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

Annotations cover the safety profile (readOnly, idempotent, non-destructive, openWorld), and the description adds genuinely useful context beyond them: no wallet, no payment, and no arguments required. The 'sample response' phrasing hints the data is illustrative rather than live, which is important behavioral context for a preview tool.

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?

A single sentence that front-loads the '[FREE]' qualifier and the sample-response purpose, with no wasted clauses. The bracketed marketing tag is slightly noisy but costs little.

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-arg preview with no output schema, the description supplies the essentials: free, no auth, no payment, and that the response is a shape preview. It doesn't enumerate the fields in the sample, but that gap is minor at this complexity level.

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, so the baseline is 4, and the description explicitly confirms 'no arguments needed', matching the empty schema and additionalProperties:false. Nothing further is required.

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+resource: it returns a sample response for gas_price (Base gas price) so the shape can be inspected before paying. It clearly distinguishes itself from the paid gas_price sibling by naming the price gate (0.002 USDC), though it never says outright that it returns static/sample data rather than live values.

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?

Usage context is clear: call this before paying for the real gas_price to preview the response shape. The paid alternative (gas_price) is referenced implicitly via the price mention, but there is no explicit 'use gas_price when you need live data' routing sentence.

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