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

No annotations are provided, so the description carries the full burden of disclosing behavior and side effects. The text only repeats the name and reveals nothing about what the tool returns, whether it requires network access, what date formats are accepted, or what moon phase information is produced. This is a complete behavioral void.

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 extremely short, but this is under-specification rather than effective conciseness. 'Moon Phase: Moon Phase' contains zero informational value and does not earn its place as a functional description. A concise description would state the action and result, not repeat the title.

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?

Even for a simple one-parameter tool, the description omits essential context: what output the agent should expect, the date format to use, and whether the result is a phase name, emoji, percentage, or something else. With no output schema and no annotations, this description is inadequate for an agent to call the tool confidently.

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?

Schema description coverage is 100% because the only parameter, 'date', has the description 'Date to process'. The tool description adds no additional meaning beyond this, but the baseline of 3 applies when the schema already documents the parameters. The date format itself remains unspecified, but that gap is not compensated by the description.

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 is 'Moon Phase: Moon Phase', which merely restates the tool name without adding any functional meaning. It does not use a specific verb, state what the tool computes, or distinguish it from any sibling tool. This is a tautology rather than a purpose statement.

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 no guidance on when to use this tool versus alternatives such as date, calendar, or astronomy utilities. It neither implies a usage context nor names any exclusions or sibling alternatives. The agent is left entirely without direction for selection.

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