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

The description aligns with annotations (readOnlyHint=true, destructiveHint=false) by indicating a read-only list operation. It adds context about uniqueness and applicability to the color filter, but doesn't disclose many behavioral details beyond that (e.g., ordering, errors), which is acceptable for a simple read-only endpoint.

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 two sentences, with the primary action in the first sentence and additional usage context in the second. No wasted words.

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?

As a simple, parameterless-required reference endpoint without an output schema, this description covers the purpose, return kind (list of unique colors), and primary use case. It's sufficiently complete for an AI agent to choose and invoke it 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 fully describes the only parameter `compact` with a clear explanation of its effects. The description doesn't add parameter information, but with 100% schema coverage, the baseline score of 3 applies.

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 clearly states the tool's function with a specific verb ('List all unique crystal colors') and explicitly distinguishes it from sibling tools by focusing on the color facet and connecting it to the GET /crystals color filter.

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 provides clear context for when to use this endpoint: to obtain color values for filtering crystals, and mentions use cases like building color-based browsing and pickers. It doesn't explicitly name alternatives, but sibling names make it clear that other facet tools exist for other filters.

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