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

Annotations already declare readOnlyHint=true, destructiveHint=false and openWorldHint=true, so the safety profile is covered. The description still adds real value beyond them: the 404-for-nonexistent-block behavior, the fact that failed calls are free, and the charging model that explains why repeats are not free (consistent with idempotentHint=false). It does not contradict any annotation, but the pricing/monetization block is commercial rather than behavioral detail about the call itself.

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?

Information is front-loaded: purpose and returned fields come first, the sibling routing second, and pricing last. Most sentences earn their place for an agent that must reason about cost, though the x402 USDC / card key / first-25-free clause is dense and partially redundant with the later 'failed calls free' statement.

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 description carries the burden of describing the response, and it does so field by field (hash, timestamp, tx count, gas used and limit, base fee in gwei, producer). Combined with the 404 behavior, the example call, and the cost model, an agent has everything needed to invoke this correctly in one pass.

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%, so the single 'number' parameter is already documented as 'Block number, or latest (default)'. The description adds a modest amount — it clarifies the number must be decimal and provides a concrete example — but does not specify any alternative formats or edge cases for the parameter beyond that.

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?

Opens with a specific verb and resource — latest block number and details on Unichain, or any block by decimal number — and then enumerates exactly what is returned (hash, timestamp, tx count, gas used/limit, base fee in gwei, producer). It also names the sibling it is not (unichain_gas) so the agent can distinguish it from unichain_block-adjacent tools 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?

Explicitly states when to use it ('timestamps and confirmation counts') and when not to ('for current fees use unichain_gas'), naming the alternative directly. It also gives the canonical invocation example (number=latest) and the edge-case condition (block that does not exist yet returns 404, uncharged), leaving little to inference.

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