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

Annotations already declare readOnlyHint, idempotentHint, destructiveHint=false and openWorldHint, so the safety profile is covered. The description adds genuinely new behavioral context: it costs nothing, requires no wallet or payment, and takes no inputs — the key operational facts an agent needs before calling.

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?

A single tight sentence with the '[FREE]' marker and the sibling it previews front-loaded, followed by the zero-friction facts. No filler, no repetition of the title.

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?

There is no output schema, but the description explicitly frames the return as a sample response whose purpose is to reveal the shape, which is the relevant expectation-setting an agent needs. It is complete for a zero-argument, zero-cost preview 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?

The tool takes zero parameters, which is the baseline-4 case, and the description reinforces this by stating 'no arguments needed' so the agent knows not to supply any. Nothing further is required.

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 resource (a sample response for signal_continuity) and explicitly distinguishes it from the paid sibling, with the free/preview nature front-loaded. An agent can tell immediately this is the no-cost sample path rather than the production signal_continuity call.

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?

Communicates when to use it ('see the shape before paying') and what it requires (no wallet, no payment, no arguments). It does not explicitly state the inverse condition — that paid signal_continuity should be used for real data — but that is strongly implied and the sibling name is given.

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