cost.estimateFREE read-only cost estimate. This tool never creates checkout, reserves funds, or contacts a facilitator.
| Name | Required | Description | Default |
|---|---|---|---|
| item_id | Yes | Public offer or paid capability identifier returned by offers.list. |
| Name | Required | Description | Default |
|---|---|---|---|
| cost | No | ||
| found | Yes | ||
| item_id | Yes | ||
| cost_state | Yes | ||
| payment_started | No | ||
| payment_required | Yes |
Changes observed during successful MCP inspections.
Output schema / (root)Previous value: -nullNew value: +{
+ "$schema": "http://json-schema.org/draft-07/schema#",
+ "additionalProperties": false,
+ "properties": {
+ "cost": {
+ "anyOf": [
+ {
+ "additionalProperties": true,
+ "properties": {},
+ "type": "object"
+ },
+ {
+ "type": "null"
+ }
+ ]
+ },
+ "cost_state": {
+ "type": "string"
+ },
+ "found": {
+ "type": "boolean"
+ },
+ "item_id": {
+ "type": "string"
+ },
+ "payment_required": {
+ "type": "boolean"
+ },
+ "payment_started": {
+ "type": "boolean"
+ }
+ },
+ "required": [
+ "item_id",
+ "found",
+ "cost_state",
+ "payment_required"
+ ],
+ "type": "object"
+}Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
Annotations already declare readOnlyHint=true, destructiveHint=false, and openWorldHint=false. The description adds that the tool is free and explicitly never creates checkout, reserves funds, or contacts a facilitator, which is useful behavioral context beyond the annotations.
Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.
Is the description appropriately sized, front-loaded, and free of redundancy?
Two sentences are efficiently used: the first front-loads the key qualifiers 'FREE read-only', and the second lists explicit negative side effects. No wasted words, and the most important information comes first.
Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.
Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?
With a rich output schema and annotations, the description provides adequate safety and cost information. However, it omits when to choose this tool over quote-related siblings, leaving a minor gap for agent selection.
Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.
Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?
Schema description coverage is 100%, so the single parameter item_id is fully documented in the schema. The description adds no additional parameter meaning, making the baseline score of 3 appropriate.
Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.
Does the description clearly state what the tool does and how it differs from similar tools?
The description states a verb and resource (cost estimate) but essentially restates the tool name; it does not explain what is being estimated or differentiate from siblings like commerce.quote. The added 'FREE read-only' is behavioral context, not purpose clarification.
Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.
Does the description explain when to use this tool, when not to, or what alternatives exist?
No guidance is given on when to use this tool versus alternatives such as commerce.quote or offers.list. The description only offers negative constraints about what the tool does not do, leaving the agent to infer appropriate usage.
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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