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

No annotations, so the description carries the full burden and does well: it discloses pricing, the x402 payment flow, that anyone may pay, settlement behavior ('Nothing settles' on 400), and precise error codes 400/409. However, the score is capped because several disclosures live in schema descriptions and it never states permission/signing requirements beyond a passing mention of the payer — solid but not exhaustive for a paid mutation.

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?

Front-loaded with the core behavior and organized into labeled sections (Cost, Inputs, Returns, Errors, Next) that are easy to scan. Slightly penalized for redundancy — the 0.005 USDC/20-unit pricing is repeated three times across the first line, the Cost bullet, and the closing paragraph.

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?

Despite no output schema, the description documents the return shape (units.bought, units.balance) and enumerates both failure modes with their codes. For a 2-param paid mutation, an agent has everything needed to call it, interpret the result, and recover from errors.

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 coverage is 100%, so the baseline is 3, but the description adds real meaning beyond the schema: it explains that `units` drives the 402 price, that a missing/under-minimum value is priced then refused with 400, and that `address` is case-insensitive and keyed. This enriches how the agent should set the params.

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 a specific verb+resource ('Adds units to an existing box's balance') with pricing inline, and immediately distinguishes itself from siblings by naming boxCreate, boxStatus, and watchList as the create/read/follow-up tools. An agent can tell this apart from boxTopUp and boxCreate without opening any 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?

Explains exactly when it's needed ('a box with none has its watches paused until this is called') and routes to alternatives: use boxCreate if 409 box_required, then boxStatus to read balance, watchList to confirm watches resumed. Exclusions (anyone may pay, not only the owner) are explicit.

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