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

Annotations already cover safety (readOnly, idempotent, non-destructive), so the description's job is to add context — and it does: it discloses a paywall/quota model (3 free directory screenshots, remainder requires Library Pro at $19/mo) and that live lookups require an API key. It does not mention rate limits or response shape, but this is a strong add beyond the annotations.

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?

Four short sentences, front-loaded with the core action and mode distinction. The pricing detail earns its place as it drives the free/paid decision, though the listing cost sentence is slightly verbose.

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 6-parameter, no-output-schema tool it covers modes, auth, and quota, but leaves a notable gap: nothing tells the agent which of the four identifiers (slug/query/app_id/app_url) to supply or whether they can be combined. That ambiguity matters for 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 83%, so the baseline is 3. The description reinforces the meaning of live=true and explains that query searches the directory and then the App Store, but it does not clarify the relationship between slug, query, app_id, and app_url (mutual exclusivity, precedence) which is the main ambiguity across 6 params.

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?

The description states a specific verb and resource ('Fetch high-resolution App Store screenshots') and distinguishes the two operating modes (directory shots vs. live lookup). It names one sibling (get_directory_app) but does not differentiate from get_directory_screens or get_app_videos, which overlap in subject matter.

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?

It gives explicit conditions: pass live=true when you want the user's own app's current listing, and use get_directory_app when you already have a catalog slug. That is real routing guidance, though it never states when to prefer this tool over get_directory_screens.

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