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

Beyond the readOnlyHint annotation, the description discloses a real behavioral trait: the two-step payment handshake where the first call returns only payment terms and must be retried with a signed payment. It also supplies the measured output shape, so the agent knows what a successful response looks like. This is substantive context the annotations do not carry.

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 purpose and the chain before any operational detail, which is the right ordering. The HTTP URL and payment paragraphs read as templated boilerplate and could be trimmed, but the measured-output line earns its place given there is no output schema.

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 description carries the return-value burden and discharges it via the 'Measured output' example. It also covers the payment requirement and the exact parameter. Only error/failure responses and rate-limit behavior 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% and the single 'address' parameter is already documented as '0x + 40 hex'. The description merely repeats that same constraint verbatim, adding no syntax, validation, or example beyond the schema. Baseline 3 is the correct ceiling here.

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 native ETH balance of a Base address via eth_getBalance') and the exact network, which cleanly separates it from the gnosis_eth_getbalance and eth_mainnet_eth_getbalance siblings. An agent can identify both the operation and the chain without opening the schema.

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?

The description gives operational guidance for the x402 flow ('Call once with no payment... Retry the same call with the signed payment at _meta["x402/payment"]'), which is useful invocation context. However it never states when to prefer this tool over chain alternatives (Gnosis, Ethereum mainnet), leaving selection entirely to the name. Adequate but with a clear gap in alternative routing.

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