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

With no annotations, the description carries the full burden and does well: it reveals the underlying eth_getBlockByNumber call, the semantic meaning of the output (head staleness), and the cost/payment model ($0.005 per call over x402/USDC). It omits rate limits and error behavior, but the cost and method disclosure is unusually valuable.

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?

Front-loaded with what the tool returns, then use case, then method and price. Four short clauses, each earning its place with zero filler.

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?

No output schema exists, so the description properly explains return values (chain id, block height, staleness). For a zero-required-parameter health check, nothing an agent needs to invoke it correctly is missing.

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?

Only one optional parameter and schema coverage is 100%, so the schema already documents the chain filter and its valid values. The phrase 'every supported chain in one call' weakly mirrors the omit-to-get-all behavior but adds no syntax or meaning beyond the schema, so baseline 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?

States a specific resource and scope ('Live health of every supported chain in one call') and enumerates the returned fields (chain id, block height, staleness). It is clearly distinguishable from single-chain siblings like evm_block or evm_fees because it aggregates health across all chains.

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?

Provides a clear use case: 'Use it to pick a chain that is actually responding.' That is actionable context, but it names no alternative tool and states no when-not-to-use conditions, so it falls short of explicit routing guidance.

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