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

The annotations already mark the call readOnly and non-destructive, so the description correctly does not repeat the safety story. It adds genuinely non-obvious behavior: a not-yet-existing block returns a 404 that is not charged, failed calls are free, and because each successful call bills $0.01 (first 25 free), repeats are not free – which explains the idempotentHint=false. It stops short of describing response shape or any rate limits, so a 4 rather than 5.

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?

It is front-loaded with purpose and return fields before pricing, and each sentence carries information. The billing point is slightly spread out ('charged, so repeats are not free' followed later by 'failed calls free'), which costs it a perfect score.

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?

There is no output schema, so the field list in the description does important work. Together with the 404 behavior and the billing rules, an agent has enough to call this correctly; only the exact response envelope and default-block nuance are left implicit.

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 schema already states the param is a block number or the default 'latest', so the 3 baseline applies. The description adds only the 'decimal number' phrasing and the 'number=latest' example, which are marginal gains.

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 Celo, or any block by decimal number') and enumerates exactly which fields come back (hash, timestamp, tx count, gas used/limit, base fee, producer). It clearly separates itself from the same-family sibling celo_gas, which handles fees.

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 explicit when-to-use ('timestamps and confirmation counts') and when-not / alternative ('for current fees use celo_gas'). It also gives a concrete invocation example (number=latest), so the agent doesn't have to guess the default form.

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