Plugin Manifest Schema Notes

This document captures undocumented but enforced constraints of the Claude Code plugin manifest validator.

These rules are based on real installation failures, validator behavior, and comparison with known working plugins. They exist to prevent silent breakage and repeated regressions.

If you edit .claude-plugin/plugin.json, read this first.

Summary (Read This First)

The Claude plugin manifest validator is strict and opinionated. It enforces rules that are not fully documented in public schema references.

The most common failure mode is:

The manifest looks reasonable, but the validator rejects it with vague errors like agents: Invalid input

This document explains why.

Required Fields

version (MANDATORY)

The version field is required by the validator even if omitted from some examples.

If missing, installation may fail during marketplace install or CLI validation.

Example:

{
  "version": "1.1.0"
}

Field Shape Rules

The following fields must always be arrays:

• agents
• commands
• skills
• hooks (if present)

Even if there is only one entry, strings are not accepted.

Invalid

{
  "agents": "./agents"
}

Valid

{
  "agents": ["./agents/planner.md"]
}

This applies consistently across all component path fields.

Path Resolution Rules (Critical)

Agents MUST use explicit file paths

The validator does not accept directory paths for agents.

Even the following will fail:

{
  "agents": ["./agents/"]
}

Instead, you must enumerate agent files explicitly:

{
  "agents": [
    "./agents/planner.md",
    "./agents/architect.md",
    "./agents/code-reviewer.md"
  ]
}

This is the most common source of validation errors.

Commands and Skills

• commands and skills accept directory paths only when wrapped in arrays
• Explicit file paths are safest and most future-proof

Validator Behavior Notes

• claude plugin validate is stricter than some marketplace previews
• Validation may pass locally but fail during install if paths are ambiguous
• Errors are often generic (Invalid input) and do not indicate root cause
• Cross-platform installs (especially Windows) are less forgiving of path assumptions

Assume the validator is hostile and literal.

The hooks Field: DO NOT ADD

WARNING: CRITICAL: Do NOT add a "hooks" field to plugin.json. This is enforced by a regression test.

Why This Matters

Claude Code v2.1+ automatically loads hooks/hooks.json from any installed plugin by convention. If you also declare it in plugin.json, you get:

Duplicate hooks file detected: ./hooks/hooks.json resolves to already-loaded file.
The standard hooks/hooks.json is loaded automatically, so manifest.hooks should
only reference additional hook files.

The Flip-Flop History

This has caused repeated fix/revert cycles in this repo:

Root cause: Claude Code CLI changed behavior between versions:

• Pre-v2.1: Required explicit hooks declaration
• v2.1+: Auto-loads by convention, errors on duplicate

Current Rule (Enforced by Test)

The test plugin.json does NOT have explicit hooks declaration in tests/hooks/hooks.test.js prevents this from being reintroduced.

If you're adding additional hook files (not hooks/hooks.json), those CAN be declared. But the standard hooks/hooks.json must NOT be declared.

Known Anti-Patterns

These look correct but are rejected:

• String values instead of arrays
• Arrays of directories for agents
• Missing version
• Relying on inferred paths
• Assuming marketplace behavior matches local validation
• Adding "hooks": "./hooks/hooks.json" - auto-loaded by convention, causes duplicate error

Avoid cleverness. Be explicit.

Minimal Known-Good Example

{
  "version": "1.1.0",
  "agents": [
    "./agents/planner.md",
    "./agents/code-reviewer.md"
  ],
  "commands": ["./commands/"],
  "skills": ["./skills/"]
}

This structure has been validated against the Claude plugin validator.

Important: Notice there is NO "hooks" field. The hooks/hooks.json file is loaded automatically by convention. Adding it explicitly causes a duplicate error.

Recommendation for Contributors

Before submitting changes that touch plugin.json:

1. Use explicit file paths for agents
2. Ensure all component fields are arrays
3. Include a version
4. Run:

claude plugin validate .claude-plugin/plugin.json

If in doubt, choose verbosity over convenience.

Why This File Exists

This repository is widely forked and used as a reference implementation.

Documenting validator quirks here:

• Prevents repeated issues
• Reduces contributor frustration
• Preserves plugin stability as the ecosystem evolves

If the validator changes, update this document first.