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

Annotations already declare readOnlyHint=true, openWorldHint=true, idempotentHint=true, and destructiveHint=false, so the safety profile is fully covered. The description adds the 'free' cost context, which is a meaningful behavioral trait beyond the annotations, but it doesn't disclose other traits like rate limits or data freshness.

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 a single compact sentence that front-loads the core operation ('Read current rate card') and appends the cost qualifier. Every word earns its place, and there is no redundancy with the schema or annotations.

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 tool with rich annotations, the description is nearly complete. The only minor gap is that it doesn't describe the return format or whether the rate card is paginated, but the absence of an output schema and the simplicity of the operation make this a minor omission.

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 and 100% schema coverage, the schema is trivially complete. The description adds the 'current' qualifier, implying the rate card is the latest version, which is a small but useful semantic addition beyond the empty 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 'Read current rate card; free' clearly identifies the operation (read) and the resource (current rate card), and the 'free' qualifier adds a useful distinction. It doesn't explicitly name sibling tools, but the verb+resource combination is specific enough to distinguish it from most siblings like get_balance or get_usage.

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 this is a read-only, no-cost operation, which gives some context for when to use it. However, it doesn't explicitly state when to prefer this over alternatives or mention any exclusions, leaving the agent to infer usage from the 'read' and 'free' cues.

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