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

Annotations already declare the safety profile (readOnlyHint false, destructiveHint false), so the description's main contribution is the auth requirement 'Needs listings:write', which is real operational context an agent needs before calling. It doesn't mention what happens to the previously set cover, which is the one behavioral gap.

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 short sentences: the action and scope first, then the permission requirement. No filler, no restated title, nothing that could be cut without losing information.

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 two-parameter mutation with an output schema present, the definition covers what the tool does, the data source for the id, and the required scope. The only shortfall is not saying what happens to the prior cover or whether the listing must be in a certain state.

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 both parameter descriptions already explain productId and photoId and their provenance. The description repeats the get_my_listing sourcing hint without adding format or validation detail beyond the schema, making the baseline 3 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 verb and resource — making a listing photo the cover its page leads with — and implicitly contrasts with add_listing_image and remove_listing_photo by scoping the action to 'cover' selection. An agent can tell exactly which sibling this is versus the other photo tools.

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?

Gives clear context for invocation by naming the prerequisite data source (photo id from get_my_listing) and the required permission (listings:write). It doesn't state explicit exclusions or when-not-to-use, but the sibling set has little overlap with this narrow action.

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