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

With no annotations, the description carries the burden well: it discloses billing behavior (1 CRD per call, charged even on rejection, 429 costs nothing) and error semantics (request_id to quote to support). It does not mention auth requirements or whether the call is read-only, though the metric list implies a read.

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?

Three short, front-loaded sentences: what it returns, over what window, then cost and error policy. Every clause carries operational information an agent needs before spending credits; nothing is redundant.

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 no-output-schema analytics read, the description tells the agent what dimensions and measures come back, the default window, the cost and the error contract. Only auth expectations (api_key header alternative) and rate-limit limits themselves are left implicit, which the schema partially covers.

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 coverage is 100%, so all four parameters are documented in the schema itself, and the description only restates the `days` semantics (default 30, 0 = all time) that the schema already contains. Nothing extra is added for api_key, project_id or x402_payment beyond what the schema says, so baseline 3 applies.

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+resource (signup attribution breakdown) plus the grouping dimension (per signup_host), the exact metrics returned (users, purchases, revenue) and the time window. No sibling tool in the list does analytics, so this is unambiguous and instantly distinguishable from the transaction/user CRUD siblings.

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 clear operating context: default window of 30 days, that 0 means all time, and the credit cost per call. It does not state when NOT to call it or any alternative tool, but no sibling offers comparable reporting, so there is little ambiguity left. The exclusion is minor rather than harmful.

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