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

Annotations already declare readOnly, idempotent, non-destructive, and open-world, so the safety profile is covered. The description adds genuinely non-obvious behavior: a 10 calls/day free tier, then $0.001/call, with payment via x402 in params._meta or HTTP, or via X-API-Key credits. That payment/auth detail is exactly the kind of context annotations cannot convey, though it stops short of saying what happens when payment is missing.

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 returned-fields list, with pricing and transport details bracketed at the end. The single dense sentence is efficient, though the eight-item field list reads as a run-on and could be structured as a short list for faster scanning.

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?

An output schema exists, so return-value explanation is unnecessary, and annotations cover the safety profile. Given a simple three-parameter read tool, the description covers the remaining gaps — what it returns, the optional holder mode, and the paid-access mechanics — leaving only sibling routing unaddressed.

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% and each of the three parameters carries a description and example, so the baseline is 3. The description adds one useful clarification — that holder is optional and triggers a balance read — but nothing about chain naming conventions or address format beyond what the schema supplies.

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 names the exact resource (any ERC-20 token) and enumerates the specific facts returned: name, symbol, decimals, total supply, owner, paused status, proxy detection, and an optional holder balance. It is clearly distinguishable from generic chain tools, though it never explicitly contrasts itself with the sibling token_balances, whose territory the optional holder-balance feature partly overlaps.

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?

There is no when-to-use or when-not-to-use guidance. The agent must infer that this is the metadata-lookup tool and that token_balances is for multi-holder balance queries; the description gives no such routing signal or prerequisites.

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