search_contacts_by_phone

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

With no annotations provided, the description carries the full burden. It adds a key behavioral trait: 'Phone matching ignores formatting' with examples. However, it does not mention read-only nature, response structure, or any limits. The return statement is vague ('key details'). Adequate but not thorough.

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 concise with four front-loaded sentences. Every sentence adds value: purpose, when to use, formatting behavior, fallback action. No redundant or unnecessary text.

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 simple 1-param tool with no output schema, the description covers the core: what it does, when to use, formatting behavior, return summary, and no-match handling. It is nearly complete, though it could mention if multiple matches are possible or ordering. 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?

Schema description coverage is 100%, so the schema already documents the parameter well. The description repeats the formatting behavior and adds examples of acceptable formats, which adds marginal practical value. Baseline 3 is 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 clearly states 'Look up a contact by phone number' with a specific verb+resource. It further specifies the use case as 'go-to tool for voice agent caller identification', which distinguishes it from sibling tools like search_contacts (presumably for other criteria) and get_contact (for ID).

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 explicitly tells when to use the tool: 'When a call comes in, use this tool with the caller's phone number'. It also provides post-action guidance: 'If no match is found, the caller is unknown and you should create a new contact.' It lacks explicit when-not-to-use, but the context and implied alternative (search_contacts) are clear.

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