has_biometric_enrolled

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

No annotations are provided, so the description must carry the full burden. It discloses key behaviors: works on emulators and physical devices, the framework only exposes an enrolled count (never which finger id), and that a wrong fingerprint_touch id trips a HAL lockout after a few tries. It also advises enrolling deterministically. While it covers most behavioral traits, it does not mention whether the tool requires any special permissions or adb setup, leaving a minor gap.

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?

The description is three sentences: the first states the core function, the second provides critical usage guidance, and the third adds behavioral nuances. Every sentence serves a distinct purpose without redundancy or fluff. It is well-front-loaded and concise.

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?

Given the simplicity (1 optional parameter, no output schema, no nested objects), the description is fully adequate. It provides purpose, usage context, behavioral insights, and practical advice. There is no missing information needed for an agent to correctly select and invoke this tool.

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 100%, so the schema already documents the single optional 'serial' parameter. The description does not add additional meaning about the parameter beyond the schema. Baseline 3 is appropriate.

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 explicitly states the tool reports whether any fingerprint is enrolled and how many, from 'dumpsys fingerprint'. The verb 'Report' and resource 'biometric enrollment' are specific. It clearly distinguishes from siblings like 'fingerprint_touch' (which performs a touch) and 'finger_remove' (which removes enrollment), making its purpose unique.

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?

The description provides clear when-to-use guidance: 'Check this BEFORE a biometric flow'. It explains the consequence of not checking (fingerprint_touch can never satisfy BiometricPrompt and just sits on 'Touch the sensor') and gives explicit branching alternatives ('branch to enrolling one or to the PIN path instead of guessing'). This is exemplary usage guidance.

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