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

Beyond the annotations it discloses substantial behavior: bearer-token auth via header with credentials forbidden in arguments, one purchase per MCP request, receipt retention, same-identifier retry on lost replies, and the explicit statement that configuration does not guarantee live readiness and the route response is authoritative. This is exactly the mutation/auth/idempotency context an agent needs.

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?

Purpose and credentials lead the description, and the seven sentences are dense with operational constraints rather than filler. It is on the long side, but each sentence carries a distinct rule (retry, budget, limits) that would otherwise be lost.

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 an output schema present, the description need not describe return values, and it still covers authentication, idempotent retry semantics, enforcement conditions, and explicit non-capabilities. An agent has everything required to invoke this purchase safely.

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 100%, so the four parameters are already fully documented, and the description largely repeats them ('Supply an explicit operationId, grantId, domain and maxSpendUsd'). Its only added nuance is the reminder that retries reuse the same identifier and that the spend ceiling will not be inferred or auto-raised, which the schema already conveys.

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 states a specific verb and resource: buying the current_appraisal service against a prepaid account and a funded grant, with the required identifiers named. However, it never distinguishes itself from the near-identical sibling buy_appraisal, so an agent cannot tell from the text alone which of the two to select.

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?

It gives a clear context of use (prepaid account plus an existing operator grant) and explicit exclusions ('cannot fund the account, create grants or raise a limit'). It does not, however, name sibling alternatives such as buy_appraisal or inspect_agent_grants, so the routing decision remains partly inferential.

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