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

Annotations already cover the safety profile (readOnly, idempotent, non-destructive, openWorld), so the bar is lower; the description adds behavior those annotations cannot express — that it is free, needs no wallet/payment, takes no arguments, and returns a sample shape rather than the real trace. It does not detail the sample payload, but that is minor for a preview.

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] tag and purpose in the first clause, then the buy/skip routing in two following sentences. Every sentence carries distinct information; nothing is repeated from the name or 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?

For a no-argument, no-output-schema preview tool, the description covers what it returns (a sample response shape), its pricing model, its scope, and the alternatives. Nothing an agent needs to call it correctly 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 schema carries nothing to clarify and the baseline is 4. The description correctly reinforces this by stating 'no arguments needed,' which is the only parameter-relevant fact for a no-arg tool.

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?

Names the exact operation (sample response for signal_topic_trace) and its scope (single signal id trace across every dated edition), and explicitly distinguishes itself from the signal_continuity and signal_day siblings. An agent can identify this as the free preview variant without opening any 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 when-to-use ('Buy signal_topic_trace when you follow one thread') and when-not ('Skip it when you want every thread's status at once (use signal_continuity) or a whole day's brief (signal_day)'). Both alternatives are named with the condition that selects them.

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