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

Annotations cover read-only/idempotent/non-destructive, and the description adds real context beyond them: it is free, requires no wallet, no payment, and no arguments. Auth/payment prerequisites are exactly the kind of behavior an agent needs and the annotations do not supply.

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?

One compact sentence, front-loaded with the [FREE] marker and the key precondition (no wallet/payment). Minor redundancy between '[FREE]' and 'before paying', but nothing bloats it.

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-argument preview tool with no output schema, the description covers the essential facts: free, no auth, no params, sample of signal_history. It stops short of hinting at what the sample data looks like, but nothing needed to invoke 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 baseline is 4. The description confirms 'no arguments needed', which matches the empty schema and prevents an agent from hunting for required inputs.

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 the verb+resource clearly (a sample/free variant of signal_history) and distinguishes itself from its paid sibling signal_history by explicitly framing itself as a preview of the response shape. It does not explain what the archive content actually is, but the preview-vs-paid distinction is unambiguous.

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 clear context: use it to see the shape before paying 0.1 USDC, with no wallet or payment required. It does not explicitly name signal_history as the alternative to call after previewing, but the 'before paying' framing implies the when-to-use condition well enough.

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