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

Annotations already declare readOnly/idempotent/non-destructive, yet the description still adds real value: it is public, needs no sign-in, explicitly does not expose private stock/sales/orders, and specifies that missing, unknown, inactive or private stores produce a tool error with private details remaining hidden. That error-behavior disclosure is exactly the kind of thing annotations cannot carry.

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-loaded with purpose and trigger, then behavior, then error contract — a sensible ordering with no filler. Minor deduction because 'Read-only; no store settings or inventory changes' partly restates the readOnlyHint annotation, though it does add a plain-language gloss.

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, the description supplies the return contract itself ('Returns the canonical public storefront URL as text'), plus the failure modes. For a single-parameter public lookup that is everything an agent needs before calling it.

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 the schema already says 'Seller storefront username from a SuperCatch store URL.' The description's 'from its URL username' and 'username or storefront URL' restate the same meaning rather than adding format, case-sensitivity, or paste-the-URL-in-full guidance, 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?

Specific verb plus resource plus scope: 'Find one public seller storefront from its URL username.' The word 'public' plus 'no sign-in required' separates it from the numerous authenticated store-side siblings (get_store_inventory, list_store_listings, list_store_orders), so an agent can pick it without opening the 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?

Explicit positive trigger: 'Use when the seller's username or storefront URL is already known,' which also implies it is the wrong tool for discovery-only queries. It does not name a sibling alternative (e.g. search_marketplace) by name, so the when-not half is only implicit.

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