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

Annotations already declare readOnly, idempotent, non-destructive, and closed-world, so the safety profile is covered. The description adds genuinely new behavior: the default resolves to today's date in US Eastern time when neither parameter is supplied. It leaves the precedence rule ambiguous if both 'day' and 'date' are passed.

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?

Front-loaded with the invocation condition, then inputs, then a worked example; every sentence carries information. Minor redundancy in enumerating return fields when an output schema already exists.

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 zero-required-parameter lookup with an output schema present, the description covers trigger, input formats, and default resolution. The one real gap is what happens when both 'day' and 'date' are supplied simultaneously.

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 both parameters are already documented, giving a baseline of 3. The description goes beyond that by explaining that the two inputs are alternatives and by documenting the zero-argument default timezone behavior, which is not expressed anywhere 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?

States a specific verb and resource ('look up ... one of the 90 days'), names the returned fields (date, Exodus reading, stage, opening prayer), and scopes the tool to a single program day so it is distinguishable from get_prayer and list_stages.

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?

'Call this when the user asks about the reading, date or stage for one of the 90 days' gives a concrete trigger condition, and the description covers the no-argument fallback. It stops short of naming alternatives (e.g., list_stages for the stage catalog) or stating exclusion conditions, so it does not reach the top band.

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