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

Annotations already mark readOnlyHint true and destructiveHint false, and the description reinforces this with 'needs no signature, never moves funds'. It also discloses the concrete JSON return shape, which adds behavioral context beyond the annotations, though it does not cover error cases or token-balance exclusions.

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?

Three sentences: purpose, return example, and practical use case. Every sentence adds a distinct and necessary piece of information, and the most important facts are front-loaded.

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 JSON example fills the gap. It covers the chain, balance, and USD value, and the 'read-only' safety note plus intended swap use case makes the tool self-contained enough for correct selection and invocation.

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?

Input schema covers both parameters in detail: the address format and chain enum are fully documented. The description adds the native-coin mapping (SOL, ETH, BNB) and the output semantics, but does not provide significant operational guidance beyond the schema itself.

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 specific verb 'Look up' and resource 'native-coin balance of any wallet address', explicitly listing Solana, Ethereum, Base, and BNB Smart Chain. The response example clarifies the exact output, and mentioning 'native-coin' distinguishes it from sibling asset-listing tools like get_assets and get_prices.

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?

Gives a clear condition: 'Useful before building a swap to verify the wallet can cover amount plus network fees.' It does not explicitly name alternatives or say when not to use it, but the native-balance framing plus the swap context provides enough directional guidance.

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