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

With no annotations, the description carries the full burden. It usefully discloses that only arm64-v8a/universal APKs are accepted and that only the needed splits are auto-selected from bundles, but it says nothing about whether the call blocks until install completes, what happens to existing app data on an update, or how incompatible ABIs surface as errors.

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?

A single dense sentence, front-loaded with the action and resource, followed by compatibility constraints and then the follow-up call. No filler or redundant restatement of the tool name.

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 three-parameter tool with full schema coverage and no output schema, the description covers the key external facts: accepted formats, ABI constraint, split behavior, and the next step. The remaining gap is failure/blocking behavior on incompatible artifacts, which an agent would benefit from knowing.

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 baseline is 3. The description adds some meaning by clarifying that `url` must be a public direct download and by explaining the split-selection behavior tied to `phone_id`, but it never mentions `grant_permissions`, leaving that entirely to 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 and resource ('Install or update an app') plus the exact input form ('public download URL') and supported artifact types (APK arm64-v8a/universal, .apks/.xapk). This clearly separates it from list_apps and uninstall_app among the siblings.

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?

Covers both install and update cases and routes the agent to the next step by naming `act` with `{"type":"open_app","package":…}`, which is genuine alternative/sequencing guidance. It stops short of stating when not to use it (e.g. sideloading local files, downgrades) or any prerequisites.

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