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

Annotations only declare readOnlyHint=true; the description adds substantive behavior beyond that: accounts lacking the contacts scope are skipped and surfaced in `errors` with a reconnect hint, and it restates the read-only/no-write guarantee. Error-path disclosure is exactly the kind of context annotations cannot carry.

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?

Dense but front-loaded — purpose first, then usage routing, then error semantics, then read-only guarantee. Every clause carries operational weight; nothing is restated from the title or schema verbatim without added meaning.

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 compensates by naming the returned fields (name, primary email, full email list, source) and the error channel. An agent has everything needed to call it and interpret results without opening another 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: query matches name, partial name, or email; accounts defaults to all Contacts-enabled accounts and is resolvable via list_accounts; and matches are returned per account. This goes modestly beyond the schema text.

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?

Specific verb (search) + resource (Google Contacts) plus the exact scope: saved contacts and auto-collected 'other contacts' across all connected accounts. It is clearly distinguishable from siblings list_contacts, list_other_contacts, and get_contact_groups, which are enumeration rather than name-resolution 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?

Explicitly states the intent (resolve a person's name to an email before composing/sending), gives branch behavior for 0 matches (fall back to message history or ask the user) and multiple matches (ask the user), and routes to list_accounts for account labels. This is a full when/when-not/alternative treatment.

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