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

Annotations already declare readOnlyHint=true, so safety is covered; the description adds real behavioral context beyond that: personal data is never shared across users, and it explains the semantic meaning of linkedAccount and the singleton isSelf flag. It stops short of describing pagination or ordering for the list mode.

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-loads the core purpose and the two modes in the first sentence, then adds field semantics. The trailing unit conventions (timestamps, distances, durations) are boilerplate that adds little for a tool with only an id parameter, so it is not fully waste-free.

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 carries return-value burden and does explain two key fields (linkedAccount, isSelf) plus the privacy boundary on birth date/passport. It does not enumerate the rest of the returned person attributes, leaving a modest gap for a read tool.

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%, so the baseline is 3, but the description adds meaning beyond the schema pattern: IDs are stated to be case-sensitive 6-character alphanumeric strings (the pattern alone does not convey case sensitivity), and it establishes unit/format conventions for the data returned.

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 ('Read the caller's private address book of people — crew and contacts') plus the two supported modes ('list them all, or get one by id'). It is clearly distinguishable from person_write and whoami without opening any schema.

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 listing-vs-get-by-id split gives implied mode selection guidance, but there is no explicit when-to-use versus siblings like person_write, trip_read, or whoami, and no exclusions or prerequisites. Adequate but leaves routing to inference.

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