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

With no annotations supplied, the description carries the full burden and does well: it discloses the return fields (number, hash, time, tx count, base fee), the supported chains, the default chain, and even the per-call cost ($0.001 USDC). It omits edge behavior such as what happens if both number and timestamp are passed, or what an invalid block number returns.

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 compact sentences with the primary action first, then return shape, then chain/cost facts. No filler, and each clause (timestamp formats, default chain, price) carries information an agent needs.

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?

For a 3-parameter, annotation-free tool with no output schema, the definition covers what it does, what it returns, which chains work, and what it costs. It is nearly complete; only the precedence rules when both lookup modes are supplied are left to inference.

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 0%, so the description must compensate and largely does: it explains that 'number' accepts latest/finalized in addition to a block number, that 'timestamp' accepts unix or ISO formats, and that 'chain' defaults to base. The enum already enumerates the chains, but the default value is only available from the description.

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?

The description uses a specific verb (fetch) and resource (block) and immediately splits the capability into its two modes: block lookup by number/latest/finalized, and timestamp-based historical lookup. No sibling tool in the list performs block retrieval, so an agent can route to it unambiguously.

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?

It states the selection condition between the two modes ('by number/latest/finalized' vs 'last block at or before a timestamp ... for historical queries'), which is the key routing decision. It stops short of naming explicit exclusions or pointing to alternative tools (e.g. gas_fees, tx_status) when those are the better fit.

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