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

Annotations already declare readOnlyHint=true and openWorldHint=false, so safety is covered. The description adds real value beyond that by disclosing what each catalog entry contains (inputs and example values), which tells the agent what a call returns even without an output schema.

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, zero filler: the catalog contents come first, the routing hint second. Every clause earns its place.

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 one-optional-param, read-only list tool with no output schema, the description covers scope, contents, and the follow-up action. Only the filtering behavior (what 'q' matches) is left implicit, a minor gap.

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 'q' parameter is documented in the schema with an example ('holdout', 'fees'). The description adds no filtering guidance of its own, 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 and resource ('List ... free Amazon and Meta ads calculators') and enumerates the items returned (holdout test size, incremental ROAS, break-even ROAS, ACoS, TACoS, fees, LTV/CAC). This makes it unmistakable from siblings how_lift_is_calculated and run_calculator.

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 routes the agent: 'Use run_calculator to run one,' making the list-vs-execute split clear. It doesn't address how_lift_is_calculated or when to prefer browsing over filtering, so not a full 5.

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