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

The description only restates the mutating intent already implied by the annotations (readOnlyHint=false). It adds no details about validation, image requirements, side effects, or what happens to the previous avatar beyond the parameter description.

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, front-loaded sentence that conveys the essential purpose with no wasted words. Every word earns its place.

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 simple self-service avatar update with one fully documented parameter and an output schema, the definition is largely complete. The only notable gap is the lack of explicit distinction from update_my_profile and update_user.

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 avatar_url parameter is already described as a profile picture URL or path. The description adds little beyond the schema, so the baseline score of 3 is appropriate.

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 ('Update') and resource ('authenticated user's profile picture'), making the tool's function clear. It does not explicitly contrast with siblings like update_my_profile or update_user, but the focus on the current user's avatar is sufficiently distinct.

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 guidance on when to use this tool rather than update_my_profile or update_user. The phrase 'authenticated user's' implies self-service scope, but no exclusions or alternative tools are mentioned, leaving the agent to infer usage.

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