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

Annotations already declare readOnlyHint/destructiveHint=false, but the description adds real value beyond them: malformed input returns 400 uncharged, failed calls are free, and it explains the idempotentHint=false by noting each successful call is charged so repeats are not free. Pricing and auth (x402 USDC or card key /credits, first 25 free) are also disclosed. The only gap is that it doesn't describe error behavior beyond 400 or rate limits.

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?

Purpose and return shape are front-loaded, then usage, then errors and pricing – a sensible order. It is dense with useful facts, though the pricing sentence is long and partially repeats the charge/free idea already implied earlier.

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 carries the return-value burden itself ('the 32-byte word, as a number and, when it holds one, as an address'), and it also covers error handling, cost, and the proxy alternative. 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 baseline is 3, but the description goes beyond the schema by explaining why a 0x 32-byte key matters ('mapping and proxy slots') and gives a concrete example address. It doesn't add format detail for the decimal slot beyond what the schema states.

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 Base (eth_getStorageAt)') and immediately pins down the scope of the returned word. It also names the sibling it is not (base_proxy), so an agent can distinguish it from base_call/base_proxy without opening schemas.

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?

'Use to inspect contract state that has no getter, owners or implementation pointers' gives concrete when-to-use conditions, and 'for proxies use base_proxy' names the alternative that supersedes it. Both the positive case and the exclusion are explicit.

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