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

Annotations already declare readOnlyHint=true and destructiveHint=false, so the safety profile is covered. The description adds genuinely new behavior: the tool fails with store_unreachable when the marketplace is unreachable and 'nothing is guessed', which tells the agent to treat an error as a hard failure rather than a partial/empty result. It does not describe result ordering or any caching/refresh behavior.

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?

Two short sentences, front-loaded with the purpose and followed by the failure mode and sibling pointer. No filler; the parenthetical '(nothing is guessed)' earns its place by clarifying error semantics, though the phrase is slightly informal.

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 compensates by enumerating the returned fields and the error name. Combined with annotations, an agent has enough to call it and interpret failure. Only minor gaps remain, such as whether the list can be empty versus unreachable.

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?

The tool takes zero parameters, so there is nothing for the description to disambiguate beyond the schema. Baseline 4 applies; the mention of returned fields is a bonus rather than a parameter explanation.

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 ('List the apps in the phone's Store') and qualifies the scope as 'marketplace apps from the control plane', which separates it from installed-app listings. It also enumerates the returned fields (id, name, bundle url, version), so an agent knows exactly what this yields. It does not name the rival siblings list_apps or list_installed_apps explicitly, so it stops just short of a 5.

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?

'Install one with install_app' hands the agent the natural next step and implicitly defines the boundary between browsing and installing. There is no explicit when-not-to-use clause or prerequisite note, but for a zero-argument read tool the usage context is clear.

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