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

Annotations already declare readOnly, idempotent, non-destructive, closed-world, so the safety profile is covered. The description adds genuinely new behavioral context the annotations cannot: the output is rule-based with no generated text, and the spine-detection heuristic (books read on three or more consecutive Sundays, longest run named). It does not discuss cost or pagination, but none are implied here.

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 densely packed sentence, but front-loaded with the verb and date-range scope and ordered from per-Sunday facts to aggregate findings. No filler, no restatement of the title.

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?

There is no output schema, so the description must carry the return shape — and it does, naming every returned field group and the derived spine concept. Combined with 100% parameter coverage, an agent has everything needed to call and interpret the result.

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 all three parameters are already documented, including the focus enum and the weekday-to-next-Sunday rule. The description adds nothing parameter-specific beyond hinting that 'focus' narrows where the spine is sought, which the schema already states. Baseline 3 applies when the schema does the heavy lifting.

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 ('Lays out a run of Sundays from a start date') and then enumerates exactly what each Sunday carries: name, season, color, lectionary year, appointed readings, feasts, and book-runs. That enumeration distinguishes it from the single-date siblings (readings_for_sunday, season_for_date, upcoming_feast_days) without needing to name them.

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 implied by the composite output (planning a multi-Sunday series), but there is no explicit when-to-use statement and no routing guidance against the single-date siblings. An agent can infer this tool supersedes the siblings for a run, but must infer it rather than being told.

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