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

Annotations already carry the safety profile (readOnlyHint=false, destructiveHint=false, openWorldHint=true, idempotentHint=false), so the bar is lower. The description still adds real value by describing the non-obvious output contract (watermarked preview, price, private link) and the image-size limit (~4 MB).

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 tight sentences: what it does and returns first, then how to supply the photo, then quality tips. Nothing is repeated and nothing is wasted.

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?

With no output schema, the description correctly takes on the job of explaining the return payload (preview image, size, price, private link), which is the most important gap it could have left. Minor omissions remain, such as whether the private link expires or how pricing is determined, but an agent has enough to call it correctly.

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 all five parameters, including the boards_tall/boards_wide grid constraints and size_id default, are already documented in the schema. The description's restatement of the image_url/image_base64 alternative adds little beyond it, so the baseline 3 applies.

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+resource (turn a photo into a brick mosaic) and enumerates exactly what comes back: a watermarked preview image, its size and price, and a private review/purchase link. The agent can tell this apart from get_brick_mosaic_options, which is referenced as the source of size ids.

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 concrete invocation guidance: supply the photo as image_url (a public https link) or image_base64, plus an explicit quality tip ("one person or pet, close-up, well lit"). It implies the size flow through get_brick_mosaic_options but never states explicitly when this tool should be preferred or when it should not be called.

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