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

Annotations already mark the tool as read-only and non-destructive; the description adds valuable context by stating the ledger is 'append-only' and enumerating event types like credit.grant, credit.purchase, credit.debit, and credit.balance_snapshot. This gives the agent a clearer picture of the data without contradicting 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?

The description is a single dense sentence with no filler. It front-loads the resource and endpoint, then packs the relevant event types into a compact, scannable list. Every part contributes to understanding the tool.

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 tool with annotations covering safety, the description is mostly complete: it names the endpoint, scoping, and event categories. It omits details like pagination, ordering, or response shape, but since no output schema exists and the tool is simple, the description provides sufficient context for selection and invocation.

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 input schema is empty with 100% coverage, so the baseline is 4. The description goes beyond by clarifying that events are implicitly scoped to 'this caller_id' and by describing what kinds of events appear in the ledger, which helps the agent understand how the tool is parameterized without explicit parameters.

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 identifies a specific resource (credit ledger events), the relevant endpoint (GET /credits/events), and the event types returned. It does not use an explicit verb like 'list' or 'get,' but the GET path plus event-type enumeration makes the purpose clear. It is distinguishable from siblings like credit_balance and list_credit_packs, though it doesn't explicitly contrast with them.

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 phrase 'for this caller_id' implies this tool is for viewing the calling account's own credit ledger history. However, there is no explicit guidance about when to prefer this tool over related siblings such as credit_balance or list_credit_packs, and no when-not-to-use conditions.

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