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

Annotations carry the safety profile, so the bar is lower, and the description still adds real operational context: pricing ('$0.001 in USDC on Base per successful call') and the payment protocol (x402). It does not explain pagination or failure/error behavior, and it is silent on the fact that readOnlyHint=false sits oddly against a pure retrieval call.

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?

Three tight sentences, front-loaded with the resource and the returned fields before usage and cost. Dense but every clause carries information; nothing is redundant.

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 enumerating the returned fields, and it documents the payment requirement, which is essential for a paid endpoint. For a zero-required-parameter read tool this is complete enough to call 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 description coverage is 100% for the single 'number' parameter, so the schema already documents the accepted value and the 'latest' default, and the description only echoes 'by number, or the latest one'. Baseline 3 is appropriate since the description adds no format or edge-case detail beyond 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?

Names a specific verb+resource ('A block on Ethereum by number, or the latest one') and enumerates exactly what is returned (hash, timestamp, tx count, gas used/limit, base fee, producer address). This clearly distinguishes it from siblings like eth_tx, eth_receipt and eth_gas without needing to open 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?

'Use for timestamps, confirmations and chain-activity checks' gives concrete use cases, which is stronger than implied usage. It stops short of naming alternatives or exclusions — e.g. it never says to use eth_gas/eth_tx instead when the agent wants gas price or transaction detail.

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