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FabTally Utility Belt

by io.github.zvmzaretsky
OverviewDiscussionsAdmin

JSON-Schema (2020-12) validate + explain (paid $0.001)

jsonschema

PAID $0.001. Validate a value against a JSON Schema (draft 2020-12) and explain every error in plain English (which property, what was wrong, allowed values). Args: schema (object), data (any). Without payment returns the x402 challenge; pass x_payment to settle.

Tool call template

Replace each placeholder with a value matching the input schema. Only required parameters are included; add optional parameters as needed.

{
  "id": 1,
  "jsonrpc": "2.0",
  "method": "tools/call",
  "params": {
    "arguments": {
      "schema": "<schema>"
    },
    "name": "jsonschema"
  }
}

Input Schema

NameRequiredDescriptionDefault
dataNoThe value to validate against the schema.
schemaYesA JSON Schema (draft 2020-12) object.
x_paymentNox402 payment payload (base64) for this PAID tool. If supplied it is forwarded as the X-PAYMENT header to settle the $0.001 call and return the real result instead of a 402 challenge. Omit to get the price challenge first.

Schema Changelog

Changes observed during successful MCP inspections.

  1. First observed

TDQS

A4.4/5.0
Behavior5/5

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

With no annotations provided, the description carries the full burden. It discloses the payment requirement ($0.001), the challenge behavior ('Without payment returns the x402 challenge'), and the detail level of error explanations ('which property, what was wrong, allowed values'). This is transparent about cost, failure mode, and output quality.

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?

The description is a compact two-sentence structure that front-loads the paid nature and then states the core functionality. It avoids unnecessary words and every clause delivers useful information, including the appeal to pass x_payment.

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

Completeness4/5

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

The description covers the main workflow: validation, error explanation, payment challenge, and settlement. Since there is no output schema, it adequately describes return behavior (errors in plain English, challenge response). It falls slightly short of a 5 by not explicitly describing the successful validation result, but the overall context is sufficient for a simple tool.

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?

The schema description coverage is 100%, so each parameter already has a description. The tool description only lists the args ('schema (object), data (any)') without adding extra meaning beyond the schema. It does clarify x_payment's purpose, but that is already well-described in the schema. Thus, it meets the baseline for high schema coverage.

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 verb 'Validate' and the resource 'a JSON Schema (draft 2020-12)', with the added benefit of explaining errors in plain English. This distinguishes it from sibling utility tools like regex or convert. The purpose is specific and unambiguous.

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 implicitly indicates when to use the tool (for JSON Schema validation against draft 2020-12) and provides practical context about the payment prerequisite and x_payment parameter. It lacks explicit exclusions or named alternatives, but the usage context is clear enough for an agent to decide.

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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