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

Annotations already declare readOnlyHint=true, but the description adds important behavioral context beyond annotations: it requires an API key for authentication, specifies how to send it, and explains that the tool reads the user's imported collection. It does not mention rate limits or error behavior but adds meaningful transparency about data source and auth.

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, front-loaded with the primary purpose, followed by a concise API key requirement with a URL. It is efficient, but the second sentence could be slightly more concise, and the informal 'what should I sleeve up tonight' adds color without critical information. Overall, it earns its place.

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?

The tool has an output schema and is read-only, so the description need not detail return values. However, it leaves unexplained key input parameters (limit, missing) and does not specify what 'most nearly build' means precisely. The auth requirement and purpose are clear, but without parameter semantics, completeness is only average.

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 input schema has 2 parameters (limit, missing) with zero description coverage. The description does not mention or explain these parameters at all. Given the low schema coverage, the description should compensate but fails to clarify what 'limit' or 'missing' control, leaving their semantics entirely ambiguous.

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 purpose: 'rank the Commander decks they can most nearly build right now' with 'the most-played cards they are still missing.' It distinguishes itself from siblings by focusing on deck suggestions from the user's collection, answering 'what should I sleeve up tonight'—a specific question different from card lookups, legality checks, or staples.

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 provides clear context for when to use the tool: 'Given the user's imported card collection' and 'from cards they physically have.' It implies use when a user wants deck recommendations based on their collection, but it does not explicitly contrast with sibling tools like 'upgrade_deck' or 'commander_staples,' so it lacks explicit exclusions.

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