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

No annotations are provided, so the description carries the full burden. It discloses that the tool works offline and lists the returned data (name, category, HTML entity). However, it does not explain how input is interpreted (e.g., whether 'q' expects a codepoint number, a character, or a string like 'U+1F600'), nor does it describe error behavior or edge cases. The offline note is a positive behavioral trait.

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 a single sentence with no filler. It front-loads the core purpose and includes a brief output list. However, it could add a short input-format hint without becoming verbose, so it is not a perfect 5.

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 are presumably defined there. The description covers the primary purpose and offline behavior. Missing are input format details and any prerequisites. For a simple lookup tool this might be adequate, but the ambiguity around 'q' makes it incomplete. The tool appears straightforward, so a 3 is fair.

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 0% description coverage for parameter 'q'. The description adds that it is a 'Unicode codepoint' but does not specify the expected format (decimal, hex, actual character, or escape sequence). This leaves the agent uncertain about how to construct a valid input. The description partially compensates but is insufficient.

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 looks up Unicode codepoints and returns name, category, and HTML entity. It is specific about the resource (Unicode codepoint) and the output fields. However, it does not explicitly differentiate itself from sibling tools like emoji or ascii85, which might also deal with character encodings. The 'offline' note adds a useful distinguishing characteristic.

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 no guidance on when to use this tool versus alternatives. Given the vast sibling list with related tools (emoji, base64, punycode), there is no mention of when unicode_lookup is preferable. It does not state any conditions or exclusions.

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