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

Beyond the annotations (readOnly/openWorld/non-destructive/non-idempotent), the description adds material operational facts: malformed address or slot returns 400 and is uncharged, failed calls are free, and each successful call is charged so repeats are not free. It also discloses the dual return representation. This is real context rather than restatement.

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?

Front-loaded with the core action and return shape, then usage, errors, pricing in a sensible order. Slightly redundant at the tail: 'each call is charged, so repeats are not free' restates the earlier 'Price $0.01/call' clause and could be trimmed.

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?

No output schema exists, and the description compensates by describing the returned 32-byte word in both numeric and address form. Combined with error behavior and cost model, 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%, so the baseline is 3; the description earns an increment by explaining that a slot may be a decimal index or a 0x 32-byte key and that keyed form is used for mapping and proxy slots — meaning the schema does not convey. It also supplies a concrete address example.

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 and resource: 'Read one raw storage slot of a contract on Arbitrum One (eth_getStorageAt)'. It also pins the return shape (32-byte word as number, and as address when applicable), which lets an agent distinguish it from arb_call, arb_balance, and the other arb_* readers without opening the schema.

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 names the use case ('contract state that has no getter, owners or implementation pointers') and routes the proxy case to the sibling: 'for proxies use arb_proxy'. Both when-to-use and when-to-use-something-else are present.

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