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

Annotations already declare readOnlyHint and openWorldHint, so the safety profile is covered. The description adds real behavioral information beyond that: the data source (public block explorer API), the cost model ($0.002 USDC per successful call via x402 on Base, Solana or Arc) and explicitly that failed calls are not charged. It does not discuss pagination limits or rate limiting, but for a read-only paid endpoint this is solid disclosure.

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 sentences, front-loaded with the resource and scope, followed by the exclusion and then the pricing caveat, which is the right order for an agent deciding whether to call. Minor waste in re-listing output fields (batch number, time, status, tx counts, chain ids) that an output schema already covers. No filler or marketing language.

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 a single optional parameter, an output schema and read-only annotations, the description supplies everything needed: what the rows are, the allowed range, the hyperchain exclusion, and the payment model including no-charge on failure. Remaining gaps are minor — no guidance on what an empty result means (no recent batches) or whether the newest batch may be in a partial state.

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 single parameter is fully documented (count of newest batches, 1 to 20, default 5). The description restates the same 1-to-20 range and 'newest N' semantics without adding ordering rules, error behavior for out-of-range values, or anything else beyond the schema. Baseline 3 is appropriate when the schema carries the parameter semantics.

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 names the specific resource (zkSync Era rollup batches from the public block explorer API) and the exact scope (the newest N batches) and enumerates the fields returned, so an agent can tell it returns batch-level data rather than transactions or proofs. It also scopes out hyperchain data, which separates it from generic L2 tools like crypto_arbiscan_l2_rollup or crypto_scroll_l2_zk_proofs. It stops short of a crisp verb+resource opening sentence and never names a sibling tool explicitly.

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?

Usage is implied rather than stated: the agent infers 'use this when you need recent zkSync Era batch state'. The one explicit exclusion ('Hyperchain (other zkSync chains) data is not included') is genuine when-not guidance, but no alternative tool is named for hyperchain data and no prerequisites are given. Pricing context helps decide whether to call but is not usage guidance.

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