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

Annotations already declare readOnly, idempotent, non-destructive, openWorld. The description adds real behavioral context beyond that: the archive-node requirement and the error it produces, plus the coinbase-maturity caveat that rewards are counted in the balance but unspendable for 100 blocks. These are non-obvious traits an agent would otherwise miss.

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, front-loaded with what is returned and the block scoping, then caveats. Dense but every clause carries information; only the maturity note is slightly tangential to invocation.

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 tool with no output schema, the description usefully enumerates the return values (balance in wei and LAX, nonce) and covers the key failure mode (archive node). Nothing critical to calling 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 both parameters are already documented, including block accepting number/hash/latest. The description reinforces that block accepts a number or hash and defaults to latest but adds no format or syntax beyond the schema, so baseline 3 is appropriate.

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+resource: it returns the LAX balance (in wei and LAX) and nonce of an address, at a given block. Scope is precise enough that an agent knows exactly what it gets back. It does not explicitly contrast itself with siblings like explorer_address or explorer_token_balances, which keeps it from a 5.

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 implies when the tool applies (latest block vs a specific block number/hash) and warns about the archive-node prerequisite for old blocks, but never names an alternative tool or a when-not-to-use condition. Usage is contextual rather than directive.

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