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

With no annotations, the description carries the full burden and does well: it explicitly discloses retry-with-backoff and last-known-good cache fallback, so an agent understands the tool degrades gracefully rather than failing. It omits rate limits, auth requirements, and staleness bounds on the cached value, which keeps it short of a 5.

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?

Two tight sentences, purpose front-loaded, no filler. The second sentence is partly promotional (paid endpoint) but still conveys a real deployment trade-off.

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?

No output schema and no annotations exist, yet the description states what is returned (ETH/USD price), how failures are handled, and the cost model. It lacks only the precise return shape (e.g., quote currency, decimals, timestamp), which a caller would want given there is no output schema.

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?

There is only one optional parameter and schema description coverage is 100%, so the schema already fully documents simulateFailureRate. The description adds no additional parameter meaning, which is the expected baseline when the schema does the work.

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 states a specific verb+resource ('ETH/USD price') and even discloses the retrieval mechanism (retry-with-backoff plus last-known-good cache fallback), which is more than a bare restatement. It does not differentiate against siblings like get_freshness_priced_data or get_market_snapshot, which could plausibly return overlapping price data.

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 implies usage by noting the MCP route is free and a pay-per-call URL exists 'for production/agentic use', which is a soft cue about context. However, it never says when to prefer this tool over the sibling price/market tools, nor any prerequisites or exclusions.

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