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

Beyond the annotations, the description discloses the pricing mechanism ($0.001 USDC on Base, x402) and, crucially, that billing is per successful call — cost/authorization behavior an agent cannot see in the schema. It also clarifies that the returned figure combines confirmed and pending counts, which matters semantically. Note that annotations mark readOnlyHint=false even though this is a pure query, a mild tension the description neither confirms nor resolves.

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?

Two sentences, zero filler, and the core definition is front-loaded ahead of the usage hint and pricing note. Every clause earns its place.

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, no-output-schema tool, the definition covers what it returns conceptually (confirmed + pending counts), when to use it, and the cost of calling it. The only gap is the return shape — it implies two values but doesn't say how they are structured, which an agent must discover at call time.

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?

There is a single parameter with 100% schema description coverage ("0x address"), so the schema already carries the parameter documentation. The description adds only that the address is on Arbitrum One; it gives no format details beyond the schema. 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 precise verb+resource: the transaction count (nonce) of an address, explicitly scoped to Arbitrum One and covering both confirmed and pending counts. That scope cleanly separates it from arb_balance, arb_tx, and the same tool on other chains (eth_nonce, base_nonce, op_nonce, polygon_nonce) without opening another 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?

"Use to build the next transaction or to tell whether an address has ever sent anything" gives two concrete use cases, which is real when-to-use guidance. It stops short of naming an alternative or an exclusion (e.g. use arb_tx for history), so it lands at 4 rather than 5.

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