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

Annotations already provide readOnlyHint, destructiveHint, openWorldHint, and idempotentHint. The description adds valuable context beyond that: pricing model ($0.01/call, first 25 free, failed calls free), error responses (404 for missing contract, 422 for non-ERC-20, both uncharged), and a clear statement that the tool reads/computes only and changes nothing.

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?

The description is front-loaded with purpose and efficiently covers usage, parameter details, pricing, and safety. It is slightly dense with pricing/error details, but every sentence serves a purpose.

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, but the description explains the return values (raw and token units, unlimited flag). Combined with annotations and full schema coverage, an agent has all needed information to call the tool correctly.

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%, so the schema already documents all three parameters. The description repeats the token format (ticker or 0x contract) and adds error codes, but does not add meaning for owner or spender beyond the schema. Baseline 3 is appropriate.

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 and resource: 'ERC-20 token allowance on HyperEVM' with details on what is returned (raw and token units, unlimited flag). It also differentiates from the sibling balance tool by name.

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?

Explicitly gives use cases ('check an approval before a swap or to audit risky open approvals') and names the alternative tool for a different need ('for the owner's balance use hyperevm_token_balance'). Clear when-to-use and alternative routing.

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