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

Annotations already declare readOnly, idempotent, and non-destructive behavior. The description adds valuable context beyond those: the cost ($0.001 per call), the formatting behavior (human-readable), and the supported chains. It does not contradict annotations and enhances the agent's understanding of side effects (none) and operational constraints.

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 mostly concise and front-loaded: it states the purpose first, then cost, chains, and an example. The example URL is somewhat long and could be trimmed, but it serves as a concrete reference. Overall, it is efficient and structured without redundant filler.

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 output schema exists, the description does not need to detail return values. It covers cost, supported chains, and formatting behavior, which are essential for an agent to invoke correctly. It omits nothing critical for a simple balance lookup, though it doesn't mention edge cases like invalid addresses or unsupported tokens, which are likely handled by error responses.

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% for all three parameters (chain, token, owner), each with a clear description. The description does not add extra parameter-level semantics beyond what the schema provides; the example URL with concrete addresses is illustrative but not explanatory. Thus, 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?

The description clearly states the tool returns a formatted, human-readable ERC-20 token balance, explicitly contrasting it with a raw integer that needs conversion. It names the exact operation (balanceOf plus decimals) and the resource (token), and the phrasing 'not a raw 18-digit integer' effectively distinguishes it from raw balance endpoints. Though it doesn't name a specific sibling, the purpose is unambiguous and specific.

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 provides practical context: cost per call and supported chains, which help an agent decide feasibility. However, it does not explicitly state when to use this tool over alternatives (e.g., chain_balance for native tokens or chain_token_balances for multiple tokens). The usage context is implied by the title and description but lacks explicit exclusions or alternative routing.

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