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

Annotations already declare readOnlyHint, idempotentHint, and destructiveHint=false, so safety is covered. The description adds genuinely useful behavior context beyond that: it explains the `next_period_label` field semantics, the three possible scopes, and that it mirrors a specific REST endpoint — details an agent could not derive from the annotations.

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, front-loaded with the verb and resource, followed by the endpoint mapping. Dense but every clause carries information; the backtick-quoted field name is a minor readability cost but acceptable.

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?

With no output schema, the description carries the burden of describing returns and does so adequately by naming the fields each digest exposes. It omits pagination/ordering and exact response format, which are minor gaps for an account-scoped list.

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 takes zero parameters, so the schema baseline of 4 applies. The description adds no parameter meaning (there is none to add) but does describe the shape of the result records, which is the relevant substitute 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?

Specific verb+resource ('List this account's scheduled cost digests') with an explicit enumeration of what each entry contains (cadence, scope, destination, next due date). No sibling tool covers scheduled reports, so no collision risk, and the description preempts confusion by noting that create/edit are unavailable over MCP.

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 scope ('this account's') and the note that creating/editing scheduled reports is not available over MCP give clear boundaries for when this tool applies and when the agent must stop. There is no alternative sibling to route to, so no when-vs-alternative clause is needed.

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