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

Annotations already declare readOnly/idempotent/non-destructive/openWorld, so safety is covered. The description adds genuinely useful non-annotation facts: it is free, requires no wallet and no payment, and takes no arguments — critical context in a pay-per-call family where cost is the main decision factor.

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?

Front-loads the [FREE] marker and the core purpose, then layers routing guidance. It is a single dense paragraph with some parenthetical nesting, but every clause carries routing or cost information rather than filler.

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?

No output schema exists, but the description explains that the tool returns a sample of signal_delta's response so the shape is visible before purchase, which is the essential expectation to set. Nothing needed to invoke a zero-argument preview is missing.

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?

Zero parameters, so the baseline is 4. The description reinforces this with 'no arguments needed,' which prevents an agent from hunting for a required date parameter that does not exist.

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 and resource — a free sample response of signal_delta's 'change list' output — and immediately names the siblings it differs from (signal_delta, signal_latest, signal_history). An agent can distinguish this preview from the other signal_* tools without opening a schema.

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 explicit routing: use signal_delta when you already hold a dated brief, use signal_latest when you hold none, use signal_history for full briefs. The when-not conditions describe the paid family rather than the preview itself, but the implied trigger for this tool (see the shape before paying) is clear.

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