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

Annotations already declare readOnlyHint=true, but the description adds genuine behavioral context beyond that: the two-step payment negotiation flow and the exact location to attach the signed payment. It does not, however, disclose rate limits, error/retry behavior, or what constitutes a settled payment failure.

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?

The opening sentence is well front-loaded, but it is followed by an enormous raw 'Measured output' JSON blob that dominates the definition and is not structured as a readable example. The prose is reasonable; the unstructured dump is wasteful.

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 single-parameter read tool with readOnlyHint and no output schema, the description covers the payment flow and shows a concrete sample of the returned block shape, which compensates for the missing output schema. Enough to call it correctly.

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 the single 'block' parameter is already documented as 'a block number, or latest'. The description only restates this ('block number or latest') without adding format details such as hex encoding expectations, so the 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 and resource ('Base on-chain read: a block by number or latest') and names the method eth_getBlockByNumber. The chain is explicit, which distinguishes it from the eth_mainnet and gnosis siblings, though no sibling is named directly.

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 x402 payment handshake is clearly described (call once unpaid to get terms, retry with the signed payment at _meta['x402/payment']). However, there is no guidance on when to choose this Base block-read over the many alternative chain/block-read siblings - usage is only implied from the chain name.

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