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 genuine behavioral context beyond that: what the two discovery enums actually return (usage counts, already-seen event names) and the failure mode that filters naming non-existent fields 'silently match zero contacts forever.' It stops short of noting limits/pagination, but the added caveat is substantive.

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 sentences, purpose and rationale front-loaded before the enum specifics. Efficient, though the second sentence largely re-narrates what the schema's enum description already says, so a little redundancy is present.

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 readOnly annotations, a full enum schema, and an output schema, the description only needs to add routing and rationale, which it does. The main remaining gap is that return shape and any list limits are left entirely to the output schema, which is acceptable 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% and the enum's own description already documents every value, including the same contact_fields/event_names guidance and the zero-match warning. The description restates rather than extends that, so per the high-coverage baseline a 3 is appropriate.

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+resource ('List existing resources of one kind') and immediately gives the goal ('find ids and avoid duplicating work'). It also distinguishes the discovery pair (contact_fields, event_names) from the summary lists, and implicitly separates itself from the get_* siblings. An agent can tell what this does without opening the 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?

Gives clear context for when to call it: 'use to find ids and avoid duplicating work' and explicitly 'call those before writing segment conditions or workflow triggers.' This is real when-to-use guidance with a rationale, though it does not state when NOT to use the tool or name the alternative get_* tools inside the description proper.

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