yaml-schema

A skill for loading and checking agent.yml, a YAML configuration file that describes agents and how they connect. It defines typed models and validation rules before the configuration is compiled and run.

In plain words
What is it for?
Use it when defining the YAML schema, loading configuration, checking graph connections, validating tools and resolvers, or enforcing configuration security rules.
Why use it?
It prevents malformed, unsafe, or incomplete agent configurations from reaching the runtime, while reporting useful error locations.

Skill for Claude CodeCodex

Install

Getting it into your agent

One page per mod, every tool's command on it. A separate URL per tool would split the same page into five that compete with each other.

agentmods
npx agentmods add skills/extra-org/extra/yaml-schema
Any agent
npx skills add extra-org/extra --skill yaml-schema
Clone the repo
git clone --depth 1 https://github.com/extra-org/extra

Made for: Claude Code, Codex.

Per session 36 Skills are progressive disclosure: only the name and description are preloaded; the body loads when the skill is used.
When invoked 511 The whole file, excluding the scripts and references it only reads on demand.
Security scan A 0 findings. Scan, not verified.
Origin original No closer match found in the catalogue.
Token cost

What it costs to keep this loaded

Counted locally with the o200k_base tokenizer, which is exact for GPT models; Claude uses its own tokenizer and its counts differ. Treat this as one consistent yardstick across the catalogue rather than a bill. Prices are per million input tokens.

ModelPer sessionOnce invoked
Fable 5 $0.00036 $0.00511
Opus 5 $0.00018 $0.00255
Sonnet 5 $0.00007 $0.00102
Haiku 4.5 $0.00004 $0.00051

Measured 2d ago against content hash 6e52ec1c86fb, method: parsed. Prices are Anthropic first-party input rates as of 2026-08-30, from the pricing page.

Security

Grade A, and why

yaml-schema scanned grade A with 0 findings against 26 rules in 11 categories — prompt injection, anti-refusal, data exfiltration, privilege escalation, supply chain, agent snooping, system-prompt leakage, SSRF and excessive agency — measured 2d ago.

A static scan of the body, not an audit. Every finding is printed with the line that produced it so you can judge whether it matters here. A mod is markdown that instructs an agent; that is exactly why what it instructs is worth reading.

Nothing flagged

None of the 26 patterns this scan looks for appear in this file: no shell pipes, no recursive deletes, no credential paths, no hidden text, no instruction-override or anti-refusal phrasing, no agent-config snooping. That is not a guarantee, it is the absence of the things that are checkable.

.claude/skills/yaml-schema/SKILL.md · 64 lines

What it actually says

Skill: YAML Schema & Validation

When to use this skill

Use this when working on loading YAML configs, defining schema models, or validating the Agent Engine specification. Primary task: tasks/0002-yaml-schema-and-validation.md.

Files to read first

  • AGENTS.md
  • docs/YAML_SPEC.md
  • examples/agents.yml
  • examples/config.schema.json
  • docs/adr/0002-yaml-is-compiled-not-executed-directly.md

Architecture rules

  • YAML is declarative data, never code.
  • The spec has two halves: flat declarations and graph topology.
  • Validation must happen before compilation.
  • Runtime layers consume only validated/compiled models, never raw YAML dicts.
  • Secrets are never values in YAML.

Implementation rules

  • Define typed schema models in src/agentplatform/spec.
  • Validation belongs in src/agentplatform/validation.
  • Report all validation errors with useful locations.
  • Enforce: required system and graph; one graph root; graph ids exist in orchestrators or agents; no cycles; referenced resolvers/tools/MCPs exist; orchestrators have prompts.orchestrator; model overrides are complete; protected nodes require the access plugin at startup.
  • Keep schema/validation separate from the compiler.

Validation checklist

  • Schema models cover docs/YAML_SPEC.md.
  • examples/agents.yml validates successfully.
  • Dangling references, missing/multiple roots, and cycles fail clearly.
  • Unknown keys and hardcoded secrets are rejected.
  • Tests cover valid and invalid specs.
  • make check passes.

Common mistakes to avoid

  • Mixing validation with compilation or runtime logic.
  • Failing fast on the first error instead of collecting all errors.
  • Reintroducing the old definitions / hierarchy shape.
  • Letting unknown/typo'd keys pass silently.
Changes

What this file has done since we first saw it

Hashed on every crawl. A supply-chain change to an agent config is a question of when, not whether, so the history is kept rather than the latest state alone.

  1. 2d ago First seen · 64 lines · 36 tokens per session scan A 6e52ec1c86fb

Subscribe to this mod's changes

yaml-schema is a skill published in the GitHub repository extra-org/extra (108 stars, last pushed 4d ago), licensed MIT. It adds 36 tokens to every session and 511 once invoked, about $0.0002 per session on Opus 5. A static security scan graded it A with 0 findings. No closer match exists in the catalogue, so it is treated as the original; first seen 2026-08-30.

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