What is metaschema-constraints-authoring?

A guide to creating and changing Metaschema constraints, which are rules used to check whether documents contain valid data. It covers inline and separate rules, expressions, allowed values, patterns, uniqueness, references, and occurrence counts.

Use it to author constraints that restrict values, check conditions, validate formats, enforce required counts, create indexes, or verify unique and cross-referenced data.

It helps you choose and define the right validation rule without guessing the syntax or where it belongs.

metaschema-constraints-authoring — Skill by metaschema-framework

Install

Getting it into your agent

It runs from inside its repository, so the clone comes first — what it calls does not travel with the file alone.

Clone the repo

git clone --depth 1 https://github.com/metaschema-framework/claude-plugins

agentmods

npx agentmods add skills/metaschema-framework/claude-plugins/metaschema-constraints-authoring

Made for: Claude Code.

Or install metaschema, the plugin that ships this one along with the rest of its 4 skills.

Wrote this? Show the measurements

A badge with what this costs and how it scanned, read live from this page, so it follows the numbers instead of freezing them. Markdown for a README, HTML for a documentation site or a project page.

README.md

[![agentmods](https://agentmods.dev/badge/skills/metaschema-framework/claude-plugins/metaschema-constraints-authoring/github.svg)](https://agentmods.dev/skills/metaschema-framework/claude-plugins/metaschema-constraints-authoring)

Your own site

<a href="https://agentmods.dev/skills/metaschema-framework/claude-plugins/metaschema-constraints-authoring"><img src="https://agentmods.dev/badge/skills/metaschema-framework/claude-plugins/metaschema-constraints-authoring/github.svg" alt="Measured on agentmods" height="20"></a>

Or the 80×15 button, for a site that already has a row of RSS and ATOM ones. Only the verdict fits; the numbers stay here.

Your own site · 80×15

<a href="https://agentmods.dev/skills/metaschema-framework/claude-plugins/metaschema-constraints-authoring"><img src="https://agentmods.dev/badge/skills/metaschema-framework/claude-plugins/metaschema-constraints-authoring.svg" alt="Reviewed on agentmods" width="80" height="20"></a>

Per session 36 Skills are progressive disclosure: only the name and description are preloaded; the body loads when the skill is used.

When invoked 3,911 The whole file, excluding the scripts and references it only reads on demand.

Security scan A 0 findings. A grade says what 26 rules found in the file — not that it is safe.

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.

Model	Per session	Once invoked
Fable 5.1	$0.00036	$0.03911
Opus 5.5	$0.00014	$0.01564
Sonnet 5.5	$0.00007	$0.00782
Haiku 4.5	$0.00004	$0.00391

Measured 2mo ago against content hash d001380fb94c, method: parsed. Prices are Anthropic first-party input rates as of 2026-10-07, from the pricing page.

Security

Grade A, and why

metaschema-constraints-authoring 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 2mo 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.

plugins/metaschema/skills/metaschema-constraints-authoring/SKILL.md · 610 lines

How it starts

The opening of the file, as written. The whole thing — 610 lines — stays where its author put it; the contents beside it link to each section on GitHub.

Metaschema Constraints Authoring

This skill guides the creation of Metaschema constraints for validating document instances. Constraints can be defined inline within definitions or externally in constraint modules.

Constraint Types Overview

Constraint	Allowed On	Purpose
`allowed-values`	flag, field, assembly	Restrict values to enumerated set
`expect`	flag, field, assembly	Assert Metapath condition is true (fires when FALSE)
`report`	flag, field, assembly	Report when Metapath condition is true (fires when TRUE)
`matches`	flag, field, assembly	Validate against regex and/or datatype
`has-cardinality`	assembly only	Enforce occurrence counts
`index`	assembly only	Create named index with composite keys
`index-has-key`	flag, field, assembly	Validate cross-references against index
`is-unique`	assembly only	Ensure unique composite keys
`let`	all	Define reusable variables

Common Constraint Attributes

Attribute	Values	Default	Description
`id`	token	none	Constraint identifier
`level`	CRITICAL, ERROR, WARNING, INFORMATIONAL, DEBUG	ERROR	Violation severity
`target`	Metapath	`.` (flags/fields)	Node selection expression

Inline Constraints

Define constraints directly within flag, field, or assembly definitions.

YAML Syntax

- object-type: flag
  name: status
  as-type: token
  constraint:
    rules:
    - object-type: allowed-values
      enums:
      - value: active
        remark: The item is active.
      - value: inactive
        remark: The item is inactive.
      - value: pending
        remark: The item is pending approval.

XML Syntax

<define-flag name="status" as-type="token">
  <constraint>
    <allowed-values>
      <enum value="active">The item is active.</enum>
      <enum value="inactive">The item is inactive.</enum>
      <enum value="pending">The item is pending approval.</enum>
    </allowed-values>
  </constraint>
</define-flag>

Read the full file on GitHub · 610 lines

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.

2mo ago First seen · 610 lines · 36 tokens per session scan A d001380fb94c

Subscribe to this mod's changes

metaschema-constraints-authoring is a skill published in the GitHub repository metaschema-framework/claude-plugins (10 stars, last pushed 8mo ago), licensed CC0-1.0. It adds 36 tokens to every session and 3,911 once invoked, about $0.0001 per session on Opus 5.5. 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 2026-08-31.

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