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

Annotations already cover read-only and non-idempotent, but the description adds real context beyond them: that the count includes pending transactions, that malformed addresses return 400 without charge, that each call is billed $0.01 (first 25 free, failures free), and that repeats are not free. It effectively explains the non-idempotent annotation, which 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?

Purpose and the balance alternative are front-loaded, and every sentence carries information. The pricing and free-call detail is useful but makes the description longer than strictly necessary for a one-parameter read tool.

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 single-parameter read tool with no output schema, error behavior, pricing, and pending-vs-confirmed semantics are covered. The only soft spot is that it doesn't clarify the shape of the result (e.g., whether confirmed and pending counts are returned as separate fields).

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%, so the baseline is 3; the description still earns credit by adding a concrete example address and stating that malformed addresses are rejected with 400, which tells the agent the input is validated rather than silently coerced.

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: read the transaction count (nonce) of a 0x address on Polygon PoS. It also distinguishes itself from the sibling polygon_balance explicitly, so an agent can route between them without inspecting schemas.

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?

Gives concrete use cases (building the next transaction, checking whether an address has ever sent anything) and names the alternative tool (polygon_balance) for the adjacent need. That is explicit when-to-use plus a named alternative, which is the top of the scale.

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