skill-validator-omni

One command validates an agent skill or plugin against every standard that gates whether it installs and works across agents. The flagship check is Agent Plugins 1.0.0 (agent-plugins.org), the vendor-neutral spec for packaging Agent Skills and MCP servers into portable plugins, published by a Technical Steering Committee from Amazon, Cursor, Microsoft, OpenAI, and Vercel.

Other validators cover one spec. skills-ref checks only agentskills.io. Creation tools like skill-creator produce skills without certifying them. This tool checks the full set:

Agent Plugins 1.0.0: plugin.json manifest ($schema, name constraints, closed field set), skills/ layout, optional mcp.json
agentskills.io spec: name/dir rules, description length, compatibility <=500, allowed-tools
Anthropic best practices: third-person descriptions, progressive disclosure, bodies under 500 lines
Hermes in-repo standard: frontmatter fields, section structure, descriptions under 60 chars
OpenAgent skills.sh ecosystem: npx skills add discoverable layout, well-known index schema
Claude Code: plugin marketplace layout, plugin manifests, project .claude/skills/
OpenAI Codex: openai/skills frontmatter rules (closed field set), hyphen-case names, trigger-first descriptions, .agents/skills repo layout, no ancillary docs

Needs only Node >=18. No Python, no PyYAML.

Install into agents

The repo is packaged for every install path at once. Pick the one for your agent.

Claude Code

/plugin marketplace add adelpro/skill-validator-omni
/plugin install skill-validator-omni@adelpro-skill-validator-omni

Any agent via the skills.sh CLI

# preview what's in the repo
npx skills add adelpro/skill-validator-omni -l

# install into specific agents (claude-code, hermes-agent, codex, cursor, ...)
npx skills add adelpro/skill-validator-omni -a claude-code -a hermes-agent --copy -y

Hermes Agent

npx skills add adelpro/skill-validator-omni -s skill-validator-omni -a hermes-agent --copy -y

Agent Plugins clients

The repo root is itself an Agent Plugins package (plugin.json with the canonical $schema), so compatible clients can load skills/ and mcp.json directly.

The CLI itself (validation without installing the skill)

npx skill-validator-omni <dir>
npm i -g skill-validator-omni   # optional global install

Usage

# Human report. Exit 0 = all checks pass.
npx skill-validator-omni ./my-skill

# JSON report for CI pipelines.
npx skill-validator-omni ./my-skill --json

# Validate a whole repo. Discovers every skill under skills/ and agent dirs.
npx skill-validator-omni ./my-skills-repo

Choosing standards

By default every standard runs. To run only some:

npx skill-validator-omni ./my-skill --standard hermes          # one standard
npx skill-validator-omni ./my-skill -s hermes -s claude        # several (repeatable)
npx skill-validator-omni ./my-skill --all                      # every standard (the default)
npx skill-validator-omni --list-standards                      # valid names

General checks (skill discovery) always run, so a filtered run still answers "is this even a valid skill layout?". The JSON report records what was requested:

npx skill-validator-omni ./my-skill -s agentplugins --json | jq -r '.requested'

Unknown standard names exit with code 2 and print the valid names.

Per-standard scores

The report ends with a per-standard breakdown. Each standard gets its own pass/fail count, so you see where a skill falls short without reading every check:

$ npx skill-validator-omni ./my-skill
34/34 checks passed
Per standard:
  [PASS] agentskills.io: 6/6
  [PASS] Anthropic best practices: 3/3
  [PASS] Hermes in-repo: 12/12
  [PASS] OpenAgent skills.sh: 2/2
  [PASS] Claude Code: 4/4
  [PASS] Agent Plugins 1.0.0: 7/7
  [PASS] Codex (OpenAI): 12/12

In JSON mode the same breakdown lives in standards, one object per standard with passed, failed, total, and ok. Gate CI on a single standard:

npx skill-validator-omni . --json | jq -e '.standards["Agent Plugins 1.0.0"].ok'

Exit codes

Code	Meaning
0	All checks passed
1	One or more checks failed
2	Usage error / target unreadable

JSON output

{
  "tool": "skill-validator-omni",
  "version": "1.5.0",
  "target": "./my-skill",
  "passed": 27,
  "failed": 0,
  "total": 27,
  "ok": true,
  "standards": [
    { "name": "Agent Plugins 1.0.0", "passed": 7, "failed": 0, "total": 7, "ok": true, "checks": [] }
  ],
  "checks": [
    {
      "name": "spec: name == directory",
      "ok": true,
      "detail": "my-skill vs dir my-skill",
      "description": "Frontmatter name must equal the skill directory name. Installers (npx skills, agents) resolve a skill by directory, so a mismatch breaks discovery."
    }
  ]
}

Every check entry carries a description explaining what it verifies, so CI users and skill authors know what a failure means without reading the source.

What gets validated

Discovery follows the layouts the ecosystem actually installs from:

plugin.json at the repo root (Agent Plugins package) with the canonical $schema: https://agent-plugins.org/schemas/1.0.0/plugin.schema.json
SKILL.md at the repo root (single-skill repo)
skills/<name>/SKILL.md, walked up to 3 levels (skills/<category>/<skill>/SKILL.md)
agent dirs: .claude/skills/, .agents/skills/, .cursor/skills/, .codex/skills/, .gemini/skills/, .config/opencode/skills/
.well-known/agent-skills/index.json with $schema: https://schemas.agentskills.io/discovery/0.2.0/schema.json
.claude-plugin/marketplace.json + <plugin>/.claude-plugin/plugin.json + <plugin>/skills/
.agents/skills/ or .codex/skills/ (Codex repo-scoped auto-discovery), or an Agent Plugins plugin.json (Codex plugin distribution)

Every skill found in a repo gets the full check suite. A broken skill nested inside a big repo can't hide. Agent Plugins manifests are checked against the spec's closed field set and name constraints. The Codex standard mirrors openai/skills' own quick_validate.py (frontmatter limited to name/description/license/allowed-tools/metadata, hyphen-case names under 64 chars, no angle brackets in descriptions) plus the docs' trigger-first description guidance and .agents/skills repo layout.

Examples

# A compliant skill
$ npx skill-validator-omni ./my-skill
27/27 checks passed

# A broken one. Fails fast, tells you why.
$ npx skill-validator-omni ./my-skill
  [FAIL] spec: name == directory  ('My-Skill' vs dir 'my-skill')
  [FAIL] hermes: description <= 60  (73 chars)
1/27 checks passed

CI

npx skill-validator-omni . --json | jq -e '.ok'

Layout

skill-validator-omni/
├── bin/cli.js                  CLI entry
├── src/validate.js             the validator (library + standalone entry)
├── test/                       node --test suite
├── plugin.json                 Agent Plugins 1.0.0 manifest (self-validating)
├── .claude-plugin/             Claude Code marketplace + plugin manifests
└── skills/skill-validator-omni/     the Hermes skill (SKILL.md + scripts + references)

agent-plugins.org: the flagship standard
agentskills.io: the Agent Skills spec
skills-ref: validates the agentskills.io spec only
skill-creator: creates skills

License

MIT

adelpro/skill.validator