mpp_phone_validatorValidate a phone number and get carrier and location details using MPP (Machine Payments Protocol). Pay-per-request, no API key required.
| Name | Required | Description | Default |
|---|---|---|---|
| phone | Yes | The phone number to validate in E.164 format |
| Name | Required | Description | Default |
|---|---|---|---|
| data | 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": {
+ "data": {}
+ },
+ "required": [
+ "data"
+ ],
+ "type": "object"
+}Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
Annotations already declare readOnlyHint and openWorldHint, so the description does not need to repeat safety behavior. It adds value by disclosing that the operation is pay-per-request and requires no API key, which is important operational context not captured by 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 concise sentences front-load the core action and result, then add the commercial/auth caveat. There is no filler or repetition of schema information.
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?
For a one-parameter read-only tool with an output schema and safety annotations, the description covers the essential context: what it validates, what it returns, the protocol, cost model, and auth requirement. It only lacks explicit sibling differentiation, which is a minor gap.
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?
The schema has 100% coverage of the single phone parameter, including format, pattern, and E.164 requirement. The description adds no parameter-level detail, so the baseline score of 3 applies.
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 specific action ('Validate a phone number'), a concrete result ('get carrier and location details'), and identifies the distinguishing protocol ('using MPP'), which differentiates it from the plain phone_validator sibling. The purpose is immediately clear.
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?
The description provides useful contextual cues — pay-per-request and no API key required — which imply when this variant might be preferred. However, it never explicitly states when to use this tool instead of phone_validator or mpp_phone_finder, nor gives any 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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