What changed for an advertiser

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

Annotations declare readOnlyHint=true and idempotentHint=true, but the description says the first call records a baseline and later calls report movement. This is a persistent server-side side effect and repeated identical calls intentionally return different results, directly contradicting the idempotent and read-only hints. Flagged as Annotation Contradiction.

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?

Three sentences, front-loaded with the core purpose, then the key stateful caveat, then the sibling distinction. Every sentence earns its place and there is no filler.

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 low-complexity tool with a full schema and an output schema, the description provides the needed operational details: baseline behavior, expected first-use outcome, and when to call again. It is nearly complete, but the contradiction between the stateful behavior and the idempotent/read-only annotations leaves some context unresolved.

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%, with all three parameters documented including the limit consistency note and country default. The description itself adds no extra parameter semantics, so the baseline of 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 action (compare/report changes) on a specific resource (advertiser's ads), and immediately distinguishes itself from siblings: 'the only tool here that answers what changed rather than what is running.' An agent can tell what it 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?

Explicitly handles the first-call case (records a baseline, reports nothing changed) and tells the agent to call again later to see movement. It also names the conceptual alternative category, tools describing what is running, so an agent knows when not to use it.

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