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

With annotations already marking this as read-only and open-world, the description adds valuable behavioral context: the $0.002 USDC cost per successful call, x402 payment options across Base, Solana or Arc, and the fact that failed calls are not charged. It does not discuss rate limits or response shape, but the output schema likely covers the latter.

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?

The description is three tightly packed sentences: it front-loads the data returned, then explains checkpoint meaning and exclusions, then covers pricing. No sentence is wasted, and the payment detail is useful for invocation.

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?

Given the output schema exists and annotations cover read-only/open-world behavior, the description supplies everything else an agent needs: scope, count range, excluded data, returned fields, and cost/payment behavior. Nothing critical is missing for correct invocation.

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 description coverage is 100%, and the single `count` parameter is already fully documented in the schema as '1 to 10 (default 3)'. The description repeats the range but adds no new parameter semantics beyond what the schema provides, so the baseline of 3 is appropriate.

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?

The description states a specific verb/resource combination: 'Polygon PoS checkpoints from the Heimdall API'. It also enumerates the returned fields (Bor block range, timestamp, proposer, average spacing) and explicitly excludes state-sync logs, which lets an agent distinguish this from adjacent chain-data tools.

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?

It gives clear usage context by specifying the latest K checkpoints (1 to 10) and explicitly excluding state-sync logs. It does not name a specific alternative sibling tool or spell out when-not-to-use conditions beyond that exclusion, so it falls short of the top score.

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