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

Annotations already declare readOnlyHint, openWorldHint, idempotentHint, and destructiveHint=false, covering the safety profile. The description adds valuable behavioral context beyond annotations: it specifies the data scope (up to 365 days of history), the averages calculated (7d/30d), the extremity classification, and that the service is free. This goes beyond what annotations provide and helps the agent understand the returned data.

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 three short, information-dense sentences with no redundancy. It front-loads the core function (index value and history), then adds source, frequency, and cost. Each sentence contributes new, non-overlapping information, and there is 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 simple tool with one optional parameter and no output schema, the description adequately explains what the agent will receive: current index, historical values, 7/30-day averages, and extremity classification. It also notes the data source and update frequency. While it does not specify the exact response format (e.g., JSON structure), it covers the essential content an agent needs to decide and call the tool correctly.

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 schema has zero description coverage for the single 'days' parameter, so the description must compensate. It mentions 'Up to 365 days of history', which implies the 'days' parameter controls the history length, but it does not explicitly state that 'days' is the number of days to include. This provides a helpful hint but leaves the mapping implicit, so it's not fully explicit.

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 explicitly names the resource (Crypto Fear & Greed Index), the value range (0–100), and the specific outputs (current value, history, 7/30-day averages, extremity classification). This clearly distinguishes it from any sibling tool by stating exactly what data is provided. The verb is implied ('provides' or 'retrieves'), but the purpose is unambiguous.

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 gives clear context about the tool's function, data source (alternative.me), and update frequency (daily). It does not explicitly mention when to use it vs alternatives or provide exclusions, but since no sibling tool serves the same index, the usage is well-implied. It lacks explicit 'when not to use' guidance, which prevents a 5.

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