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

Annotations already declare readOnlyHint, idempotentHint, destructiveHint=false and openWorldHint=false, so the safety profile is covered. The description contributes genuinely new operational context — the endpoint (POST /v1/horizon) and the billing cost (50 credits, Tier 3) — which is useful for an agent weighing spend, but it says nothing about return shape or failure modes. With annotations carrying the safety 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?

One front-loaded sentence states the purpose, followed by compact bracketed metadata lines (group, endpoint, required, cost). Nothing is padded or repetitive, and the key clause comes first. The [Required] line is slightly redundant with the schema, keeping it from a 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?

The description establishes the operation and the endpoint/cost, and an output schema exists so return values need not be explained. However, for a 15-parameter tool with only 33% schema coverage, the description leaves most optional inputs (chart variant, zodiac type, house system, ayanamsa selection, compact-mode fields) entirely undiscussed, which is a 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 only 33% across 15 parameters, so the description needs to compensate and largely does not. It names only the four required parameters (date, time, latitude, longitude), which are already enforced by the schema's required array and therefore add no new meaning. The eleven optional parameters (zodiacType, houseSystem, ayanamsaId, cosmogram, city, name, etc.) receive no coverage in the description at all.

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 gives a specific verb (calculate) and a precise resource (azimuth and altitude of planets above the local horizon for a given time and location), which is markedly more informative than the vague 'Horizon Chart' title. It does not, however, distinguish this chart from the many sibling specialized chart tools (draconic, harmonics, heliocentric, vedic_divisional), so an agent cannot tell from the text alone which specialized chart fits a request.

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 when-to-use, when-not-to-use, or alternative-tool guidance. The bracketed [Required: ...] line merely restates the schema's required array, and [Cost: 50 credits] conveys pricing rather than a usage condition. Nothing tells the agent when a horizon chart is the right choice versus heliocentric or draconic.

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