Schemastore

Fetch Schema

fetch_schema

Read-onlyIdempotent

Fetch a JSON Schema document by URL (must be hosted on json.schemastore.org).

Example tool call

This call uses example arguments supplied in the tool’s input schema.

{
  "id": 1,
  "jsonrpc": "2.0",
  "method": "tools/call",
  "params": {
    "arguments": {
      "url": "https://json.schemastore.org/package.json"
    },
    "name": "fetch_schema"
  }
}

Input Schema

Name	Required	Description	Default
`url`	Yes	e.g. https://json.schemastore.org/package.json

Output Schema

Name	Required	Description	Default
No arguments

Schema Changelog

Changes observed during successful MCP inspections.

Changed2 schema fields changedMay 22, 2026

addedInput schema / examples

Added value: +[
+  {
+    "url": "https://json.schemastore.org/package.json"
+  },
+  {
+    "url": "https://json.schemastore.org/tsconfig.json"
+  }
+]

changedOutput schema / (root)

Previous value: -nullNew value: +{
+  "description": "JSON Schema document (passthrough from SchemaStore)",
+  "type": "object"
+}

First observedMay 13, 2026

TDQS

A4.3/5.0

Behavior4/5

Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?

Annotations already indicate readOnly, idempotent, and non-destructive behavior. The description adds the important behavioral constraint about the allowed URL domain, which is beyond what annotations provide. No contradiction.

Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.

Conciseness5/5

Is the description appropriately sized, front-loaded, and free of redundancy?

Single, front-loaded sentence with no wasted words. Every part is essential for understanding the tool.

Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.

Completeness5/5

Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?

Given the presence of an output schema and annotations, the description is complete. It covers the key constraint and purpose without omission.

Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.

Parameters3/5

Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?

Schema coverage is 100% with examples. The description adds minimal value beyond the schema, simply restating that the URL is a fetch target. Baseline 3 is appropriate.

Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.

Purpose5/5

Does the description clearly state what the tool does and how it differs from similar tools?

The description clearly states the action ('Fetch') and resource ('JSON Schema document') with a specific constraint ('must be hosted on json.schemastore.org'). This distinguishes it from sibling tools like 'find_schema_for' and 'list_schemas'.

Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.

Usage Guidelines4/5

Does the description explain when to use this tool, when not to, or what alternatives exist?

The description provides a clear when-to-use constraint (URL must be on json.schemastore.org) but does not explicitly mention alternatives or when not to use this tool. However, the constraint itself guides the agent.

Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.

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