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

No annotations are provided, so the description carries the full behavioral burden. It usefully discloses that only the header and transaction hashes are returned (not full transactions) and names the underlying RPC methods, but says nothing about error handling, finality implications of the tags, or return format.

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?

A single dense sentence that front-loads the action and resource, then packs the accepted selectors and RPC mapping without any wasted words.

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 no-output-schema, no-annotation read tool, the description covers what is fetched and the selector options well. The remaining gap is input-structure guidance for the nested required payload, which the 0%-covered schema leaves undocumented.

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. It does add value by enumerating valid tag values (latest/earliest/safe/finalized) that the untyped 'number' field could accept, but it does not explain the null/default semantics of the hash and number fields or how they interact inside the required payload.

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 (Fetch) and resource (Base mainnet block header and transaction hashes), plus the three input modes (number, tag, hash). It is clear on its own, but it never distinguishes itself from the sibling base_block-number, which appears to overlap heavily.

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?

The description implies when you'd reach for it (fetching block data) and lists the accepted selectors, but gives no explicit when-to-use vs when-not guidance and does not tell the agent how this differs from base_block-number or base_receipt.

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