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

Annotations already declare readOnly, idempotent, and non-destructive behavior. The description adds useful context in the form of the data source ('sunrise-sunset.org / Open-Meteo') and cost ('$0.005 per call'), but does not go further into response shape or rate limits. No contradiction with annotations.

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 extremely compact: one resource line, source, pricing, and endpoint, with no filler. Every element earns its place and key facts are front-loaded.

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, the description covers the output fields and source while annotations cover safety. The absence of an output schema is mitigated by listing the data fields explicitly; however, it does not clarify that q or lat/lon is needed (all schema fields are optional).

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% and every parameter has an example and description, so the description adds no parameter-level meaning beyond signaling the coordinate basis. Baseline 3 is appropriate because the schema already carries the semantic load.

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 specifies the resource ('Sunrise, sunset, solar noon, day length') and scope ('by coordinate'), which clearly distinguishes it from unrelated siblings like weather or timezone. It lacks an explicit verb such as 'get' or 'retrieve,' but the output list makes the action unambiguous.

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?

Usage is only implied: the description says the data is 'by coordinate,' so an agent can infer this is for solar timing queries, not for general weather or timezone. It names no alternatives, exclusions, or whether lat/lon vs q is preferred, leaving selection guidance implicit.

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