set_pin

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

With no annotations provided, the description carries full responsibility for behavioral disclosure, and it excels: it reveals the primary-device-only constraint, the failure mode on linked devices, the PIN format (4–20 digits), the use of the PIN for storage key derivation, the 7-day lockout on forget, and a warning against choosing a forgettable PIN. All significant side effects are disclosed.

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 dense but every sentence contributes: purpose, device constraint, re-registration effect, PIN format, key derivation, lockout consequence, when-to-use, and the alternative tool. It front-loads the primary purpose and flows logically from how it works to the warning. No filler or repetition.

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 one-parameter tool with no output schema, this description is fully complete. It covers what the tool does, when to use it, the only parameter, the failure scenario, side effects, and the recommendation to use remove_pin for reversal. An agent has everything needed to invoke it correctly and understand the impact.

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 input schema already fully describes the pin parameter as '4–20 digit numeric PIN', so schema coverage is 100%. The description adds value beyond that by explaining why the PIN matters (storage key derivation) and the consequence of forgetting it (7-day lockout). This is more than a repeat of the schema, though not a completely new semantic layer.

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 action (set a Signal Registration Lock PIN), the resource (the Signal account), and the purpose (protect against SIM-swap and unauthorized re-registration). It is unmistakably distinct from siblings like remove_pin and pin_message, leaving no ambiguity about what this tool does.

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?

It explicitly says 'Use when you want to harden your account against SIM-swap attacks' and points to remove_pin as the way to disable the lock. It also states a critical precondition: only works on the primary device, with a specific failure message on linked devices, so an agent knows exactly when to call it.

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