Validate phone number E.164 format, NANPA NPA-NXX carrier line type (mobile/landline/voip/toll_free), porting status, and TCPA DNC / serial litigator risk flags.
| Name | Required | Description | Default |
|---|---|---|---|
| phone | Yes | Phone number in E.164 or national format (e.g. +14155550199) | |
| country_code | No | US |
Changes observed during successful MCP inspections.
Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
With no annotations supplied, the description carries the full burden; it does convey that this is a read-only validation returning line type, porting status, and DNC risk flags, which is real behavioral context. It does not state permissions, rate limits, cost, data vintage, or what happens with non-US numbers, so the mutation-free/safety profile is only implied by the word "Validate".
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?
A single front-loaded sentence that leads with the action and then lists the specific signals returned; no filler. It is dense with domain jargon (NPA-NXX, serial litigator) but each phrase adds 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 read-only lookup with no output schema, enumerating the returned checks (format validity, line type, porting, DNC/litigator flags) is a reasonable proxy for return values, which is the main completeness need here. The gaps are behavioral rather than structural: no handling notes for invalid or international numbers and no clarification of the country_code parameter.
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 coverage is 50%: 'phone' is documented in the schema and the description reinforces the E.164 expectation, but 'country_code' is undocumented in both places. The NANPA reference hints that coverage is US-centric, but that is an inference rather than an explanation of the parameter's effect.
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?
Uses a specific verb ("Validate") plus resource ("phone number") and enumerates the exact checks performed: E.164 format, NPA-NXX line type, porting status, and TCPA DNC/litigator flags. This clearly separates it from generic validators, though it never names the close sibling validate_phone_tcpa to explain the distinction.
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 when-to-use or when-not-to-use guidance, no mention of prerequisites, and no reference to alternatives such as validate_phone_tcpa, lookup_fmcsa_carrier, or the sanctions screeners. The agent must infer from the term "TCPA DNC" that this is a compliance/litigation-risk check.
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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