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

Annotations already declare readOnly, idempotent, non-destructive, and open-world, so safety is covered. The description adds genuine behavioral detail beyond that: the deterministic selection order and the tie-break policy, plus the concrete REST route, which reassures an agent about repeatability. No mention of rate limits or error behavior for out-of-range timestamps.

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 core rule is the very first sentence, with the doc link and REST route demoted to secondary lines. Every element earns its place and nothing is padded.

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?

A single-parameter read tool with an output schema and full annotation coverage needs only the selection semantics to be callable correctly, and those are stated exactly. Return values need not be described because the output schema supplies them.

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 reported at 0%, so the description must carry the load; it does reinforce that the input is a UNIX timestamp and clarifies the inclusive boundary semantics ('at or before'). However, it doesn't restate the unit (seconds) or the non-negative bound, which live only in the schema's $defs, so it only partially compensates.

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 gives a precise verb+resource ('Find the block') and then fully specifies the selection rule: greatest header timestamp at or before the input, earliest height on ties. That level of specificity clearly separates it from height-based siblings such as get_block, get_block_hash_by_height, and get_blocks_from_height.

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 'at or before' plus tie-breaking rule tells an agent exactly which query shape this tool answers, which implicitly excludes height- or hash-addressed lookups handled by siblings. It stops short of naming an alternative tool or stating exclusions explicitly, so it lands at a clear-context 4 rather than a full 5.

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