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

Annotations already declare readOnlyHint=true, destructiveHint=false, openWorldHint=true, idempotentHint=false; the description is consistent with all of them ('Reads or computes only and changes nothing'). It adds behavior the annotations cannot express: 422 with revert reason on failure, failed calls are free, cost is $0.01/call via x402 USDC or a card key, first 25 free, and repeats are billed again (consistent with idempotentHint=false). This is materially useful billing and failure semantics.

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 outcome, then inputs, then usage, then cost/error behavior — good ordering with an inline example. It is dense and the pricing/payment sentence is long, but nearly every clause carries decision-relevant information; only the 'Price $0.01/call via x402 USDC or a card key (/credits)' detail is slightly over-explained.

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, and the description compensates by naming the return units (gas units, gwei, CELO) and the error shape (422 + reason). For a 4-parameter read-only estimator with a single required field, nothing an agent needs in order to call it correctly — inputs, cost, failure mode, non-mutation guarantee — 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?

Schema coverage is 100%, so the baseline is 3; the description does add a little beyond the schema by grouping the inputs and explaining that `from` matters only 'when the call depends on it', which qualifies the schema's terse 'default: an empty address'. Units ('value in CELO') duplicate the schema, so the gain is modest rather than substantial.

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 ('Estimate the gas a transaction would use on Celo') plus the underlying RPC method (eth_estimateGas) and the exact outputs returned (gas units, gwei, CELO). It explicitly names the sibling it is not ('for the gas price alone use celo_gas'), so an agent can route between the two without opening either 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 triggers ('Use before sending a transaction or to price a batch') and an explicit alternative ('for the gas price alone use celo_gas'). It also states the failure condition and its consequence ('A transaction that would revert is 422 with the reason, uncharged'), which is exactly the guidance an agent needs before committing to a call.

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