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

Annotations already cover the safety profile (readOnlyHint, destructiveHint false), and the description still adds genuinely new context: per-call pricing ($0.01 via x402 USDC or card key), 25 free calls, failed calls free, and that repeats are charged. That last point explains the idempotentHint=false annotation in practical terms, which the annotation alone does not convey.

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 purpose and the returned values, with routing and pricing trailing behind. It is dense but nearly every sentence carries information; the billing sentence is slightly packed with three distinct facts that could be split, but nothing is wasted.

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 explain return values, and it does so concretely (three gwei-denominated figures plus a transfer cost). An agent has everything needed to call it and interpret the answer; only the optional `only` parameter goes unmentioned, a minor gap for a zero-required-param read tool.

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% and the single parameter `only` is fully documented in the schema, so baseline is 3. The description actively says 'Takes no input', which glosses over the optional output-trimming parameter and could cause an agent to miss a useful optimization; it contributes nothing positive about the parameter.

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 price on zkSync Era), names the underlying call (eth_gasPrice), and enumerates exactly what comes back: gas price, base fee, suggested priority fee in gwei, and the 21,000-gas ETH transfer cost. That is far more specific than the title and lets an agent distinguish it from zksync_gas_history and zksync_receipt without reading the 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 timing guidance ('use before sending a transaction or to decide whether to wait') and names the alternative for the opposite case ('for the fee a past transaction actually paid use zksync_receipt'). The when-to-use and when-not-to-use routing is stated outright rather than inferred.

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