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

Annotations only say readOnly and openWorld; the description adds what an agent actually cannot infer: the data source (public listing schema.org), the two fields deliberately absent, and a full cost model — $0.002 USDC per successful call via x402 on Base/Solana/Arc, with failed calls uncharged. Cost and billing-failure semantics are exactly the kind of behavioral context annotations cannot express.

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 and returned fields are front-loaded in the first clause, data limits follow immediately, and pricing closes the description. No sentence is redundant; the pricing sentence earns its place because it affects whether an agent should call this at all.

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 one-parameter read-only lookup with an output schema, the description covers everything left open: source of truth, field inventory, known gaps, and billing behavior. Nothing an agent needs to decide or invoke correctly is missing.

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 the schema already documents the single 'app' parameter and gives an example. The description still adds meaning by defining the handle operationally as 'the part after apps.shopify.com/', which disambiguates slug from display name or app ID — a small but genuine increment over the schema.

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+resource: retrieves a Shopify App Store listing by app handle, and enumerates exactly which fields come back (name, developer brand, category, description, rating average and count). The 'apps.shopify.com/' anchor plus the schema.org source make it unmistakable versus the sibling store listings (dev_apple_app_store_iphone, dev_google_play_store, dev_producthunt).

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?

Gives clear framing for when this applies (you have a Shopify app slug and want listing metadata) and sets expectations with 'No install counts or prices.' It does not, however, route the agent to alternatives for other app ecosystems or point to a different tool if install/download figures are needed — the exclusions describe data gaps rather than when-not-to-use.

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