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

With no annotations supplied, the description usefully discloses the exact charge, accepted payment networks, lack of account or API-key requirements, and that failed calls are not charged. It also identifies DefiLlama as the data source, but does not explicitly state read-only behavior or provide freshness and response-format details beyond 'live'.

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 dense and front-loaded, identifying the paid nature and data scope immediately. Each subsequent statement adds distinct invocation-relevant information about cost, authentication, failure charging, or the endpoint, with no 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?

For a zero-parameter endpoint, it covers the asset, available metrics, source, price, payment networks, authentication requirements, failure behavior, and URL. Because there is no output schema, the lack of exact response structure, field units, and payment-execution details prevents full completeness.

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?

The tool has zero parameters, so the baseline score of 4 applies. The fixed M-specific URL reinforces that the asset is predetermined and no symbol, date range, or chain-selection inputs are needed.

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 identifies the exact resource, 'M by M0 (M)', and enumerates live metrics: price versus peg, supply, supply changes, and per-chain supply. This clearly establishes a data-retrieval purpose despite the potentially misleading 'buy_' prefix, though it does not explicitly differentiate itself from sibling stablecoin or general crypto-price tools.

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 live M-stablecoin metric list provides an implied use case, while the payment and authentication details help assess whether calling it is practical. However, there is no explicit guidance on when to prefer it over buy_crypto_price or another buy_stable_* tool, and no when-not conditions.

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