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

Annotations only say readOnlyHint and openWorldHint, but the description adds substantial behavioral detail: the exact cost and payTo address, accepted input formats, rejection of pending, the paid 200 with found:false behavior for unknown ids, and scope limitations. This goes well beyond what annotations convey.

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?

Every sentence carries load-bearing information: cost, resource, input formats, returned fields, error behavior, exclusions, and payTo address. The description is tightly packed and front-loaded with the most important facts.

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?

Given there is no output schema, the description usefully lists the returned fields and covers edge behavior such as unknown ids and rejected pending values. The only meaningful gap is the ambiguous 'hash=' construction and the lack of a concrete example, which leaves minor room for misinterpretation.

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% with basic descriptions, and the description adds valuable parameter semantics by enumerating accepted n formats (latest|earliest|safe|finalized, decimal, 0x number, hash=) and noting 'Rejects pending.' The phrase 'hash=' is slightly ambiguous relative to the separate hash parameter, which prevents a perfect score.

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 as 'block header via public RPC' and lists the returned fields, so an agent knows what the tool provides. However, it lacks an explicit verb like 'fetch' or 'get', and while 'No full txs' and 'Not a mempool tip' help distinguish it from siblings, no alternative tool is named.

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 gives clear context for when the tool is appropriate: it fetches block headers, accepts specific block tags, and explicitly states exclusions: 'Rejects pending', 'No full txs', and 'Not a mempool tip'. It stops short of explicitly naming sibling tools to use instead, which keeps it from a 5.

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