Parse and validate phone numbers, then format them into E.164, national, and international formats while identifying the country.
Parse and format a phone number into E.164, national, and international formats. Validates the number and identifies the country.
| Name | Required | Description | Default |
|---|---|---|---|
| phone | Yes | Phone number (e.g., "+1 (212) 555-1234") | |
| country_code | No | ISO 3166-1 alpha-2 country code (e.g., "US", "GB", "DE"). Default: "US" |
Changes observed during successful MCP inspections.
v1.4.2Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
The readOnlyHint annotation already declares this is a non-destructive operation. The description adds that it validates and identifies the country, but it does not disclose error handling behavior (e.g., what happens with invalid numbers) or any rate limits or special constraints. The description aligns with annotations but adds limited behavioral context beyond them.
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?
The description is a single, well-structured sentence that front-loads the primary action and outputs. There is no redundant information, and every phrase contributes to understanding the tool's capability.
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 no output schema, the description conveys the expected outputs (formats and country) but does not detail the return structure or error responses. Given the tool's moderate complexity and the read-only annotation, this is reasonably complete, though a mention of error handling would push it to 5.
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 input schema provides 100% coverage of both parameters with clear descriptions and a default for country_code. The description does not add additional parameter semantics beyond what the schema already provides, 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 clearly states the verb 'Parse and format' and the resource 'phone number', and specifies the output formats (E.164, national, international). It also adds validation and country identification, making the tool's purpose unambiguous and distinct from all sibling tools.
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 implicitly defines when to use the tool (when you need to format or validate a phone number) and there is no sibling that performs similar functionality. However, it does not explicitly state when not to use it or provide alternative tool references, so it falls short of a 5.
Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.