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

Annotations already establish read-only, idempotent, non-destructive behavior; the description builds on this by warning that many costs may be zero, preventing incorrect assumptions about paid plans. It does not describe return structure, but that is acceptable given the simple retrieval nature and strong annotation coverage.

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 sentences with no wasted words. The first sentence lists exactly what the tool returns, and the second gives actionable usage guidance. Everything included earns its place.

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 one-parameter, read-only pricing lookup with rich annotations, the description fully enables an agent to decide when to call it and what it will contain. The lack of an output schema is not a gap since the returned pricing info is naturally described by the tool's purpose.

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 only parameter, include_backends, is already fully documented in the schema with a default and a clear explanation. The tool description mentions per-backend costs but adds no semantic detail beyond what the schema provides; the schema carries the load here.

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?

States the exact resource being retrieved: the Yappy app's free Mac app, per-backend language-model costs, and public API terms. This clearly distinguishes it from siblings like get_frequently_asked, list_product_features, and get_system_requirements, which address different information needs.

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?

Provides an explicit trigger: 'Call this before telling a user about price.' It also adds important context that most of the product is free and some backend options cost nothing, so the agent should not assume paid pricing. Though it doesn't name alternatives, the sibling set makes the pricing tool's unique role obvious.

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