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

Annotations already declare readOnlyHint=true and openWorldHint=true, so the safety profile is covered. The description adds genuinely useful context beyond that: the paid cost ($0.002 USDC on Base via x402) and the semantics of the returned allowance. It does not mention rate limits, caching, or failure modes, keeping it at a 3.

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?

Two compact sentences: the purpose first, then the usage cue in parentheses, then the price. Nothing is wasted, though bundling the cost note into its own sentence adds little to call-time decisions.

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 read-only three-parameter allowance lookup with no output schema, the description covers purpose, usage context, and pricing. It falls short on explaining the return value's formatting (raw wei vs. decimal) and on documenting the individual address parameters, which is a real gap at 0% schema coverage.

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 description coverage is 0%, so the description must carry parameter meaning. It partially compensates by describing the relational roles (spender moving from an owner's ERC-20 balance) and the token reference, but gives no per-parameter explanation, format, or constraints beyond the visible address regex.

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 (ERC-20 allowance) and states exactly what the return value represents: how much a spender may move from an owner's balance. It is clearly distinguishable from balance siblings like base_erc20_balance, though it does not explicitly name them.

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?

The parenthetical '(approval check before swaps or revokes)' gives concrete when-to-use context, which is more than most tool definitions offer. It stops short of naming an alternative tool or stating exclusions, so it does not reach a 5.

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