fetchgate

Get Purchase Info

get_purchase_info

Look up a product by id (from list_products) and explain exactly how to buy it: its price, and the x402 purchase flow step by step (the 402 challenge shape, the PAYMENT-SIGNATURE header, and the signed download URL you get back on success). Does not take payment itself — informational only, mirroring the pre-payment leg of GET /v1/buy/:id.

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": {
      "product_id": "<product_id>"
    },
    "name": "get_purchase_info"
  }
}

Input Schema

Name	Required	Description	Default
`product_id`	Yes	Product id, from list_products' `id` field.

Schema Changelog

Changes observed during successful MCP inspections.

First observedAug 22, 2026

TDQS

A4.2/5.0

Behavior4/5

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

No annotations are provided, so the description carries the behavioral disclosure burden. It clearly states that the tool is informational only, does not take payment, mirrors the pre-payment leg of the buy endpoint, and describes the success response shape. It omits edge-case behavior such as not-found handling, but the core behavior is transparent.

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 front-loaded with the main action and uses every sentence to add detail: where the id comes from, what the tool returns, the technical flow elements, and the no-payment constraint. Nothing is redundant.

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?

For a single-parameter informational tool with no output schema, it covers the input source, the exact output content, and the key limitation. It could mention error or missing-product behavior, but the essentials for invoking it correctly are all present.

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 description coverage is 100%, and the single product_id parameter is already well documented. The description adds useful context by referencing list_products as the source of the id, but it does not need to compensate for any schema gaps.

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 states a concrete operation: look up a product by id and explain its purchase process. It goes beyond a generic verb by specifying exact output content (price, x402 flow, PAYMENT-SIGNATURE header, signed download URL) and explicitly distinguishes itself as informational rather than payment-taking.

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?

It gives clear usage context: use it after getting an id from list_products, and it explicitly says it does not take payment. However, it does not explicitly name sibling alternatives or state when not to use them, so it falls just short of fully routable guidance.

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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