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

Annotations cover safety (readOnly, non-destructive) but the description adds the pricing model ($0.01/call, first 25 free, failures free), the error contract (404 for missing contract, 422 for non-ERC-20, both uncharged), and explains why idempotentHint=false matters: 'each call is charged, so repeats are not free.' That is real value beyond the annotations.

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?

One dense paragraph, front-loaded with what/why, then input resolution, then pricing. Every sentence carries information, though the pricing sentence is long and could be split for scanability.

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?

No output schema exists, and the description compensates by naming the return fields (raw allowance, token-denominated allowance, unlimited flag). Combined with the error and pricing contract, an agent has everything needed to call this correctly and interpret results.

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 baseline is 3. The description still adds resolution semantics the schema lacks: token accepts a ticker or a 0x contract, with 404/422 behavior on bad input. It doesn't extend owner/spender meaning, but those are already well documented.

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+resource+chain - ERC-20 allowance on Arbitrum One - and spells out the three returned facts (raw allowance, token units, unlimited flag). Explicitly distinguishes itself from arb_token_balance, which the sibling list confirms exists.

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 both positive triggers ('check an approval before a swap', 'audit risky open approvals') and an explicit alternative with its condition ('for the owner's balance use arb_token_balance'). An agent can route without opening either schema.

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