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

Annotations only tell the agent this is a non-read-only, non-destructive operation; the description goes further by disclosing that it consumes credits per variant and that omitting `variants` triggers a default render of all four. That cost/default behavior is exactly the kind of context annotations cannot carry. It stops short of explaining what happens to existing images or how results are retrieved.

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 short sentences, front-loaded with the action and cost warning. The closing line ('The images are what makes a board usable as a visual reference') is mild editorializing, but it is the only sentence that does not carry operational 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 credit-consuming generation tool with no output schema, the description covers the essentials: what it produces, what it costs, and the default expansion behavior. It leaves minor gaps around where generated images land and whether re-runs overwrite, but nothing that would cause a bad call.

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%, so the allowed variant values and the omit-for-all behavior are already documented in the schema itself. The description largely restates that ('Without `variants` the backend renders all four') rather than adding syntax or format detail beyond the schema. Baseline 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 verb and resource: 'Generate time-of-day reference images for a location board.' An agent knows what is produced and against which artifact. It does not, however, distinguish itself from near neighbors like lab_restyle_location or lab_location_panorama, so the sibling differentiation is only implied by 'time-of-day variants.'

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 prescribes a workflow step in 'check the price with get_cost first,' which is genuine usage guidance for the cost-check parameter. But it never states when to prefer this tool over alternatives such as lab_restyle_location or lab_create_location, nor does it note prerequisites like an existing board. Usage is implied rather than argued.

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