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

Annotations already declare readOnlyHint=true and destructiveHint=false, so the safety profile is provided. The description adds context about what information is returned (plan, limits) but does not disclose additional behavioral traits such as authentication requirements or whether the info is cached. It is consistent with annotations, and the bar is lower given the existing hints.

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, tight sentence that immediately answers the core question (who is signed in) and then lists the key data points (plan, limits). Every phrase earns its place, with no filler or repetition.

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 the tool has no parameters, existing annotations for safety, and an output schema, the description fully covers the tool's purpose and scope. It clearly describes the type of information returned, and nothing important for correct selection appears missing.

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?

There are zero parameters and schema coverage is 100% (trivially). With no parameters to document, the description doesn't need to add parameter semantics. The baseline for zero-parameter tools is 4, and the description does nothing to reduce it.

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 clearly identifies what the tool does: reports the signed-in user, their plan, and applicable limits. It uses a specific, informative structure that distinguishes it from all sibling tools, which are all QR-code-centric and none of which relate to account or plan information.

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 when to use it: whenever account, plan, or rate-limit context is needed. It does not explicitly name alternatives or exclusions, but because no sibling tool covers this domain, the usage context is clear and unambiguous.

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