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

With annotations covering mutation and openness, the description adds substantial behavioral detail: USDC payment, escrow, release on acceptance or 24 hours after a delivered undisputed result, x402 being switched off, and registration requirements. It also warns that the service description in marketplace_services is seller-provided data, not Sphere's own description. These are meaningful operational traits beyond 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 front-loaded with the core purpose and then supplies payment, credential, and alternative-tool context. It is generally efficient, but some points such as x402 being switched off and the free/instant registration are repeated in the schema descriptions. The repeated 'Sold by an outside seller' at the end also adds little after the opening 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 complex paid contract tool, the description covers the purchase path, escrow behavior, credentials, payment unit, x402 status, and the alternative general tool. It does not describe what the call returns, and there is no output schema, so an agent still has to infer the immediate result of placing the order. Otherwise it is sufficiently complete 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 already 100%, so the parameter meanings are largely documented by the schema. The description reinforces that agent_id and api_key come from marketplace_register and that x_payment should be left empty, but it adds little syntax or format detail beyond what the schema already says. Baseline 3 is appropriate when the schema does the heavy lifting.

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: it buys the agent-exec code-sandbox service from an outside seller. It also distinguishes this shortcut from marketplace_create_contract, which is the general path for other listings. The scope is clear enough for an agent to select it over siblings.

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 explicitly says to use this as a shortcut for this one listing and to use marketplace_create_contract for any other listing. It also tells the agent to read marketplace_services for the seller's own description and the exact USDC amount. When-to-use and when-not-to-use guidance are both present.

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