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

Annotations already declare readOnly/non-destructive, and the description adds real value beyond them: deleted and merged contacts are never returned, results are newest-first by default, and pagination is cursor-based with the last page lacking `nextCursor`. Return shape is described only at a high level (no field list), which keeps it from a 5.

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?

Front-loaded with the core action, then a bulleted per-parameter breakdown, then pagination rules. Every sentence carries distinct information with no repetition of the schema.

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 search tool with no output schema and no required parameters, it covers matching semantics, default behavior, exclusion rules, ordering, and the full pagination loop. Nothing an agent needs to call it correctly is missing.

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 only 40%, but the description compensates fully for the undocumented parameters: `email` is case-insensitive, `phone` matches regardless of formatting, `query` mirrors the Contacts screen search, and `cursor` must be the prior page's `nextCursor` with the same filter. Only `limit` is left to the schema, which already documents it.

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?

States a specific verb and resource ('Finds the user's contacts') plus the exact matching keys (email, phone, query). This clearly separates it from contact_read (single-contact lookup) and contact_change/create without needing to name them.

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?

Explicitly constrains usage: 'Give at most one of email, phone and query' and explains the no-argument behavior ('every contact is listed, newest first'). It doesn't route the agent to sibling tools like contact_read for direct ID lookups, so not a full 5.

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