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

Annotations already declare readOnlyHint and openWorldHint, so safety is covered. The description adds valuable context beyond that: default date is today in the city's local calendar, month=true expands to the whole month, and it lists what is returned (local times, UTC offset, Hijri date, calculation method, page URL).

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?

Three sentences, front-loaded with the resource and its fields, then location options, then date semantics and return values. Efficient, though the return-value enumeration is somewhat dense.

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?

Covers the location alternatives, date defaulting, month expansion, and return contents. With no output schema, describing the returned fields is appropriate. Missing only pagination/error behavior, which is minor for a single-record lookup.

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 the schema already defines parameters. The description adds meaning beyond the schema by clarifying slugs like "london-ca" for London, Ontario, noting city/place_id are alternatives, specifying local-calendar semantics for date, and explaining month's effect.

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+resource (prayer times for a city on a date) and enumerates the exact fields returned (Fajr, Sunrise, Dhuhr, Asr, Maghrib, Isha). The relationship to its sibling search_city is made explicit through the place_id reference.

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?

Explains the two mutually exclusive ways to identify a location (city slug or place_id) and points to search_city as the source of place_id. Lacks an explicit 'when to use this vs alternatives' exclusion, but for a single-purpose lookup tool the context is clear.

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