Worth

Compare new, used, and resale

compare_prices

Read-onlyIdempotent

New, used, and resale prices for one named item. estimate_low and estimate_high carry a range already priced, or -1 when the title still needs a price.

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": {
      "title": "<title>"
    },
    "name": "compare_prices"
  }
}

Input Schema

Name	Required	Description
`grade`	No	Card grade such as PSA 9.
`title`	Yes	Item name to compare.
`category`	No	Category hint.
`condition`	No	Condition the user stated.
`estimate_low`	No	Low end from price_item. -1 when there is none.
`estimate_high`	No	High end from price_item. -1 when there is none.

Output Schema

Name	Required	Description	Default
`best`	Yes
`name`	Yes
`view`	Yes
`comps`	No
`links`	Yes
`priced`	Yes
`outcome`	Yes
`currency`	Yes
`headline`	Yes
`new_from`	Yes
`from_past`	No
`new_label`	Yes
`retailers`	No
`used_from`	Yes
`confidence`	Yes
`resale_low`	Yes
`used_label`	Yes
`resale_high`	Yes
`estimate_low`	Yes
`resale_label`	Yes
`estimate_high`	Yes
`confidence_label`	No

Schema Changelog

Changes observed during successful MCP inspections.

Changed2 schema fields changedOct 31, 2026

changedInput schema / properties / estimate_high / description

Previous value: -"High end from price_item. -1 if you do not have one."New value: +"High end from price_item. -1 when there is none."

changedInput schema / properties / estimate_low / description

Previous value: -"Low end from price_item. -1 if you do not have one."New value: +"Low end from price_item. -1 when there is none."

Changed2 schema fields changedOct 21, 2026
- addedOutput schema / properties / from_past
```
Added value: +{
+  "type": "boolean"
+}
```
- addedOutput schema / properties / retailers
```
Added value: +{
+  "type": "array"
+}
```
Changed2 schema fields changedOct 21, 2026
- addedOutput schema / properties / comps
```
Added value: +{
+  "type": "number"
+}
```
- addedOutput schema / properties / confidence_label
```
Added value: +{
+  "type": "string"
+}
```
First observedOct 21, 2026

TDQS

B3.4/5.0

Behavior3/5

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

Annotations already declare readOnlyHint, idempotentHint, and destructiveHint=false, so the safety profile is covered. The description adds useful behavioral detail about the -1 sentinel meaning the title still needs a price, but it does not describe return format, external pricing behavior beyond openWorldHint, or other operational traits.

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?

Two short sentences with no waste. The resource scope is front-loaded, and the sentinel behavior follows immediately. Every sentence earns its place.

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?

With a full input schema, an output schema, and rich annotations, the description supplies the key conceptual behavior around estimate fields and the -1 sentinel. It is largely complete, though it stops short of explaining how the tool fits relative to its sibling price_item.

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%, so the schema already documents all six parameters. The description adds clarification that estimate_low and estimate_high carry an already-priced range or -1 when pricing is still needed, but it does not add meaning for title, grade, category, or condition beyond the schema.

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

Purpose4/5

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

The description clearly states the resource and scope: new, used, and resale prices for one named item. However, it does not explicitly distinguish this tool from the sibling price_item, leaving the agent to infer that compare_prices provides comparison across price types.

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

Usage Guidelines2/5

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

There is no explicit guidance on when to use compare_prices rather than price_item or where_to_buy_or_sell. The mention of estimate_low/estimate_high coming 'from price_item' hints at a workflow relationship but does not clarify invocation conditions or exclusions.

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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