meta.yml Schema & Required Fields

ELI5

meta.yml is the shipping label on the prompt box: a few mandatory boxes (id, title, version, dates), some optional notes for the postman (tags, notes), and a description-shaped barcode that decides whether Anthropic’s skill scanner will even pick the box up.

Technical Deep Dive

Required vs. Optional

bin/eva:49 declares the seven REQUIRED_META keys; absence or blank value fails eva doctor:

Class Diagram

classDiagram
    class Meta {
      +id : string
      +title : string
      +summary : string
      +status : draft|tested|ready
      +version : string
      +created : date
      +updated : date
      +tags : string[]
      +model : string
      +description : string
      +triggers : string[]
      +not_for : string[]
      +inputs : Input[]
      +promotion : PromotionGates
      +notes : string
    }
    class Input { +name; +required }
    class PromotionGates { +min_uses; +require_eval }
    Meta --> "0..*" Input
    Meta --> PromotionGates

Cross-Validation

eva doctor (bin/eva:362-369) parses {{var}} placeholders out of prompt.xml and reconciles against meta.inputs:

• A {{var}} not declared in inputs → prompt.xml references undeclared var.
• A declared inputs[].required: true not referenced in prompt.xml → declared input '<name>' (required) not referenced.

description is additionally shape-checked by _check_skill_export_shape (bin/eva:287-326): forbids </>, caps at 1024 chars, warns if no “use when” trigger clause.

Key Terms

• REQUIRED_META → the seven-tuple at bin/eva:49 checked unconditionally by cmd_doctor.
• inputs[] → declared template variables; required: true means doctor must see {{name}} in prompt.xml.
• promotion — optional overrides for the lifecycle gates; see eva-003.

Q&A

Q: Which seven fields does eva doctor flag as required? A: id, title, summary, status, version, created, updated — REQUIRED_META at bin/eva:49.

Q: What is the maximum length of meta.description for skill export? A: 1024 characters (SKILL_DESCRIPTION_MAX, bin/eva:281); above that, doctor fails the prompt.

Q: Which two characters are forbidden inside meta.description? A: < and > — they break Anthropic skill frontmatter (bin/eva:304-305).

Examples

Minimal meta.yml that passes eva doctor:

id: hello
title: Greeter
summary: Generate a friendly greeting.
status: draft
version: 0.1.0
created: 2026-05-05
updated: 2026-05-05
inputs:
  - {name: name, required: true}