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

Annotations already cover readOnly, idempotent and closed-world. The description adds genuine behavior beyond them: the latest-day default and the sign-derivation fallback when sign is omitted, which is non-obvious logic an agent needs.

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 sentences, front-loaded with the core action followed by defaults and fallback. No filler; every clause 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?

For a simple read-only lookup with no output schema and no required params, the description is sufficient: it covers the default date and the sign-derivation path. Only minor gap is that the return shape/format is unaddressed, though no output schema obligated it.

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 coverage is 100%, so baseline is 3. The description adds relational semantics the schema lists only individually: birthdate or agent_name are used to derive sign, and the sign is the primary selector. That cross-parameter dependency is real added value.

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?

States a specific verb and resource: 'Get the daily Astroclaw horoscope for a zodiac sign.' Clear what it does, though it never distinguishes itself from the siblings find_sign or list_signs, so an agent must infer the boundary.

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?

Gives clear operational context: defaults to the latest published day, and routes the agent to pass birthdate or agent_name when the sign is unknown. No explicit when-not-to-use or sibling comparison, but the fallback path is well communicated.

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