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

Annotations already declare readOnlyHint=true and destructiveHint=false, and the description reinforces this ('reads or computes only and changes nothing') while adding non-annotation context: pending vs confirmed inclusion, malformed address → 400 with no charge, and cost/pricing with first 25 free and failed calls free. The one gap is that it never names the returned fields, which matters for a tool with no output schema.

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?

Front-loaded with the verb and resource, then usage, then safety/cost — a sane information hierarchy. It is dense but slightly overstuffed, and 'failed calls free' and 'each call is charged, so repeats are not free' partially restate the same billing point.

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?

Covers purpose, redirection, validation behavior, billing, and the destroyed/non-destroyed nature of the call — enough to invoke correctly. With no output schema, however, it leaves the return shape underspecified: 'both confirmed and including pending' implies either two fields or one, and the agent cannot tell which.

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% for the single 'address' parameter, so the baseline is 3. The description adds only an example value and the validation consequence (400 on malformed input), which is useful but does not deepen semantics beyond the schema's '0x address'.

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') and immediately disambiguates the obvious sibling by redirecting balance lookups to polygon_balance. The chain is stated explicitly, so it is distinguishable from eth_nonce/arb_nonce/base_nonce 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?

Gives two concrete use cases ('build the next transaction', 'tell whether an address has ever sent anything') and names the alternative for the adjacent case ('for its balance use polygon_balance'). The condition selecting the sibling is explicit rather than inferred.

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