Choose which thumbnails are live

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

With no annotations provided, the description carries the full burden. It comprehensively discloses: the change is immediate, affects what Roblox serves to players, nothing is deleted, and inactive variants can be brought back. This covers destruction (none), side effects (immediate applicability), and reversibility, which is excellent given the absence of annotations.

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?

The description is a single compact paragraph that is front-loaded with the core purpose, then logically moves to input formats, modes, and consequences. Every sentence adds meaningful information, with zero filler. It is appropriately sized for the tool's complexity.

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?

Given the moderate complexity of three parameters and no output schema, the description is complete. It covers all essential aspects: behavior, modes, id handling, and side effects. No important information is missing, and the integration with get_thumbnails is mentioned.

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 baseline is 3, but the description adds significant semantic value: it explains that ids accept two types (asset ids from get_thumbnails or internal thumbnail ids) and gives precise meaning to each mode. It goes beyond the schema's enum descriptions by advising on typical usage ('which is what you usually want'). This is clear added value beyond the schema.

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?

The description clearly states that the tool changes which thumbnails are live on the homepage, with a specific verb ('change') and resource ('game's thumbnails'). It distinguishes itself from siblings like get_thumbnails (which retrieves) and upload_thumbnail (which creates) by focusing on setting the live set.

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?

It explicitly explains when to use each mode ('replace' vs 'add'/'remove'), and tells the agent that 'add' or 'remove' is 'what you usually want when acting on one thumbnail.' It does not explicitly mention alternative tools, but the clear mode guidance serves the purpose of guiding usage. The description also specifies that ids can come from get_thumbnails, linking to the workflow.

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