prefer_pin

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

With no annotations provided, the description carries the full burden. It discloses that the tool 'tries' to move the prompt (implying possible failure), mentions two distinct mechanisms, and warns about app-controlled suppression. It advises a follow-up step. This is good behavioral context, though it could mention prerequisites or failure cases more explicitly.

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 two sentences long, each earning its place. The first sentence states the primary action, the second gives crucial post-usage guidance. No filler or repetition. Efficient and front-loaded.

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 lack of output schema and the tool's nature (a UI fallback action), the description is fairly complete. It explains what the tool does, warns about potential limitations, and tells the user the next steps (describe_ui then enter_pin). Could be strengthened by mentioning return behavior or side effects, but overall sufficient.

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% for the single optional 'serial' parameter, with a clear description in the schema. The tool description adds no additional parameter semantics, so the baseline score of 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 clearly states the tool's purpose: 'Try to move a standard BiometricPrompt to its PIN/password fallback.' It specifies the actions (selecting a system button or sending BACK) and the resource (BiometricPrompt). This distinguishes it from siblings like 'enter_pin' and 'describe_ui'.

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 context for when to use the tool and how to proceed after invocation: 'confirm the resulting PIN pad with describe_ui before calling enter_pin.' It warns that app-controlled prompts may suppress or rename the option. However, it does not explicitly state when not to use it or mention alternative tools for different scenarios.

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