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

Annotations cover the safety profile (readOnly, idempotent, non-destructive, openWorld), yet the description adds material context beyond them: the data source (UserOperationEvents across both EntryPoints), the exact kost/access model ($0.05/call over x402 on Base, prepaid x-credit-token for unlimited, no free tier, no API key), and an interpretive caveat that fully-sponsored accounts are typically app/agent-operated plus 'not financial advice'.

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 the question and the mechanism, then the enumerated outputs, then parameters and pricing, so a skimmer gets the point immediately. It is slightly over-long with some restatement ('wallet= required' vs 'Required input: wallet') and pricing detail that could be tighter.

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 two-parameter read tool with an output schema, the description covers inputs, data sources, cost/auth requirements, and interpretation limits, which is more than sufficient. Return-value explanation is partly redundant given the output schema exists, but nothing essential 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 adds semantics the schema lacks: 'days' defaults to 30 and is capped at 90, and 'wallet' is reiterated as required. Those constraints are not present in the schema descriptions.

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 precise verb+resource ('who pays this wallet's gas') and defines the exact mechanism (paymaster sponsorship of a smart account, read from UserOperationEvents across EntryPoints v0.6/v0.7). It is clearly distinguishable from blanket wallet-introspection siblings and from the adjacent paymaster_check tool because it frames the answer around sponsorship attribution.

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 strong context for when the tool matters ('invisible to every does-this-wallet-spend-ETH heuristic'), telling the agent this is for sponsorship/smart-account detection rather than generic balance checks. It never explicitly names a sibling tool to use instead, so it stops short of full when/when-not routing.

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