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

Annotations provide only readOnlyHint: true. The description adds valuable behavioral context beyond that: limitations ('One block per call', 'Ethereum mainnet and Base only') and the caveat that historical base fee data depends on RPC node retention. It does not contradict the read-only annotation and covers the key operational constraints.

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 well-organized into purpose, usage, limitations, and alternatives. It is front-loaded with the core function and each section earns its place. However, at seven sentences it is slightly longer than strictly necessary; still, no filler or redundancy.

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?

With an output schema present, return values are already defined. The description covers what the tool does, when to use it, alternatives, and limitations. For a simple read-only block-fetch tool, this is complete enough for an agent to call it correctly without additional information.

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 100%, so the input schema already explains both parameters (chain_id, block_identifier). The description mentions 'by number, hash, or latest' and 'Ethereum and Base', but these are also present in the schema. It adds no new parameter-level meaning, so the baseline of 3 applies.

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 states a specific verb and resource: 'Get block details' and lists the exact fields (timestamp, gas used, base fee, miner, transaction count) and acceptable identifiers (number, hash, 'latest'). It also frames the purpose with 'Use to anchor events to a point in chain time', distinguishing it from related tools like get_transaction and get_gas_price.

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 includes an explicit 'Use when' section with concrete examples (dating a transaction, checking congestion) and a direct exclusion: 'For current fee levels use get_gas_price instead.' It also lists alternatives (get_transaction, get_gas_price), giving the agent clear direction on when to choose this tool over siblings.

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