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

Beyond the readOnly/destructive/idempotent annotations, the description adds concrete behavioral facts: an unknown hash returns 404 and is not charged, failed calls are free, the first 25 calls are free, and pricing is $0.01/call via x402 USDC or a card key. The note that each call is charged, so repeats are not free, corroborates idempotentHint=false.

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?

It is front-loaded with purpose and the sibling routing, and the example hash is useful. Some sentences restate annotations ('reads or computes only and changes nothing') and the pricing paragraph is dense, but the information is not padding.

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?

For a single-parameter lookup with no output schema, the description covers return fields, error behavior, cost, and alternatives. Nothing an agent needs to call it correctly is missing.

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%, so the hash format is already documented; the description reinforces it and adds a real example hash plus the 404 semantics for an unknown hash, which is meaningful beyond the schema. It stops short of describing any normalization of case or malformed-hash behavior.

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 and resource ('Look up a zkSync Era transaction by hash') and enumerates the returned fields: sender, recipient, value, nonce, gas limit, function selector and block. It also explicitly distinguishes itself from sibling tools zksync_receipt (status and fees) and zksync_logs (events).

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 explicit when-to-use guidance ('see what was sent or whether it exists') and names the alternatives for adjacent tasks: zksync_receipt for success/failure and fees, zksync_logs for emitted events. There are no significant gaps.

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