eBay fees for one order

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

Annotations already cover safety (readOnly, idempotent, non-destructive, closed-world), so the bar is lower. The description still adds real behavior: strict validation that names the offending field rather than silently adjusting input, the no-Store-subscription rate assumption, and the fact that the result carries a fee-table version/date and official source URLs. Return-content detail is largely redundant with the output schema, keeping it off a 5.

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?

Dense but front-loaded: the core action and scope lead, then the guidance pointer and unit conventions, then validation behavior. Every sentence carries information, though the enumeration of rate components makes it longer than it strictly needs to be for a single-purpose tool.

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 9-parameter calculator with full schema coverage, annotations, and an output schema, the description supplies everything else an agent needs: category-id sourcing, percent/cent conventions, tax-vs-income caveat, optional-surcharge mechanics, and strict-validation expectations. No material gap remains.

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 baseline is 3, but the description adds cross-parameter semantics the schema only implies: that the final value fee applies to item + shipping + sales tax, that fee tiers apply per item while the per-order fee applies once, and that *_pct arguments are plain percents (8.25 = 8.25%) with money in whole cents. That is meaningful disambiguation beyond the field-level descriptions.

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 (calculate eBay.com US seller fees) plus the exact scope: one order, tiered per item, no paid Store subscription. The fee components listed (final value fee, per-order fee, Promoted Listings, international, seller-performance surcharge, insertion fee) let an agent distinguish this cleanly from ebay_profit and ebay_target_price without opening a 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 routes the agent to list_ebay_categories for category ids and states the eligibility condition (sellers without a paid Store subscription). It does not, however, say when to prefer this over sibling tools like ebay_profit or ebay_target_price, so the alternative-selection guidance is partial rather than complete.

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