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

Annotations already declare idempotentHint=true and destructiveHint=false, so the description's idempotency statement aligns but adds value by explaining already_saved behavior and billing details. It also discloses that saving incurs costs for ads and creatives but is free for others, which is crucial for agent decisions. However, it does not detail output schema, but since idempotency and cost are covered, a 4 is appropriate.

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 dense and well-structured, with key information front-loaded (what it saves and what entity types are supported), followed by specific requirements and billing. Every sentence serves a purpose, and the use of bold for critical notes (MUST, OPTIONAL, BILLING) enhances scannability without waste.

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?

Despite having an output schema, the description still explains return behavior (already_saved) and billing, which are not fully captured in the schema. It covers all necessary details for correct invocation: entity type mapping, source of IDs, special hub requirement, folder naming guidance, and cost implications. This is complete for an agent to use safely.

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 description largely repeats parameter info. It adds minimal extra meaning, like clarifying that 'ids' must come from search results and that 'hub' is only required for hub entity type, but this is already in the schema descriptions. The billing details per entity_type add some value but not beyond what the schema implies.

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 states the tool saves a selection of entities to favorites folders, naming the valid entity types and how IDs are sourced. It distinguishes itself from sibling search and get tools by focusing on the save action, and the detailed breakdown of entity types and required parameters makes the purpose unambiguous.

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?

The description explicitly explains when to use this tool (to save entities for later review) and provides guidance on prerequisite sources (search_* tools), the required hub parameter for hub entities, and folder naming preferences. It also indicates when it is not applicable (e.g., no duplication) and implies alternatives like list_favorites for reviewing saved items.

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