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

Annotations already declare readOnlyHint=true and destructiveHint=false, so the read-only nature is covered. The description adds useful behavioral context beyond annotations: it shows the 'real' credit balance, presents output 'as a card', and clarifies that rendering/export limits are displayed alongside but are not credit-based. This goes beyond simple annotation restatement.

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 compact and front-loaded: the core purpose appears in the first sentence, followed by explicit usage triggers and a clarifying exclusion. Every sentence contributes useful information with no padding.

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 zero-parameter, read-only information tool with no output schema, the description fully covers what the tool does, when to use it, and what it does not cover. An agent has enough context to invoke it correctly and set appropriate user expectations.

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?

The tool has zero parameters and 100% schema coverage, so there is nothing about parameters for the description to explain. The baseline of 4 applies because no parameter-semantic burden exists.

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 uses a specific verb ('Show') and clearly identifies the resource: the user's real credit balance, plan, and usage limits, presented as a card. It also distinguishes the tool's scope from rendering/export limits, which are separate hour-based limits, making the purpose unmistakable even among many siblings.

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 explicitly states when to use the tool: when the user asks what they have left, or when a generation was refused due to insufficient credits. It also provides a when-not case by clarifying that rendering/export is a separate hour-based limit, not credits.

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