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

The annotations already establish readOnlyHint=true and destructiveHint=false, and the description stays consistent with those. It adds useful behavioral detail beyond the annotations: the six relations are mutually exclusive by construction, exactly one applies to any pair, a phase is returned only where branches combine, and the output includes a composed reading with strengths, frictions, and advice.

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 four focused sentences with no filler. It front-loads the purpose and method, then packs return semantics, exclusivity, and use cases into the remaining sentences, with every sentence earning 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?

For a read-only tool with four flat parameters, a fully documented schema, and no output schema, the description gives enough return-shaped context: relation, score, phase conditionally, and a composed reading. A precise JSON response shape is not specified, but the absence is minor given the clarity of the described outputs.

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 baseline is appropriately 3. The description does not add much parameter-level meaning beyond identifying the input as two Chinese zodiac animals, but it does not need to because sign1, sign2, lang, and compact are all well-documented in the schema.

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 action (score and explain), a specific resource (the relationship between two Chinese zodiac animals), and a distinct method (classical branch relations rather than a lookup table of opinions). It lists the concrete outputs and clarifies that exactly one of six mutually exclusive relations applies, making the tool easy to tell apart from sibling compatibility tools.

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 clear intended contexts: matchmaking features, relationship reports, and compatibility widgets. It also contrasts itself with lookup-table-based opinion tools, but it does not explicitly say when not to use it or name an alternative such as bazi compatibility, so some exclusion guidance is left implicit.

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