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

Annotations already declare this is a write operation (readOnlyHint=false, destructiveHint=false, openWorldHint=true). The description adds valuable context beyond annotations: supported formats, a 2 MB size cap, two input sources (dataBase64 or public HTTPS sourceUrl), authentication requirement, and that it returns the updated profile. It does not clarify whether an existing avatar is overwritten or describe failure modes, so it falls short of a perfect 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?

Two tightly written sentences with no wasted words, front-loading the core action and constraints before the authentication note. Every clause 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 3-parameter mutation tool with no output schema, the description covers input formats, size limit, source options, auth requirement, and return value at a high level. It could be more complete by clarifying overwrite behavior and failure handling, but it gives the agent enough to call the tool correctly.

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 67%, with contentType and sourceUrl documented in the schema and dataBase64 undocumented. The description adds meaning by listing accepted image types and the 2 MB limit, and clarifies that either dataBase64 or sourceUrl is used, but it does not explain the base64 encoding expectation or how sourceUrl/contentType interact.

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 (upload and set) and a specific resource (profile photo / your photo) in one step. It clearly differentiates the tool from general profile update siblings like me_update by focusing exclusively on the avatar.

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 usage (setting a profile photo) and gives a clear precondition: 'Signed-in (OAuth) connections only.' However, it does not explicitly say when to use this tool versus alternatives such as me_update, leaving usage guidance at an implied level.

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