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

Annotations already declare readOnly/idempotent/non-destructive/openWorld, so the safety profile is covered structurally. The description adds genuinely new context: it is free, requires no wallet or payment, takes no arguments, and returns a sample shape rather than the full brief. Only minor gap is not stating how the sample differs in size/coverage from the paid response.

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-loaded with the [FREE] marker, then purpose, then buy/skip routing in three compact sentences. No filler and no repetition of the title or schema.

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 zero-param preview with no output schema, the description covers what it returns (a sample shape), what it costs (nothing), and how it relates to the paid sibling. Slightly short of complete because it doesn't say how representative or truncated the sample is.

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-parameter tool, which sets a baseline of 4, and the description confirms it explicitly with "no arguments needed" and "no wallet, no payment" — aligning with the empty schema rather than contradicting it.

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 specifically that this is a free sample response for signal_day, letting the agent see the response shape before paying. It distinguishes itself from signal_day (paid, full brief), signal_latest (most recent edition), and signal_history (multi-day) by name.

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 an explicit when-to-use ("Buy signal_day when you want the full brief stored for one date") and when-to-skip with named alternatives for both the recency case (signal_latest) and the multi-day case (signal_history). Nothing is left to inference.

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