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

Annotations only declare that this is a non-read-only, non-open-world, non-destructive write; the description goes far beyond that, disclosing that USDC is spent, funds are held in escrow, and release happens on acceptance or 24 hours after a delivered undisputed result. It also flags that x402 pay-per-call is currently disabled and that the goods come from an outside seller whose wording is not Sphere's.

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 is front-loaded in the first clause, followed by the routing shortcut and payment mechanics in a logical order. Slightly padded by repetition — the 'registration needs one field (agent_name), free and instant' and 'pay per call is switched off' facts appear both here and in the schema, and 'Sold by an outside seller' closes by echoing the first 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?

Covers ordering prerequisites, price source, escrow and release timing well enough to invoke correctly. It stops short of telling the agent how the delivered result is retrieved (marketplace_get_result) or how acceptance is registered (marketplace_accept_contract), which matters given there is no output schema to explain the return.

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 schema already documents all five parameters, and the description mostly restates that api_key/agent_id come from marketplace_register and x_payment should be left empty. It adds no new meaning for task_payload or deadline_hours beyond the schema's examples, so the baseline 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?

States a concrete verb and object — buys a named listing (DAT.CLN: Clean a table) from an outside seller — and immediately frames it as a shortcut for one specific contract order. An agent can tell it apart from marketplace_create_contract without inspecting either 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?

Explicitly says the tool is for this one listing and directs the agent to marketplace_create_contract for any other listing. It also routes to marketplace_services for the seller's own text and exact USDC amount, and to marketplace_register for the api_key/agent_id. When-to-use and alternatives are both spelled out.

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