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

Discloses useful behavioral context beyond the annotations: non-existent blocks return 404 and are uncharged, the billing model (price, free tier, failed calls free), and it explicitly reconciles the readOnlyHint=false annotation by explaining it is a billing artifact, not a data mutation. It also states the tool reads/computes only.

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?

Front-loaded with purpose, then usage, edge cases, billing, and the annotation caveat. Sentences are information-dense with no filler; relative to the sibling set the sizing is well matched.

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?

No output schema exists, so the description carries the burden and does so: it lists returned fields, covers the error/edge case, states cost, and heads off the readOnlyHint misinterpretation. Complete for an agent 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%, so the baseline is 3. The description adds format detail ('decimal number'), confirms 'latest' is used when omitted, and supplies the example number=latest, adding modest value beyond the schema entry.

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 ('Fetch a block on Ethereum by decimal number, or the latest one when omitted') and enumerates the returned fields, so the agent knows exactly what this returns and how it differs from eth_gas and other eth_* siblings.

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 ('for timestamps and confirmation counts') and names the alternative with its selecting condition ('for current fees use eth_gas'). Nothing is left to inference.

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