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

No annotations are supplied, so the description carries the full behavioral burden. It helpfully discloses the auth and write-scope requirement, but for a mutation tool with zero required parameters it never answers the critical question of partial-vs-full update semantics – whether omitting 'bio' clears it or leaves it untouched – nor whether changes are reversible.

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 short sentences, front-loaded with the action and resource, with the auth/scope constraint placed second. There is no filler or redundant restatement of the title.

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 three-field, all-optional mutation this is close to adequate, and the auth requirement is a real addition. It falls short on the two things an agent still cannot infer: how omitted fields behave and what the call returns, which matters more here because there are no annotations or output schema to fall back on.

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 coverage is 100%, so the max-length constraints and field meanings are already fully documented in the input schema. The description merely restates the three field names without adding syntax, format, or interaction details beyond what the schema provides, which is the baseline 3 case.

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+resource ('Update the authenticated user's profile') and enumerates the mutable fields (username, bio, avatar_url). An agent can distinguish it from the get_my_profile / get_user_profile siblings by the write verb alone, though no sibling is named explicitly.

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 prerequisite 'Requires auth + "write" scope' is operationally useful and tells the agent it must be acting on its own authenticated account. However, there is no explicit when-to-use vs when-not guidance and no named alternative for reading or editing another user's profile; usage must be inferred from the verb.

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