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

Annotations already declare readOnly, idempotent, openWorld, non-destructive, so the safety bar is low. The description adds genuinely non-obvious context: the DefiLlama data source, the 2% depeg threshold, and the access model (x402 at $0.01/call, prepaid x-credit-token header, 1 free call/day, no API key) – details an agent cannot infer from annotations.

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?

Purpose and the sibling alternative are front-loaded, but the tail is padded with boilerplate ('Not financial advice', a full pricing/payment paragraph) that is more marketing than operational guidance and lengthens the definition without adding selection value.

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 values need not be explained, and the single parameter is fully documented. Combined with annotations and the data-source and pricing notes, the definition is complete enough to call correctly, with only minor redundancy.

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 there is only one optional parameter, whose default and max are fully documented in the schema. The description adds nothing about limit semantics, so the baseline of 3 is correct.

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 a specific resource and scope: total stablecoin market cap, largest coins by circulating supply across all chains, peg type/mechanism, live price, and a depeg watch for USD-pegged coins 2%+ off peg. It explicitly distinguishes itself from the sibling stablecoin-peg, so an agent can route without opening a 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?

It gives a clear use case (the stablecoin-market commodity agents track) and an explicit alternative with its own condition: 'for a single Base-stablecoin peg check use stablecoin-peg'. There is no broader when-not guidance against other market tools such as crypto_markets or crypto_global, so it stops short of a 5.

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