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

Annotations already declare readOnlyHint, idempotentHint, openWorldHint and non-destructive, so the safety profile is covered. The description adds real behavioral context beyond that: the directory path requires no API key, the live lookup requires one, and directory results include markdown images. It does not discuss pagination or rate limits, keeping it short of 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?

Four tight sentences, front-loaded with purpose, followed by behavior and routing. Every sentence earns its place with no filler, though the routing sentence could be marginally tighter.

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, 0-required, read-only lookup with no output schema, the description covers the source-selection logic, the API key requirement, and the return format (curated listing shots with markdown images). It is nearly complete; only edge cases like missing-directory handling are unstated.

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 description coverage is 83%, so the schema already documents most parameters, and the description largely restates the live/slug behavior rather than adding syntax or format details. Baseline 3 is appropriate given the schema does the heavy lifting.

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 opens with a specific verb+resource ("Fetch high-resolution App Store screenshots") and clearly distinguishes itself from siblings by naming get_directory_app as the alternative when a catalog slug is already available. An agent can tell what this does 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?

It explicitly states when to use this tool ("for the user's own app") versus the sibling ("use get_directory_app when you already have a catalog slug"), and documents the branching behavior (directory-first, live fallback, live=true to skip). Routing conditions are fully specified.

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