phone_lookup

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

Annotations already provide readOnlyHint=true, destructiveHint=false, idempotentHint=true, openWorldHint=true. The description adds crucial behavioral context: it explains the carrier omission behavior (when libphonenumber has no mapping) and instructs to always read carrier_status. This goes beyond what annotations convey, providing detailed transparency.

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 moderately long but every sentence adds value: purpose, usage, format, rate limits, return fields, and a critical behavioral note on carrier. It is well-structured with front-loaded purpose. Could be slightly tighter but remains efficient.

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?

Given the tool's low complexity (single parameter, rich annotations, output schema exists), the description is complete. It covers validation purpose, input requirements, output fields, rate limits, and a nuanced behavioral detail about carrier status that compensates for any ambiguity.

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 100% with one parameter. The description adds value beyond the schema by providing detailed format requirements (E.164, no spaces/dashes, examples for multiple countries) and explicitly listing wrong formats. This helps the agent format the input correctly.

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 it validates and analyzes phone numbers, listing specific fields (country, region, carrier, line type, timezone, formatted versions) and explicitly says it is used to verify legitimacy and detect fraud. It distinguishes itself from sibling tools by mentioning companion OSINT tools (username_lookup, email_disposable).

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 clear when-to-use guidance ('verify phone legitimacy and detect fraud risks') and a prerequisite (E.164 format). Rate limits are given (30/hr free, 500/hr Pro). It does not explicitly state when not to use or full alternatives, but the mention of companion tools provides some differentiation.

Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.