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

Annotations mark readOnlyHint=false and openWorldHint=true, and the description explains the non-read-only flag ('each call is charged') while adding pricing, free failures, and 404-uncharged behavior. This goes well beyond the annotations and does not contradict them.

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 purpose and outputs are front-loaded, then usage, error semantics, example, pricing, and the read-only rationale follow in compact sentences. The length is justified by the paid-call and annotation-explanation needs.

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 lists the returned fields (hash, timestamp, tx count, gas, base fee, producer) and covers default, error, charging, and free-call behavior. This is complete for calling the tool correctly.

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 number/latest. The description adds format detail ('decimal number') and an example, but not enough to require a full 5.

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 gives a specific verb ('Fetch') and resource ('a block on Polygon PoS'), including the default 'latest' and the returned fields. It also names polygon_gas as the alternative for current fees, so it is distinguishable from 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?

It explicitly states the use cases ('timestamps and confirmation counts') and redirects fee lookups to polygon_gas. The omission/default behavior for number and the 404 case are also described, leaving little inference.

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