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

Annotations already declare readOnlyHint=true, destructiveHint=false, and openWorldHint=false, so the safety profile is covered. The description adds real behavioral context beyond that: the price is read live rather than fixed, and a check runs a waterfall of up to two providers with one billable credit per verdict returned, so cost is 1 credit on first-provider rejection and 2 when both answer. It omits latency or error behavior, but adds meaningful operational detail.

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 purpose is front-loaded in the first sentence, which is good. However, the second sentence ('The price is read live, never a fixed figure') largely restates the first, and the waterfall sentence is dense — the description is informative but has some redundancy and could be tighter.

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 pricing query with no output schema, the description must carry the return-value burden, and it does name the specific price fields and explain the credit-cost model (1 or 2 credits). It does not enumerate the full response shape or structure, which is a minor gap given the simplicity of the tool.

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 tool has zero parameters, so the baseline is 4. The description still introduces the pricing fields (perAddressCeilingUsd, perAddressFloorUsd) that frame the caller's budgeting logic, though this is contextual rather than parameter semantics. Nothing in the schema is left unexplained.

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 a specific verb and resource — returns the current per-address email verification cost from the live billing plan. It defines the billing unit (verification credit) precisely and is distinguishable from siblings like get_credit_balance, which reports balances rather than per-check price.

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?

Gives concrete guidance on how to use the returned figure: budget against perAddressCeilingUsd, the common case, not perAddressFloorUsd. It does not explicitly route the agent away from billing siblings or state prerequisites, but the framing ('what one email verification costs right now') makes the intended use clear.

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