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

With no annotations, the description carries the burden and does well: it discloses auth requirements (no API key, no account), cost and payment rail ($0.005 per call over x402/USDC), and the exact per-chain return fields including staleness. It stops short of saying what a chain that is down looks like in the response (omitted vs. ok=false) or any rate/failure behavior, which keeps it below a 5.

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 sentences, each doing distinct work: selection criteria, exclusions, and cost/auth. The decision-relevant guidance is front-loaded and nothing is redundant.

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 enumerates the return fields itself, and it covers the payment model an agent must know before calling. For a zero-required-param read tool this leaves nothing material unsaid.

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% and the single parameter already documents the enum values and the 'all when omitted' default. The description's 'every supported chain in a single call' corroborates but adds no syntax or format detail 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 verb and resource — enumerate every supported chain with chain id, block height, head staleness in seconds, and ok — in one call. It explicitly distinguishes itself from evm_block, evm_gas, and evm_fees, so an agent can route without opening a schema.

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?

Front-loads the use case ('when an agent has to pick a chain that is actually answering before it commits to one') and gives explicit exclusions naming the sibling endpoints for single-chain lookup and gas/fee pricing. Both when-to-use and when-not-to-use are stated.

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