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

Annotations already declare readOnlyHint, idempotentHint, and destructiveHint=false, covering safety. The description adds valuable behavioral context: it's free and non-billable, and it recommends a specific ordering (before billable tools) to avoid unnecessary costs. This goes beyond the annotations by surfacing cost and workflow implications, while remaining consistent with them.

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 primary purpose is front-loaded in the first sentence, and the second sentence adds a clear directive for usage before billable tools. Every sentence earns its place, and the structure is immediately scannable.

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 tool with one parameter and no output schema, the description is quite complete: it covers what it checks (signals + freshness), cost implications, and recommended usage order. The only minor gap is that it doesn't enumerate which signals are returned, but that could vary per domain and is not essential for calling the tool correctly. Given the simplicity, the description provides sufficient context.

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?

Schema description coverage is 100%—the schema defines 'domain' as 'eCommerce domain, e.g. gymshark.com'. The description reinforces this by saying 'for an eCommerce domain' but adds no new parameter-level details. Since the schema fully documents the parameter, a baseline score of 3 is appropriate; the description doesn't need to compensate.

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 clearly states the tool checks which competitive signals RivalSweeper has for an eCommerce domain, including per-signal freshness. This distinguishes it from sibling tools that return actual signal data (e.g., get_competitor_price, get_promotions) by focusing on coverage rather than content. The verb 'check' and specific resource 'competitive signals...for an eCommerce domain' make the purpose unambiguous.

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 instructs to 'call this before any billable tool so you never pay for a domain we do not cover.' This gives clear when-to-use guidance and implies when not to use billable alternatives (when coverage is absent). It also contrasts with billable siblings, effectively routing the agent to this free preflight check.

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