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

Annotations already declare readOnlyHint=true, so the safety profile is covered. The description adds genuinely new behavioral context: max_members returns member resource names (not names/emails) that must be cross-referenced against list_contacts/search_contacts. It stops short of return format or error behavior, but the added output semantics are meaningful.

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 differentiation, then the account caveat. Three sentences with no filler, though the stacked parentheticals make it slightly dense.

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 extra burden but adequately explains the shape of the member results. A safe read tool needs little more; only pagination or error nuance is left unstated and is minor here.

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 goes beyond the schema by clarifying that member results are people resource names rather than display names/emails and telling the agent where to resolve them. It also contextualizes `account` in terms of connected Contacts accounts.

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 (Fetch), resource (Google Contacts groups/labels), and scope (by resource name). It explicitly distinguishes itself from the sibling list_contact_groups, so an agent can route correctly without opening either 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?

Explicitly names the alternative ('Unlike list_contact_groups') and the condition that selects the richer behavior (pass max_members > 0), plus the multi-account condition for `account`. When-to-use and when-not-to-use are both covered.

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