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

With no annotations, the description carries the full burden. It only states billing cost and group ('other'), but fails to disclose whether the operation is read-only, what happens on invalid tokens, or any side effects. The name implies a read operation but it is not explicitly stated, and no other behavior is disclosed.

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?

The description is extremely short, but this is under-specification rather than concise efficiency. It contains only a title-like phrase and billing info, lacking any substantive structure or details. It does not earn its brevity.

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?

Given 4 parameters, no annotations, and no output schema, the description is severely incomplete. It does not mention the return format, error behavior, authentication requirements, or any prerequisites. This is inadequate for an agent to use 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 0%, so the description must explain the parameters. It only implies auth_token's role via the tool name, but does not clarify apiKey, proxyUrl, or resFormat. The description adds almost no value beyond the parameter names in the schema.

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 the tool gets the username (with example @elonmusk) based on an auth token, which is a specific verb+resource. It distinguishes from the sibling getUserIdByToken by explicitly naming 'UserName', and the GET/POST variants are clear from the tool name. However, it somewhat restates the title without adding much nuance beyond the example.

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?

No guidance is given on when to use this tool versus alternatives. It does not mention conditions like 'use this when you need the username instead of user ID' or when to prefer the GET over POST variant. The description provides no usage context or exclusions.

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