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

Annotations already declare readOnlyHint=true and idempotentHint=true, so the safety profile is covered. The description adds the concrete list of returned header fields and the 'latest or specified' behavior, but does not disclose anything beyond that, such as response structure or potential edge cases.

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?

The description is a single, dense sentence that front-loads the core purpose and result fields, then adds the key usage hint. There is no filler or redundant restatement of the tool name.

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 read-only, one-parameter tool with annotations and an output schema present, the description is largely sufficient. The only minor gap is that it does not explicitly orient the agent toward when a 'specified' block is preferable to 'latest', but the schema and output schema carry most of that burden.

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?

The input schema already documents the single 'block' parameter with 100% coverage, including hex/decimal/tag formats and the default value. The description only restates 'latest (or specified)' and does not add meaningful parameter semantics beyond what the schema provides.

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 clearly identifies the resource (Base block header) and the information returned (number, timestamp, transaction count, base fee), making it easy to understand what the tool does. It does not explicitly contrast itself with siblings like tx_activity or crypto_ticker, but the specific resource and fields are enough to distinguish it in most cases.

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 phrase 'Preflighted before payment' gives a concrete usage context: this tool is intended for checking block state ahead of payment actions. It does not explicitly state when not to use it or name alternatives, so it stops short of full routing guidance.

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