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

Annotations already include readOnlyHint, idempotentHint, and destructiveHint=false. The description adds important behavioral context beyond annotations: it is read-only (confirming the annotation), costs 10 weighted units (metered on the user's key), requires an API key, and notes that token availability depends on 'data-capable upstream' existence. This is rich, supplementary behavioral disclosure.

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 information-dense but well-structured: first sentence defines the operation and scope, second gives use cases, third names exclusions and alternatives, fourth summarizes the return JSON, and fifth covers read-only/cost/auth. Every sentence earns its place, with critical details front-loaded. No fluff or redundancy.

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?

Given the tool's simplicity (2 required params, no output schema) and strong annotations, the description covers all needed aspects: what it does, when to use it, what it returns (JSON structure), its safety profile (read-only, idempotent), cost, and authentication requirements. An agent can invoke it correctly without additional information.

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 both 'chain' and 'address' are well-documented in the schema. The description adds value by enumerating the allowed chain slugs and clarifying that the address format differs per chain (0x… for EVM, base58 for Solana), which slightly exceeds the schema's brief examples. This is a meaningful enhancement over the schema alone.

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?

The description clearly states the tool retrieves native and ERC-20 balances for an address on a specific chain, listing supported chains. It explicitly differentiates from get_history and rpc_call, making its purpose unambiguous relative to siblings.

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?

The description gives concrete use cases ('portfolio or pre-flight funds check') and explicitly states what it is NOT for, naming the alternative tools (get_history for transfer history, rpc_call for raw eth_getBalance). This provides clear guidance on when to use this tool versus alternatives.

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