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

Annotations already cover read-only/idempotent/open-world, and the description adds substantial context beyond them: data is read straight from each chain's RPC, chain="all" runs in parallel and filters to chains where the address has balance/txs/code, cost is $0.002 per call with 10 free/day and an x402 payment-required result, and errors return isError uncharged. This is rich operational detail an agent needs.

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 payload description, then scoping behavior, then when-to-use, then price, then error handling. Dense but every sentence carries distinct information 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?

An output schema exists so return values needn't be spelled out, and the description covers selection criteria, cost/payment path, and error semantics for what is otherwise a simple two-parameter read tool. Nothing needed to call it correctly 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 baseline is 3, but the description adds real meaning: it explains that chain="all" is parallel and returns only active chains, which is behavioral semantics the enum alone does not convey. It adds no extra detail on the address parameter, which the pattern already documents.

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 data returned (native balance with USD, tx count, contract/wallet classification, ENS name), the resource (any EVM address), and the scope (17 chains, one or all). An agent can immediately tell this apart from evm_tx, ens_resolve, or wallet_holdings without opening a 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?

Includes an explicit 'When to use' clause and names the condition that routes elsewhere ('for Solana wallets use wallet_holdings'), plus explains the chain="all" discovery scenario. It does not mention other EVM-adjacent siblings such as evm_tx or ens_resolve, so routing is clear but not exhaustive.

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