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

Beyond the annotations (readOnly, openWorld, idempotent=false, destructive=false), it discloses error semantics (404 for missing contract, 422 for non-ERC-20, both uncharged), pricing ($0.01/call via x402 or card key, first 25 free, failed calls free), and explains why repeats are not free due to per-call charging. It also explicitly states it reads/computes only and changes nothing, consistent with readOnlyHint.

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-loaded with the core definition, then usage, alternative, token resolution, errors, and pricing — a logical order. It is a single dense paragraph with minor redundancy (restating read-only behavior alongside cost-per-call), but every sentence carries operational information for a paid tool.

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 does the work of describing the return (raw allowance, token-unit allowance, unlimited flag) and the failure modes, which is sufficient to call it correctly. It does not name return field names, leaving a small gap for downstream parsing.

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, and the description adds resolution semantics beyond the schema: token may be a ticker or a 0x contract, with a missing contract yielding 404 and a non-ERC-20 yielding 422. It does not add further detail on owner/spender beyond the schema descriptions, so it stops short of 5.

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 (ERC-20 token allowance on Unichain) and defines the returned concept precisely: how much a spender may move from an owner, raw and in token units, plus whether the approval is unlimited. It explicitly contrasts with unichain_token_balance, so an agent can distinguish it from the closest sibling without opening the schema.

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 when-to-use cases ('check an approval before a swap', 'audit risky open approvals') and names the correct alternative for the adjacent question ('for the owner's balance use unichain_token_balance'). Nothing about tool selection is left to inference.

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