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

Annotations already declare the write/network profile (readOnlyHint=false, openWorldHint=true, idempotentHint=false), so the bar is lower. The description still adds real context beyond the schema: server-side fetch semantics, the public-address/no-redirect constraint, and size ceilings, and it names the return value (assetId).

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?

A single dense paragraph that front-loads the core action, then constraints, then return value. Every clause carries information (formats, limits, video exclusion, downstream use) with 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?

There is no output schema, and the description supplies the missing return contract (assetId and where to pass it), the input-mode constraints, and the failure-relevant limits (size, video unsupported). Nothing an agent needs to invoke this correctly is absent.

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 schema already documents all four parameters, including the base64 prefix requirement and URL size caps. The description largely restates those same format details rather than adding new semantics (e.g., tag usage or interaction between parameters), 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?

The description opens with a specific verb+resource ("Saves an image into the brand's image library") and immediately scopes what it accepts. It is clearly distinguishable from siblings like set_brand_logo or attach_post_media without opening either schema.

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 states the two accepted input modes, rules out video, and routes oversized/video uploads to the Rebbel dashboard, plus names the downstream consumers (attach_post_media, create_adhoc_post). It stops short of an explicit contrast with set_brand_logo, which is the nearest ambiguous sibling.

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