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

Annotations already declare readOnlyHint=true and destructiveHint=false, yet the description adds genuinely new behavior: no state changes, per-call charging ($0.01 via x402/card key, first 25 free, failed calls free), and why repeats aren't free — which explains the otherwise puzzling idempotentHint=false. It stops short of describing the exact output object, but with no output schema and a simple payload that is a minor gap.

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?

Purpose, verdicts, scope, usage, alternative, example, and pricing are front-loaded in a single dense paragraph with little waste. There is slight redundancy at the end — "each call is charged, so repeats are not free" restates the pricing clause — which keeps it off a 5.

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 one-parameter, read-only, no-output-schema tool, everything an agent needs is present: input format with example, the meaning of each possible result, chain scope, the sibling to use for a different question, and the cost model. Nothing material 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?

Schema coverage is 100% and the parameter already documents "0x address (40 hex characters)", so the baseline is 3. The description adds value by supplying a concrete worked example address and making clear that all-lowercase, all-uppercase, and mixed-case inputs are all accepted, which the schema does not say.

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: validates an EVM address and returns its EIP-55 checksummed form, and enumerates the four possible input-case verdicts. It also names the sibling tool (evm_is_contract) it must not be confused with, so an agent can distinguish it from the ~200 chain-prefixed siblings.

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?

Explicit when-to-use ("Use before sending funds or storing an address") and an explicit alternative with the condition that selects it ("for whether it is a contract use <chain>_is_contract"). Scope is also stated (works for every EVM chain), removing ambiguity with the per-chain siblings.

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