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

Annotations already declare readOnlyHint=true, and the description is consistent with a read-only call. Beyond that it discloses real behavioral facts: credits are earn-only, nothing consumes them, they have no monetary value, cannot be transferred or cashed out, and an API key is required – useful context that prevents an agent from attempting spend or transfer operations.

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?

Front-loaded with what is returned, followed by the credit semantics and the auth note. The three sentences ruling out buying, selling, transferring and cashing out are slightly repetitive but each heads off a plausible agent misconception.

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 no-required-param read tool with no output schema, the description says enough: what comes back (balance plus 50 changes), what credits mean, and the auth requirement. Little an agent needs 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?

There is a single optional api_key parameter with 100% schema description coverage, so the schema already explains the only input. 'Needs your key' adds the auth hint but no format or header-vs-parameter detail beyond the schema; baseline 3 applies.

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 a specific resource and return content: the credit balance plus the last 50 credit changes. No sibling tool deals with credits, so confusion risk is low, though it never explicitly contrasts with any sibling.

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?

Usage is only implied – the agent can infer this is the read call for credit status, and 'Needs your key' signals an auth prerequisite. There are no explicit when-to-use or when-not-to-use conditions, but no sibling overlaps this resource either.

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