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

Annotations cover readOnly/openWorld/non-idempotent, but the description adds genuinely new behavior: billing is per call ($0.002 via x402 USDC or card key), the first 25 calls are free, failed calls are free, and repeats are not free because each call is charged. This is the key operational trait for a non-idempotent paid call; it stops just short of describing return shape beyond field names.

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?

Dense but front-loaded: scope and return fields first, then routing to polygon_gas, then error and pricing. The pricing sentence carries some provider-specific detail (x402, /credits) but it earns its place for a metered tool; nothing is padded.

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?

With no output schema, the description enumerates the returned fields (hash, timestamp, tx count, gas used and limit, base fee in gwei, producer), states the error behavior, and discloses billing. An agent has everything needed to call it correctly and interpret the result.

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 schema already documents the 'latest' default, so the baseline is 3. The description adds that an explicit value is a decimal block number and gives a concrete example (number=latest), which is marginal but useful syntax guidance.

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+resource+chain: latest block number and details on Polygon PoS, or any block by number, and enumerates the returned fields. It is immediately distinguishable from polygon_gas and other polygon_* 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?

Explicitly says what to use it for (timestamps, confirmation counts) and names the alternative for the other case ('for current fees use polygon_gas'). It also covers the failure case: a block that doesn't exist yet returns 404 and is uncharged.

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