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

Annotations already declare readOnlyHint=false and destructiveHint=false, so the write-nature is clear. The description adds the scoping detail 'authenticated user's', which is useful behavioral context not in the annotations. However, it does not disclose any side effects, validation rules, or effects on existing avatars, so it only moderately adds beyond 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?

A single sentence with zero waste. The verb 'Update' is front-loaded, the resource is specific, and the intended user scope is included without unnecessary detail.

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?

For a one-parameter tool with full schema coverage and an output schema present, the description is adequate. It states the action and the target user. The only minor omission would be explicit mention of accepted formats or side effects, but the schema's 'any image URL' and presence of an output schema reduce the need.

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% and the parameter description already explains that avatar_url is 'Profile picture URL or path — optionally a Media URL, or any image URL'. The tool description adds minimal extra meaning by clarifying it is the authenticated user's profile picture, but does not need to compensate for schema gaps. 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 states a specific verb and resource: 'Update the authenticated user's profile picture'. It clearly distinguishes this tool from siblings like update_my_profile (profile fields) and update_user (admin updates other users) by specifying it targets the avatar of the authenticated user.

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?

The description implies the tool is for the authenticated user's own avatar but does not explicitly state when to use it versus alternatives like update_my_profile or update_user. No exclusions or conditional guidance is provided, so the usage context is only implicit.

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