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

Annotations already cover read-only, idempotent, and non-destructive behavior, but the description adds critical payment context: $0.001 per call, bad input refused before charge, dual invocation modes (request descriptor vs. key-backed execution), and the auth header/key purchase URL. This is exactly the kind of behavioral detail annotations cannot carry.

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?

Purpose is front-loaded in the first clause, and every sentence carries relevant information. The second sentence is dense, packing payment, auth, purchase URL, and execution modes together, which is slightly harder to scan than it could be.

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 paid API with no output schema, the description is complete enough: it explains return values (latest and pending nonce), the descriptor mode, key-backed execution mode, billing, and pre-charge validation. Nothing essential for correct invocation 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 description coverage is 100%, with the address pattern and chain enum fully documented. The description repeats the supported chains and implies the address parameter but adds no syntax or format detail beyond what the schema already provides, so baseline 3 applies.

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 exact resource (account transaction count) and the specific outputs (nonce at latest block plus pending nonce from the node's pool), and enumerates supported chains. This distinguishes it clearly from sibling EVM lookup tools like evm_transaction or evm_block.

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?

"Use when you need an account's transaction count..." gives a clear triggering condition and chain scope. However, it does not explicitly compare against alternative EVM tools or state when to prefer another sibling.

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