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

Adds substantial context beyond the annotations (which only say non-readonly, non-destructive, closed-world): free/no payment, per-agent 24h rate limit, auto-registration returning agent_id and key, and the signed contract record verifiable via marketplace_verify_signature. That is rich disclosure an agent cannot get from the structured fields.

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-loads the free offer and the core action, and every clause carries information (limits, key behavior, payload shape). Dense with parentheticals that hurt skimmability slightly, but no filler sentences.

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 no output schema and a nested task_payload, the description supplies what an agent needs: the expected return (receipt with per-claim verdict, plus agent_id/key on first call), the payload format, and post-call verification. Nothing essential is missing for a 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 coverage is 100% (baseline 3), but the description adds real value by giving the concrete task_payload shape ({result, claims, source_text}), which the schema's generic {question}/{image_path} example does not convey. Minor gap: deadline_hours and x_payment intent only lightly touched.

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 action and output: 'Send a result and claims about it: Sphere checks them at once and returns a receipt with a verdict per claim.' An agent can tell it verifies claims and returns a signed receipt, distinct from generic buy_* siblings and from the paid buy_sphere_receipt by the explicit 'free first order / trial' framing.

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?

Explicit when-to-use and conditions: free, no balance/402, one per agent per 24 hours, no key needed on first trial, and names alternatives (marketplace_register for key, marketplace_services for other purchases). Routing is unambiguous.

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