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

Annotations already declare readOnly, idempotent, non-destructive, openWorld, so the safety profile is covered. The description adds value beyond them by disclosing the response payload keys and the prerequisite sequencing relative to connect_audience_destination. It stops short of describing size/pagination of the audiences list or what happens for a non-activation destination.

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, front-loaded with purpose, then return shape, then the routing instruction. No filler, no restatement of the title, and the most decision-relevant clause (use before connect_audience_destination) closes the description.

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 helpfully enumerates the returned keys (fields, audiences, mappingGuidance) and the prerequisite workflow, which is enough for an agent to call it correctly. Minor gap: the shape of each returned item and the fact that workspace_id is required-but-unexplained are left unaddressed.

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 50%: destination_id is well documented in the schema (ID from list_destinations, must be activation_capable), but the description adds no meaning to it. workspace_id is undocumented in both places and the description does not compensate, so this sits at the baseline rather than above it.

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 ('Discover') and precise resource pair ('destination-side identifier fields and existing audiences') constrained to activation-capable destinations. It is clearly distinguishable from get_destination and get_destination_definitions, and the return shape is named up front.

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 prescribes ordering: 'Use this before connect_audience_destination', and tells the agent why (to pick the destination-side audience and valid mapping targets). It does not name a when-not case or an alternative discovery tool, but the activation-capable qualifier implicitly bounds usage.

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