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

With no annotations, the description carries the full burden and does substantial work: it discloses the price floor ($0.18/call), the settlement rail (USDC on Base via x402), and the exact failure mode for an unpaid call (structured payment requirements plus retry), which is the single most important behavior for an agent to anticipate. It stops short of latency, rate limits, or whether a retry without an idempotency key could double-charge.

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?

Four tight sentences with no filler, and the retry and sandbox guidance land early. The one structural weakness is that it opens on price and settlement rather than on what the tool does, pushing the actual capability explanation to the second sentence.

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 five-parameter tool with a nested context object, no annotations, and no output schema, the description supplies both the shape of a successful return and the shape of the unpaid error, which is the pair of outcomes an agent must handle. It leaves 'typed deliverable' undefined and says nothing about whether context values are echoed back or how long a synthesis takes.

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 mode enum, agent enum, context blob, messages array, and idempotency_key are all already documented in the schema, including the sharp warning that an unsupported mode is a 400 rather than a fallback. The prose adds nothing parameter-specific, so the baseline of 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?

The description states concretely what a call produces (growth diagnosis, the arithmetic behind it, concrete actions, a typed deliverable) and how it is billed, which is a specific verb-and-resource picture rather than a restatement of the name. It differentiates itself from one sibling by naming sandbox_call, but never positions itself against call_tool or call_action, so an agent must infer that this is the coach-specific variant.

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 explicit routing advice: use sandbox_call if you only need to see the shape, and expect a structured payment-requirements error that you can settle and retry without payment. What's missing is any guidance on choosing among the coach/payment siblings (call_tool, call_action, list_coaches) or when a paid call is warranted over a free one.

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