Build a Claude Code Plugin and Complete the Production Capstone

Quick answer

A Claude Code plugin is a self-contained directory that packages reusable capabilities for distribution. Start with one skill, add only necessary agents/hooks/MCP configuration, test locally with --plugin-dir, inspect namespacing and permissions, then publish through a reviewed marketplace. Your capstone proves mastery by using this extension stack to ship a real feature with tests, security review, documentation, and rollback.

Use the current plugin creation guide and plugin reference as the source of truth.

Minimal plugin structure

release-guardian/
├── .claude-plugin/
│   └── plugin.json
├── skills/
│   └── release-check/
│       └── SKILL.md
├── agents/
│   └── migration-reviewer.md
├── hooks/
│   └── hooks.json
└── README.md

Illustrative manifest:

{
  "name": "release-guardian",
  "description": "Repeatable release verification and migration review",
  "version": "0.1.0",
  "author": { "name": "Your Team" }
}

Validate exact fields against current docs. Do not add components merely to make the plugin look complete.

Develop locally

Run Claude Code with the local plugin directory using the documented --plugin-dir workflow. Test:

• Discovery and namespaced invocation.
• Positive and negative skill activation.
• Hook success, failure, timeout, and malformed input.
• Subagent tool restrictions.
• Behavior with missing dependencies.
• Conflict with project-local commands or other plugins.
• Installation on a clean test account/workspace.

Review every bundled script and network destination. A plugin is executable supply-chain material.

Capstone: ship resilient webhook processing

Build a webhook endpoint that receives payment events and satisfies:

• Signature verification before parsing trusted fields.
• Idempotent handling of duplicate delivery.
• Durable event state and retry-safe processing.
• Constant safe response behavior for rejected requests.
• Structured logs without secrets or payment data.
• Unit, integration, and failure-path tests.
• Migration and rollback documentation.
• No new dependency without explicit justification.

Phase 1: explore

Use read-only mode to map the existing HTTP, persistence, and job-processing architecture. Use Context7 only for version-specific framework or SDK APIs. Produce an evidence map and unresolved decisions.

Phase 2: design

Use a structured planning workflow such as Superpowers. Define the trust boundary, idempotency key, transaction boundary, retry behavior, observability, and rollback. Use Ponytail to challenge unnecessary components.

Phase 3: implement

Create a failing test for invalid signatures, duplicate events, and partial processing. Implement vertical slices. Keep permissions narrow. Delegate independent security review to a read-only subagent.

Phase 4: verify

Run focused tests, the nearest integration suite, type/static checks, build, and an end-to-end replay with synthetic events. Inspect git diff, unexpected files, dependency changes, logs, and migration reversibility.

Phase 5: hand off

Produce:

• Root problem and accepted design.
• Changed files and public behavior.
• Verification commands with results.
• Security and privacy review.
• Deployment order and rollback.
• Monitoring signals and alert thresholds.
• Remaining risks and owners.

Graduation rubric

You have mastered the course when another engineer can reproduce your result from the repository and handoff, every claim maps to evidence, the automation has least privilege, failures are recoverable, and the solution is no larger than the requirements demand.

FAQ

Do plugins require a marketplace?

No. You can load local plugins during development. A marketplace makes installation and version distribution easier.

What should my first plugin contain?

One high-value skill with excellent documentation and tests. Add hooks, agents, or MCP only when the workflow genuinely requires them.

What is the difference between finishing and proving completion?

Finishing means code was written. Proving completion means acceptance criteria, tests, security, integration, and operational evidence all support the result.