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

Annotations already cover read-only, idempotent, open-world and non-destructive. The description adds two things annotations can't: the cost ($0.001/call) and the shape of the response including the block number. That is real added value beyond the structured fields, though pagination/rate-limit behavior is unstated.

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?

One dense sentence that front-loads the resource and return shape, then tacks on cost and use case. No wasted clauses.

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 enumerates the return fields (eth, usdc, token object with address/symbol/decimals/balance, block), which covers the main completeness burden. Missing only edge-case behavior such as errors for unverified tokens or unsupported chains.

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% and both params are documented in the schema, so baseline is 3. The description only clarifies that the token param maps to an optional ERC-20 result, adding little beyond what the schema already says.

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 with scope: the Base (8453) balance of one address, covering ETH, USDC and arbitrary ERC-20s. The chain ID and enumerated assets make it unmistakable against siblings like price_for or coin_snapshot.

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?

"Use to read a Base wallet's ETH, USDC or any ERC-20 balance now" gives a positive use case, but never names an alternative (e.g. price_for for quotes vs. this for holdings) or any condition for choosing otherwise. Usage is implied rather than routed.

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