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

With annotations supplied, the description still adds real behavior: the call costs $0.001 in USDC on Base per successful call via x402, and the returned count includes pending transactions — both material facts not derivable from readOnlyHint/openWorldHint/idempotentHint. It doesn't describe failure/billing-on-error behavior or auth flow beyond naming x402, keeping it out of 5 territory.

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 short sentences: what it is, when to use it, what it costs. Scope is front-loaded before usage and pricing, and no sentence is 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?

For a one-parameter read tool with no output schema, the description covers purpose, usage, and payment. The only ambiguity is the return shape — 'both confirmed and including pending' could mean two values or one combined count — which a missing output schema leaves unresolved.

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?

One parameter with 100% schema description coverage ('0x address'), so the schema already carries the parameter contract. The description only references 'an address' generically and adds no format, chain-scoping, or validation detail beyond it — the prescribed baseline of 3.

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 chain: 'Transaction count (nonce) of an address on Polygon PoS,' and qualifies the scope as 'both confirmed and including pending transactions.' It does not explicitly distinguish itself from siblings such as polygon_tx or polygon_balance (or from the parallel eth_nonce/base_nonce/op_nonce variants), so it stops short of a 5.

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 two concrete use cases: 'Use to build the next transaction or to tell whether an address has ever sent anything.' That is clear when-to-use context, but there is no when-not guidance and no named alternative (e.g. when to prefer polygon_tx for history).

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