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

readOnlyHint=true already signals a safe read, so the bar is lower, but the description still adds real context: shared-agent scope behavior ('lists only the current shared agent') and the empty-state semantics. It does not, however, mention pagination or ordering, which is a minor gap.

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, then gives the when-to-use routing and a separate returns block. Every sentence earns its place with no repetition, and structured tags aid scanning.

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?

A read-only list tool with no output schema, yet the description supplies the return shape (campaigns list of {agent_id, name}) and the empty condition. Combined with the annotation, an agent has everything needed to call and interpret it correctly.

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% and the single on_behalf_of parameter is fully documented in the schema, including its agency-client semantics and the omit-to-act-on-own-account default. The description adds no parameter detail beyond that, so baseline 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?

States a specific verb (list) and resource (campaigns) with the exact scope: campaigns the user's/team's prospects belong to, framed as the valid options for criteria.agent_ids. This clearly distinguishes it from siblings like list_message_tag_groups and list_segment_groups.

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 says when to use it ('read it when setting up the first group') and when it becomes redundant ('once groups exist, each group's classifiable_campaigns carries the same list'), effectively naming an alternative source. Routing is unambiguous.

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