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

Annotations cover the safety profile (readOnlyHint=false, idempotentHint=false, destructiveHint=false), but the description adds genuinely useful context beyond them: applying costs no Ad Run credit and consumes no AI turn. It does not say whether an existing hero image is replaced, which is the main remaining behavioral unknown.

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?

Front-loaded with the action in the first sentence, followed by tight argument definitions and a one-line return shape. No filler; the Args list is warranted given the empty schema descriptions.

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 mutation tool with no output schema, the description supplies the return shape ({ ideaId, imageUrl, applied }) and cost behavior, which is what an agent needs to call it confidently. It omits the response_format parameter and overwrite semantics, minor but real gaps.

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?

With schema description coverage at 0%, the description carries the burden and does so well, documenting all three required params and cross-referencing selectedResultId's origin in idealaunch_get_image_job. The fourth parameter, response_format, is left undocumented in both schema and description.

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?

A specific verb ('Set ... as the idea's hero image') plus the exact resource being mutated. It is clearly distinguishable from the sibling idealaunch_generate_hero_image, which creates the image rather than applying one.

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 establishes a prerequisite chain: jobId must be 'a succeeded image job' and selectedResultId is 'the variant id from idealaunch_get_image_job', routing the agent to the correct upstream tool. It does not state what happens if no image job exists yet or how this interacts with the generate sibling, so it falls short of full when/when-not guidance.

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