Type text into the focused input field on a cloud Android device; the call fails if no field is focused, so tap a field first.
Type text into the currently focused field on the device. The field must be focused first (tap it) — the call fails honestly when nothing is focused, instead of typing into the void.
| Name | Required | Description | Default |
|---|---|---|---|
| text | Yes | ||
| device | No |
Changes observed during successful MCP inspections.
Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
With no annotations, the description carries the full burden, and it does disclose a genuine behavioral trait: the call fails when nothing is focused rather than typing into the void. That said, it says nothing about default device selection, whether text appends or replaces, or how the failure surfaces to the caller.
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 action and the precondition. The phrase 'instead of typing into the void' is colorful but it earns its place by explaining the fail-fast behavior, so there is little waste.
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 an interaction tool with no annotations and no output schema, the description covers the action and one failure mode but omits device targeting, expected return, and behavior on unfocused fields beyond the failure note. Adequate but with clear gaps.
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 0% for two parameters, so the description must compensate — but it never mentions the optional `device` parameter at all, leaving its meaning and default entirely undocumented. Only `text` is implicitly covered.
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 (type) and resource (text into the currently focused field on the device), and the focus requirement cleanly separates it from siblings like previewapk_tap_text and previewapk_press_key.
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?
Gives an explicit precondition — the field must be focused first (tap it) — which implicitly routes the agent to previewapk_tap before calling this. It does not name alternatives or state when not to use it, so it falls short of a 5.
Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.