS
Copilot	Markdown	.agent.md + .prompt.md	$ARGUMENTS
Gemini, Qwen, Tabnine	TOML	.toml	{{args}}

Cleanup on removal

When specify preset remove is called, the registered commands are read from the registry metadata and the corresponding files are deleted from each agent directory, including Copilot companion .prompt.md files.

Catalog System

flowchart TD
    A["specify preset search"] --> B["PresetCatalog.get_active_catalogs()"]
    B --> C{SPECKIT_PRESET_CATALOG_URL set?}
    C -- Yes --> D["single custom catalog"]
    C -- No --> E{.specify/preset-catalogs.yml exists?}
    E -- Yes --> F["project-level catalog stack"]
    E -- No --> G{"~/.specify/preset-catalogs.yml exists?"}
    G -- Yes --> H["user-level catalog stack"]
    G -- No --> I["built-in defaults"]
    I --> J["default (install allowed)"]
    I --> K["community (discovery only)"]

    style D fill:#ff9800,color:#fff
    style F fill:#2196f3,color:#fff
    style H fill:#2196f3,color:#fff
    style J fill:#4caf50,color:#fff
    style K fill:#9e9e9e,color:#fff

Catalogs are fetched with a 1-hour cache (per-URL, SHA256-hashed cache files). Each catalog entry has a priority (for merge ordering) and install_allowed flag.

Repository Layout

presets/
├── ARCHITECTURE.md                         # This file
├── PUBLISHING.md                           # Guide for submitting presets to the catalog
├── README.md                               # User guide
├── catalog.json                            # Official preset catalog
├── catalog.community.json                  # Community preset catalog
├── scaffold/                               # Scaffold for creating new presets
│   ├── preset.yml                          # Example manifest
│   ├── README.md                           # Guide for customizing the scaffold
│   ├── commands/
│   │   ├── speckit.specify.md              # Core command override example
│   │   └── speckit.myext.myextcmd.md       # Extension command override example
│   └── templates/
│       ├── spec-template.md                # Core template override example
│       └── myext-template.md               # Extension template override example
└── self-test/                              # Self-test preset (overrides all core templates)
    ├── preset.yml
    ├── commands/
    │   └── speckit.specify.md
    └── templates/
        ├── spec-template.md
        ├── plan-template.md
        ├── tasks-template.md
        ├── checklist-template.md
        ├── constitution-template.md
        └── agent-file-template.md

Module Structure

src/specify_cli/
├── agents.py       # CommandRegistrar — shared infrastructure for writing
│                    #   command files to agent directories
├── presets.py       # PresetManifest, PresetRegistry, PresetManager,
│                    #   PresetCatalog, PresetCatalogEntry, PresetResolver
└── __init__.py      # CLI commands: specify preset list/add/remove/search/
                     #   resolve/info, specify preset catalog list/add/remove