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

Beyond the annotations, it discloses that results are point-in-time observations of live chain state that may change between calls, which explains the idempotentHint=false setting, and it enumerates negative capability boundaries (no solvency, ownership, or transaction-safety judgment). This is exactly the extra context annotations cannot 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 core action and scope, then usage routing and exclusions; every sentence carries distinct information with no filler. The do-not-use list adds the historical-balance exclusion that the schema cannot express.

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 read-only, three-parameter lookup with a full output schema and complete annotation coverage, nothing an agent needs to call it correctly is missing. Response format is intentionally left to the output schema.

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%, including the 20-item cap, address pattern, and chain enum, so the schema carries the parameter burden. The description adds only the semantic distinction that ETH is always returned while the token list is optional, which is marginal beyond what the schema already states.

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?

Names a specific verb and resource (retrieve native ETH balance for an EVM wallet), states the supported chains, and clarifies the optional expansion to up to 20 ERC-20 contracts. It also explicitly bounds the scope (no ownership, solvency, or safety evaluation), which separates it from the decision-oriented siblings.

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?

Provides explicit USE WHEN and DO NOT USE WHEN sections and names the sibling tools to route to instead (evm_transaction_hash_lookup, evm_gas_price_lookup) plus the excluded cases of historical balances and execution decisions. An agent can select or reject this tool without any inference.

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