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

Annotations already establish the safe read-only, non-destructive, closed-world profile. The description adds meaningful context beyond that: the permission scope required (billing:read) and the account/key prerequisite. It still omits ordering guarantees, pagination, and whether the list is capped by 'Latest'.

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 compact fragments with zero filler. The core purpose is front-loaded, and the permission/account notes are clearly delimited in parentheses and brackets.

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, one-optional-parameter list tool with no output schema, the description adequately conveys what is returned (credit movements with payment references) and the auth context. It is slightly incomplete on limit behavior and result ordering, but nothing critical is missing for correct 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?

Schema description coverage is 0% for the single limit parameter, and the prose never mentions it. The schema supplies default 25 and max 100 but no meaning for the parameter, so the description fails to compensate for the coverage gap.

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 the resource clearly — credit movements — and enumerates the content types (top-ups, hourly usage, refunds) plus the included payment reference. It does not distinguish itself from adjacent siblings like list_invoices or get_balance, but an agent can identify the tool's function without opening the schema.

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 covers prerequisites (billing:read permission, free account + MCP key) but gives no guidance on when to choose this over get_balance, list_invoices, or other billing-related siblings. 'Latest' implies recent activity but is not framed as a selection rule.

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