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

Annotations already declare readOnlyHint=true and openWorldHint=false, so the safe read-only nature is covered. The description adds the auth requirement ('Needs the organization key') and the exact data scope (monthly free checks, prepaid credits), which is useful context beyond the annotations.

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: the first states what is returned, the second states the prerequisite. It is front-loaded and every word carries information, with no filler.

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 no-parameter, read-only tool with no output schema, the description tells the agent what data is returned and what credential is needed. Annotations carry the safety profile, so nothing critical for correct invocation is 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?

With zero parameters, the schema is empty and the baseline is 4. The description adds meaningful invocation context by stating that an organization key is required, even though that key is not represented as a parameter 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 names the specific resource it returns ('free checks left this month and your prepaid credits') but omits an explicit verb like 'get' or 'return'. It still distinguishes the tool from siblings such as guard_check and guard_buy_credits by focusing on balance information rather than checks or purchases.

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?

There is no guidance on when to use this tool instead of guard_check, guard_buy_credits, or guard_pricing. The phrase 'Needs the organization key' is a prerequisite, not a routing condition or alternative comparison.

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