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

Annotations declare readOnlyHint=false, idempotentHint=false and openWorldHint=true; the description goes beyond them by reconciling the surprising non-read-only flag ('reads or computes only; not marked read-only because each call is charged'), and adds cost behavior ($0.003/call, x402 USDC or card key, first 25 free, failed calls free). That is exactly the kind of context annotations cannot express.

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 returned values, then usage, then the alternative tool, then pricing. Every sentence carries decision-relevant information (outputs, when to call, sibling routing, cost), with no filler.

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?

There is no output schema, so the description must convey returns and does so precisely (gas price, base fee, priority fee in gwei, transfer cost). Combined with the explicit usage, sibling routing, and pricing disclosures, nothing needed to call this 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 baseline is 4; the description confirms 'Takes no input,' matching the empty schema. There is no parameter syntax to add meaning to.

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 and resource (current gas on Polygon PoS) and enumerates exactly what is returned: gas price, base fee, suggested priority fee in gwei, and a 21,000-gas POL transfer cost. It explicitly routes the sibling case ('for the fee a past transaction actually paid use polygon_receipt'), so an agent can distinguish it from polygon_receipt without opening a 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 ('before sending a transaction or to decide whether to wait') and names the alternative plus the condition that selects it (polygon_receipt for historical paid fees). 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.