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

Annotations already cover safety (readOnlyHint, idempotentHint, openWorldHint), so the description's added value is the reliability filter threshold, the ordering rule, and the full return field list. It doesn't mention pagination limits beyond the schema or freshness windows for the reliability window itself, but the substance is well above the annotation bar.

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?

Two well-organized sentences, leading with the trigger condition and following with the return payload. The return-field enumeration is long but earns its place by telling the agent what it can filter or report on; a minor trim would still convey it.

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 an output schema present the description needn't document returns formally, yet it still summarizes each field including the statistical measure (95% upper bound on failure rate) that an agent needs to interpret reliability. Read-only, idempotent, open-world behavior is fully accounted for.

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% and both parameters are documented with defaults (50 when omitted) and enum semantics (omit to list every kind). The description adds no parameter detail beyond the schema, 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 specific verb and resource (list reliable sellers) with the exact reliability criterion: zero failures across at least 30 paid calls, sorted most-called first. Easily distinguished from siblings check_x402_seller (single-seller lookup) and recent_changes (change feed).

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 names the triggering situation: 'Call this when choosing among sellers for a task, or when the user asks for a safe or reliable API.' The sibling check_x402_seller is implicitly the per-seller counterpart, and no exclusions are needed given the criteria are self-selecting.

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