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

Annotations already declare readOnly, idempotent, openWorld, non-destructive. The description adds genuinely new context: no wallet, no payment, no arguments — auth and cost behavior not captured by annotations. What it does not clarify is the fidelity of the sample (truncated vs. representative), which is the main behavioral unknown 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?

Two sentences, both earning their place, with the [FREE] marker and no-payment constraint front-loaded. No redundancy.

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 tool with no output schema, the critical missing piece is what the sample actually contains and how faithful it is to the paid response. The description gestures at 'the shape' but gives no detail, leaving the agent to call blind on whether the data is usable.

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 baseline is 4. The description reinforces this with 'no arguments needed', confirming the agent should call it bare.

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 clearly that it returns a sample response of edgar_company_facts, tying it directly to the sibling paid tool. The resource is identified by the title (SEC EDGAR XBRL company facts); the description itself is about the preview mechanism rather than the data content, so it falls just short of a self-contained 5.

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?

Explicitly frames the use case: 'see the shape before paying 0.02 USDC'. This tells the agent when to reach for the preview rather than the paid call. It does not spell out the inverse (use edgar_company_facts when you need actual data), but that is strongly implied.

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