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

Annotations already declare readOnlyHint, openWorldHint, idempotentHint, and non-destructive behavior. The description adds valuable context beyond those annotations by specifying that this call is free and does not spend credits, which is important operational information for an agent deciding whether to use it.

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 compact and front-loaded with the essential purpose, followed by the usage context and a concrete example. Every sentence earns its place with no redundant 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 simple two-parameter count tool with complete schema coverage and safety annotations, the description is sufficiently complete. It covers what the tool returns, the key usage distinction, authentication format, and a runnable example.

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% and both domain and _apiKey are fully documented in the input schema. The description's inline example matches the schema and demonstrates the call shape but does not add meaning beyond what the schema already provides, so the baseline of 3 is appropriate.

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's purpose as counting Snov.io email addresses for a domain, using a specific verb and resource. It also explicitly distinguishes itself from the sibling snov_domain_search by calling it a 'free pre-check' for the full search, making the distinction clear.

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 states when to use this tool: as a free pre-check before spending credits on snov_domain_search. It names the alternative tool directly and gives a clear decision condition, so an agent knows not to use the heavier search until this count is reviewed.

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