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

Unusually strong: it explains WHY the unusual annotations (readOnlyHint=false, idempotentHint=false) are set – repeated calls cost $0.001 via x402/credits, so retries are non-idempotent. It also discloses 404-unpaid and never-charge-on-failure semantics. This is exactly the kind of context annotations cannot convey; no output schema exists, so return values are covered by the description's field list.

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?

Purpose and the base_gas alternative are front-loaded; the payment mechanics run long but each clause explains a real behavioral trait (pricing, charge-on-repeat, no charge on failure). Slightly dense, but nothing extraneous enough to cut.

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?

Given a single optional parameter, no output schema, and annotations that invert the usual safety hints, the description covers return fields, error behavior, cost, and payment rails. An agent has everything needed to call it correctly and to reason about retry cost.

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 the baseline is 3, but the description adds the 'decimal number' format hint and clarifies omission yields the latest block, supplementing the schema's terse 'Block number, or latest (default)'.

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 (fetch) and resource (a block on Base) with the exact returned fields enumerated, and explicitly differentiates itself from the sibling base_gas. An agent can distinguish it from base_receipt/base_gas without opening any 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?

Gives positive usage guidance ('use for timestamps and confirmation counts') and names the alternative for the adjacent need ('for current fees use base_gas'). It also covers the error case (nonexistent block returns 404, uncharged), so the agent knows how to react too.

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