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

Adds substantial context beyond annotations: cost ($0.002 USDC), failure policy (no charge on failed read), no account/API key, and the full two-step x402 payment flow including the PaymentRequired response, the params._meta['x402/payment'] retry, and the legacy base64 argument. This also explains why readOnlyHint=false despite being a read (payment is transferred), so no contradiction.

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?

The capability sentence is front-loaded and the payment block is bracketed and clearly separated. It is longer than typical, but nearly every clause (price, no-charge-on-failure, no API key, payment retry mechanics) carries decision-relevant information for the agent.

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?

Output schema exists, so return-value explanation is not required, yet the description still summarizes the returned fields (symbol, decimals, raw/formatted amount, block number). Combined with full payment-mechanics disclosure and scope limits, nothing an agent needs to call it successfully 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% and both meaningful parameters (address, tokens with max 20) are already documented in the schema. The description restates required/optional shape and adds only the constraint that named extras are not discovered beyond the listed set, which is marginal added meaning.

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?

Opens with a specific verb-and-resource statement: reads ETH, USDC, ~25 widely held Base tokens, plus up to 20 caller-named ERC-20 contracts, for any address. It also names the data source (Base mainnet RPC) and the returned fields, which clearly separates it from siblings like ontario_base-gas and ontario_base-tx-check.

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?

States prerequisites ('Required: address'), scope restrictions ('Base mainnet only'), and explicit exclusions ('no prices or USD values; tokens outside the list and your extras are not discovered'). It does not explicitly route to an alternative sibling when the exclusions apply, so it falls short of a 5.

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