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 new operational context: the x402 payment model and its cost ($0.002 USDC on Base), plus the fact that the result includes an unlimited-approval flag. It stops short of describing failure modes or latency.

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?

Three short sentences: purpose first, then usage timing, then inputs and price. Every sentence carries distinct information and nothing is repeated from the schema.

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 simple read-only tool with no output schema, the description covers purpose, call timing, inputs, and cost. It partially characterizes the return ('how much', 'whether unlimited') but does not specify the exact response shape or units, which is the only notable gap.

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 schema contributes only names and address patterns. The opening sentence defines the roles indirectly (owner holds the balance, spender is approved by owner, token is the ERC-20), which is real added meaning, but the input list itself ('Input: token, owner, spender') adds nothing and no parameter is explained individually.

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?

Names a specific verb and resource ('ERC-20 allowance check on Base') and states exactly what the result answers: how much a spender may still move from an owner's balance and whether the approval is unlimited. This cleanly separates it from siblings like base_erc20_balance or base_token, which read different state.

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?

Gives explicit timing guidance: 'Run before a swap, an approve or a revoke.' That is clear context for when the tool is appropriate. It does not name an alternative tool or state when this is the wrong choice, so it falls short of a 5.

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