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

Annotations already declare readOnlyHint=true, so the safety behavior is covered. The description adds meaningful behavioral context beyond that: it works before any group exists, returns an empty list when no prospect belongs to a campaign, and only lists the current shared agent when operating one. This helps the agent anticipate actual results.

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?

The description is compact and front-loaded, stating the core purpose in the first sentence and adding only relevant usage context afterward. The returns section is a single focused sentence. No filler or redundant restatement of the title exists.

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?

For a zero-parameter, read-only tool with no output schema, the description is complete: it states what the tool returns, the exact data shape, the empty-case behavior, when to use it, and when to use the alternative. An agent can invoke it correctly without additional inference.

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?

The tool has zero parameters and schema description coverage is 100%, so there is no parameter ambiguity to resolve. The description still adds semantic value by explaining that the result feeds criteria.agent_ids, which helps the agent understand how to use the returned data.

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 clearly identifies the action ('List every campaign') and the exact resource scope ('the user's (team-wide) prospects belong to'), then explains why this output matters ('the options for a new message tag group's or segment group's criteria.agent_ids'). This distinguishes it from sibling list tools like list_agents or list_message_tag_groups by tying it to a specific downstream use.

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?

It gives explicit usage timing: 'read it when setting up the first group' and clearly states when to prefer an alternative ('once groups exist, each group's classifiable_campaigns carries the same list'). The shared-agent scoping note adds another practical decision rule.

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