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

Annotations already cover read-only, open-world, non-idempotent and non-destructive, but the description adds real behavioral detail beyond them: 404 and uncharged for not-yet-existing blocks, failed calls free, and per-call billing that makes repeats non-free. Pricing and failure semantics are the kind of context annotations cannot express.

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?

Dense but front-loaded: the resource, returned fields, alternative tool, and error behavior come before the pricing tail. The billing sentence is somewhat repetitive ('each call is charged, so repeats are not free' restates the price) but remains operationally relevant.

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 compensates by listing exactly what a block response contains (hash, timestamp, tx count, gas used/limit, base fee in gwei, producer) and covers the missing-block case and default parameter, which is everything needed 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 'number' parameter is already documented with its 'latest' default, so the description only reinforces the default via the example 'number=latest'. Useful but largely duplicative of the schema.

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 ('Latest block number and block details on Base, or any block by decimal number') and enumerates the returned fields, so it is clearly distinguishable from siblings like base_tx or base_gas.

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?

Explicitly names intended uses ('timestamps and confirmation counts') and names the alternative tool for the adjacent need ('for current fees use base_gas'), giving both when-to-use and when-not-to-use guidance.

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