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

With annotations present, the description goes well beyond them: it discloses 400 rejection with no charge for malformed addresses, pricing ($0.003/call, first 25 free, failed calls free), payment paths (x402 USDC or card key), and explicitly reconciles the readOnlyHint=false annotation ('not marked read-only because each call is charged').

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 core action and scope, then usage, then pricing/error caveats. Dense but every clause carries information (direction, counterparty, amount, count, charge policy) 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?

With no output schema, the description still outlines the return shape (direction, counterparty, amount, transaction, newest first, max 50) and covers errors, pricing, and network scope. An agent has everything needed to call it correctly.

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 all three parameters (address, token, blocks) are already documented, including the USDC default and the 1-2000 block range. The description largely restates those defaults, adding only marginal framing rather than new syntactic or semantic detail, 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?

The description states a specific verb and resource ('List a wallet's recent transfers of one ERC-20 token ... on Base') with scope details (in/out, block window, newest first, up to 50). It explicitly distinguishes itself from the sibling base_token_balance by naming the alternative for current-balance queries.

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?

It gives concrete use cases ('confirm a payment arrived or see what was sent') and names the alternative tool with the condition that selects it ('for the current balance use base_token_balance'). Nothing about when to pick this over siblings 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.