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

The readOnlyHint annotation already establishes this is a safe read. The description adds the returned field set (names, emails, phones, organizations), which is useful context, but says nothing about ordering, pagination behavior beyond max_results, or whether personal contacts and other contact groups are included.

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 short sentences, front-loaded with the action and scope, followed by the payload. No redundant or filler wording; every sentence carries information.

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, describing the returned fields is a needed addition and it is present. However, the listing behavior itself (result ordering, whether more contacts exist beyond max_results, account scoping) is left unstated, so the definition is adequate rather than complete.

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 both the account and max_results parameters are already documented in the schema, including the default of 20. The description adds no meaning beyond that, so the baseline of 3 applies.

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 gives a specific verb (list) and resource (contacts from the user's Google Contacts) plus the fields returned. It implicitly separates itself from contacts_get and contacts_search by being a bulk listing, but it never names those siblings, so an agent must infer the boundary.

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?

Usage is only implied: 'List contacts' suggests browsing the full contact set rather than a targeted lookup. The description never says when to prefer contacts_search or contacts_directory_search instead, which are the closest siblings and a real source of mis-selection.

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