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

Annotations already cover read-only and non-destructive, but the description adds information annotations cannot convey: pricing ($0.002/call via x402 USDC or card key, first 25 free, failed calls free) and the explicit warning that repeat calls are charged, which materially explains the idempotentHint=false billing behavior. It also reaffirms 'reads or computes only and changes nothing' and enumerates the return payload.

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-loads what is checked and why, then behavior and pricing; three sentences with no filler. The pricing/free-tier clause is dense but justified for a paid tool, though it slightly crowds the middle of an otherwise tight definition.

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 compensates by listing the exact return fields, and it covers cost, safety profile, and intended workflow for a simple 3-parameter read tool. An agent has everything needed to decide to call it 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 description coverage is 100% and all three parameters (owner, token, spender) are documented in the schema with role and address format. The description restates the owner/spender relationship but adds no format, constraint, or edge-case detail beyond the schema, so the baseline 3 applies.

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 precise verb and resource ('check how much of a wallet's ERC-20 token a spender contract is approved to move on Base') and even enumerates what comes back (raw/formatted allowance, symbol, decimals, unlimited flag). The 'approved to move' phrasing cleanly separates it from the sibling balance tools (base_token_balance) and the chain prefix separates it from eth_allowance/arb_allowance etc.

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 two concrete usage contexts: pre-swap/pre-deposit approve checks and auditing risky unlimited approvals. It does not name an alternative tool or state when-not to use it, so it stops short of the explicit routing a 5 requires.

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