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

Annotations already declare readOnlyHint and openWorldHint, so the safety profile is covered. The description goes beyond them by disclosing the return shape (raw plus human-readable, symbol/decimals resolved) and, importantly, that each call costs $0.002 USDC via x402 — a real operational constraint. It stops short of explaining payment mechanics or failure behavior when payment or the token lookup fails.

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?

Two tight sentences, with the core capability front-loaded and the cost constraint appended. No filler or restatement of the tool name.

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?

No output schema exists, but the description compensates by describing what is returned (raw and human-readable balance with symbol/decimals). For a 2-parameter read tool this is nearly complete; only payment flow and edge-case behavior (non-ERC-20 contract, unverified token) are unaddressed.

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%, so both parameters are already documented as a Base ERC-20 contract and a 0x-prefixed Base address. The phrase 'any address for any token on Base' reinforces the domain but adds no format or validation detail beyond the schema. Baseline 3 applies.

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 a specific verb+resource: returns the ERC-20 balance of any address for any token on Base, with symbol and decimals applied. That is unambiguous and distinct from siblings like base_token or base_transfers, though it never explicitly contrasts itself with them.

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?

Usage is only implied: an agent infers it should call this when it needs a token balance. There is no explicit when-to-use/when-not guidance and no routing to alternatives such as base_token for token metadata. The cost line does add practical context for deciding whether to call it.

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