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

Annotations already declare non-readonly, non-destructive, non-idempotent and closed-world, so the safety bar is partly covered; the description adds meaningful behavior on top: 'No AI is used', how each layout positions text, and what is returned (media_uid and url). It does not mention cost, quotas, or image dimensions/aspect ratio, which keeps it from a 5.

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 core action, then layouts, then the parameter and return notes; every clause carries information. The layout list and parentheticals make it dense and slightly hard to scan, but there is no filler.

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 states the return values (media_uid, url) and covers layouts, variants, photo sourcing, and the photo_url requirement for non-text_only layouts. Gaps remain around image dimensions, failure modes, and whether generation costs credits, but nothing needed to invoke it correctly is missing.

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 only 50%, so the description must compensate, and it does: it explains what each cryptic enum value means visually (photo_and_text = text band under the photo, photo_card = text above the photo), clarifies the photo_url source, and gives variant real meaning ('picks other brand colour combinations'). The headline and small_text parameters get no elaboration here, but small_text is already documented in 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?

States a concrete verb and output ('Put a headline ... on a photo, or on its own, in the workspace's brand colours and logo'), names the brand source (Feedlio), and enumerates all four layouts. No sibling tool produces images, and the description makes that distinction obvious.

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 practical when-to-use context by routing the agent upstream ('photo_url is the url of a Media Library image (from list_media or add_stock_photo)') and downstream ('Returns media_uid (for create_post)'). It lacks explicit exclusions — e.g. when to use this instead of text-only editing or when not to use it alongside add_stock_photo — so it stops short of a full 5.

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