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

Annotations already declare readOnlyHint=true, openWorldHint=true, and destructiveHint=false, so the safety profile is covered. The description adds the useful non-obvious fact that each call costs 1 credit, but says nothing about output shape or error behavior. With annotations carrying the behavioral burden, a 3 is appropriate.

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 compact clauses: purpose first, cost second. No filler, no redundant restatement beyond the unavoidable title echo.

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?

An output schema exists, so return values need not be explained, and the tool is simple. However, the description omits the decode direction's parameter value and gives no hint about input constraints beyond what the schema states, leaving a small but real gap for correct invocation.

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%, so the schema already documents both parameters, and 'between Unicode and Punycode' only implies the direction. Notably, the description does not clarify that the mode parameter accepts a 'decode' value, since the schema shows only the default and an 'encode' example, leaving the reverse value undocumented.

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 names a specific verb and resource ('Convert between Unicode and Punycode') and scopes it to internationalized domain names. It is clear what the tool does, though it largely restates the title and does not explicitly distinguish itself from conversion siblings such as URLEncoderDecoder or UnicodeEscapeUnescape.

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?

There is no guidance on when to use this tool versus alternatives, and no prerequisites (e.g., that input should be a domain or a label). The only extra operative detail is the credit cost, which is not usage guidance.

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