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

Annotations already declare readOnlyHint, idempotentHint and openWorldHint=false, so the safety profile is covered; the description adds the non-obvious auth requirement ('needs the read permission'), which is genuinely useful context beyond the structured fields.

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?

Two compact sentences, with the core action and filter behavior front-loaded and the permission note trailing. Nothing is redundant.

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?

A single optional parameter, full schema coverage, an output schema covering return values, and annotations covering safety; the description adds scope, filter semantics and the permission prerequisite, so nothing an agent needs 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 100% and the schema already says 'Filter text; omit for the whole book', so baseline is 3; the description adds meaning by naming the searched fields (name/email/phone), which the schema does not specify.

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 ('Lists this organizer's saved address book') plus the optional narrowing dimension, which cleanly separates it from the sibling list_events and list_groups 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?

Gives clear context for the optional filter ('optionally filtered by a name/email/phone search'), implying use the unfiltered form to enumerate and the filtered form to find someone. No alternatives or exclusions are named, but no sibling competes for this read operation.

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