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

Annotations already declare openWorldHint, idempotentHint, and destructiveHint=false. The description adds genuinely useful, non-obvious context: the 0.005000 test USDC cost and the distinct payment chain (eip155:84532), which explains the readOnlyHint=false side effect. However, the idempotencyKey note largely duplicates the schema field description and no failure/rate-limit behavior is covered.

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 short sentences with the purpose front-loaded, then cost, then the retry note. Nothing is padded and every sentence is load-bearing, though the idempotency clause is somewhat redundant with the schema.

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 two-param read tool with no output schema and no param docs, the description should at least sketch the block/tag argument and the returned block. It covers purpose, cost, and idempotency adequately but leaves the parameter semantics and return shape 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 50%: idempotencyKey is documented in the schema, but the two-element params array (block number/tag and full-transaction boolean) is undocumented anywhere. The description adds no meaning to those parameters, so it fails to compensate for the gap.

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 (Read) and resource (eth_getBlockByNumber) plus the chain (eip155:1), so an agent knows it fetches a block by its number/tag. The method name itself implicitly distinguishes it from the by-hash sibling, though the description never spells that out.

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?

Only 'Preserve the private idempotencyKey for retries' gives any usage direction, and that is about retries rather than tool selection. There is no guidance on when to use this versus eth_getBlockByHash or the other block-number siblings.

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