[Extension]: Add T-Shirt Sizing Gate #5304

Extension ID

sizing

Extension Name

T-Shirt Sizing Gate

Version

0.1.2

Description

Adds T-Shirt sizing estimates (XS–XL) and an explicit human approval gate between planning and implementation, with SHA-256 checks to detect changes to approved planning artifacts.

Author

Maurizio Pinotti

Repository URL

https://github.com/mauriziopinotti/spec-kit-sizing

Download URL

https://github.com/mauriziopinotti/spec-kit-sizing/archive/refs/tags/v0.1.2.zip

License

MIT

Homepage (optional)

No response

Documentation URL (optional)

No response

Changelog URL (optional)

No response

Required Spec Kit Version

=1.3.0

Required Tools (optional)

- python (>=3.8)

Number of Commands

3

Number of Hooks (optional)

2

Tags

sizing, quality-gate, process

Key Features

• XS–XL implementation complexity estimation
• Automatic review after speckit.tasks
• Explicit human approval before implementation
• SHA-256 validation of planning artifacts
• Independent from Spec Kit core files

Testing Checklist

• Extension installs successfully via download URL
• All commands execute without errors
• Documentation is complete and accurate
• No security vulnerabilities identified
• Tested on at least one real project

Submission Requirements

• Valid extension.yml manifest included
• README.md with installation and usage instructions
• LICENSE file included
• GitHub release created with version tag
• All command files exist and are properly formatted
• Extension ID follows naming conventions (lowercase-with-hyphens)

Testing Details

Testing Details

Environment

• GitHub Spec Kit v1.3.1
• Python 3.11+
• GitHub Copilot
• macOS

Real-world testing

The extension has been manually tested across approximately 7–8 real-world features of varying sizes and complexity in active software development projects.

Testing focused on:

• T-Shirt size estimation (XS–XL) for changes of different scopes and complexity levels.
• Consistency between estimated complexity and expected implementation effort.
• Identification of affected components, potential risks, and complexity drivers.
• Integration with the standard Spec Kit workflow (specify → plan → tasks → implement).
• Human review and approval of complexity estimates before implementation.

Automated testing

The v0.1.2 release includes 8 passing automated regression tests.

Local extension installation and GitHub Copilot command generation have also been verified.

Compatibility and limitations

• Minimum supported Spec Kit version: 1.3.1.
• Compatibility with earlier Spec Kit versions has not been verified.
• Cross-platform compatibility has not been formally certified.
• The pre-implementation approval gate is enforced through coding-agent instructions and approval validation, rather than an independent runtime-level blocking mechanism.

Overall result

The extension has been successfully used in real development workflows to provide an additional human review checkpoint between planning and implementation, helping identify unexpected complexity and potential overengineering before coding begins.

Example Usage

**Example: Adding a new API endpoint**

1. Run the standard Spec Kit workflow:
   - `/speckit.specify`
   - `/speckit.plan`
   - `/speckit.tasks`

2. After task generation, the extension automatically evaluates the implementation scope.

3. Example assessment:

   **T-Shirt Size: S (Small)**
   - Estimated files: 3–5
   - Components: REST controller, service layer, unit tests
   - Database changes: None
   - Risk: Low
   - Confidence: High

4. Review the estimate. If it matches expectations, explicitly approve it using `/speckit-sizing-approve`.

5. Run `/speckit.implement`. The extension checks the approval before implementation proceeds.

6. If the approved planning artifacts have changed, the approval is invalidated and a new review is required.

The extension also supports manual estimation through `/speckit-sizing-estimate` without requiring modifications to Spec Kit's core commands.

Proposed Catalog Entry

{
  "id": "sizing",
  "name": "T-Shirt Sizing Gate",
  "description": "Estimate implementation complexity (XS–XL) and require explicit human approval before coding, with change detection for approved planning artifacts.",
  "author": "Maurizio Pinotti",
  "version": "0.1.2",
  "download_url": "https://github.com/mauriziopinotti/spec-kit-sizing/archive/refs/tags/v0.1.2.zip",
  "repository": "https://github.com/mauriziopinotti/spec-kit-sizing",
  "homepage": "https://github.com/mauriziopinotti/spec-kit-sizing",
  "documentation": "https://github.com/mauriziopinotti/spec-kit-sizing/blob/main/README.md",
  "changelog": "https://github.com/mauriziopinotti/spec-kit-sizing/blob/main/CHANGELOG.md",
  "license": "MIT",
  "category": "process",
  "effect": "read-write",
  "requires": {
    "speckit_version": ">=1.3.1",
    "tools": [
      {
        "name": "python3",
        "version": ">=3.11",
        "required": true
      }
    ]
  },
  "provides": {
    "commands": 3,
    "hooks": 2
  },
  "tags": [
    "sizing",
    "quality-gate",
    "process"
  ],
  "verified": false
}

Additional Context

No response