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

Annotations only declare non-read-only, non-destructive, closed-world; the description adds genuinely new behavior: accepted formats, a 512 KB cap, base64 encoding, server-side re-encoding, and moderator approval before display. That approval pipeline is the key non-obvious trait. It stops short of saying whether the call returns immediately with a pending status or blocks until approval.

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?

Two dense sentences, front-loaded with the action and followed by the constraints that matter; nothing is padded or redundant. The format/size details are packed parenthetically, which keeps it tight.

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?

An output schema exists, so return values need no explanation, and the description covers the constraints an agent needs to build a valid call. The remaining gap is the moderation lifecycle and the undocumented auth parameter, both minor for a two-parameter upload tool.

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 0%, so the description has to carry parameter meaning; it partially does by constraining image_base64 (PNG/JPEG/WebP/GIF, max 512 KB, base64). The api_key parameter is never mentioned, and the description doesn't say whether the base64 string may include a data-URI prefix.

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 ("Upload your own profile image") with scope ("your own"), so an agent knows it operates on the caller's avatar. It does not, however, distinguish itself from the sibling tool `set_avatar`, which an agent could easily confuse with this one.

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?

There is no explicit when-to-use or when-not-to-use guidance, and the nearby `set_avatar` sibling is never mentioned as an alternative or contrast. The agent must infer from context alone that this is the upload path rather than the set path.

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