apps_input_targets

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

Annotations already declare readOnlyHint, idempotentHint and destructiveHint=false, so the safety profile is covered. The description adds genuinely new behavioral context: coordinates are normalized to the App viewport and are independent of the device's 150% browser zoom, plus an explicit statement that no preview launch/link/switch occurs. It omits anything about refresh/caching or how often the bindings should be re-read.

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 tight sentences with zero filler: the primary action and its timing come first, the coordinate contract second, and the negative boundary last. Every clause earns its place.

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 identifies what is returned (active preview and device App bindings) but not the shape of that payload, so an agent cannot fully anticipate the response. Annotations and the coordinate contract cover the rest, so the gap is modest rather than blocking.

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 and the baseline of 4 applies. The coordinate-normalization note is about the coordinate system the caller must use downstream, which is useful even though it is not a parameter of this call.

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 (Read) and resource (the active preview and device App bindings), and scopes it as a pre-input step. It differentiates itself from mutation siblings like apps_preview_input and apps_control by declaring it only reads bindings, though it does not explicitly contrast with apps_state, which an agent might confuse it with.

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?

"before input" gives a clear timing/context cue, and "Does not launch, link or switch the person's preview" functions as an explicit when-not boundary. It stops short of naming the sibling tool to call afterward (e.g., apps_preview_input, apps_interface_input), so routing is implied rather than spelled out.

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