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

Annotations already declare readOnlyHint/openWorldHint/destructiveHint, yet the description still adds real behavior: partial results surface in unavailable_sources instead of being silently treated as empty, reminders are keyed per item and that key is what planner_set_reminder consumes, dates are interpreted in the caller's IANA timezone, and results are scoped to the caller only. These are the details an agent needs to avoid misreporting an outage as an empty calendar.

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 verb, resource, and time bounds, then moves through data-shape caveats and parameter rules in one dense block. Every sentence carries information, though the long classification sentence ('distinguish interval events from ...') is packed enough that it reads as a run-on.

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?

No output schema exists, so the description carries the return-shape burden and does: unavailable_sources semantics, the reminders map and its item-key contract, and the exclusion of external_event imports. For a two-parameter read tool that is everything needed to call and interpret it correctly.

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 50% — `date` is documented in-schema but `days` is not. The description compensates by stating the date format and IANA timezone interpretation and that `days` defaults to 1 with a seven-day ceiling, which is the binding constraint an agent must respect. It stops short of examples (e.g. timezone offset edge cases) but meaningfully exceeds 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?

Specific verb and resource: 'Read the caller's combined Planner agenda and own busy intervals' with explicit scope ('a local calendar day or up to seven days'). It goes further and separates the returned item classes (interval events vs. free task deadlines, CRM follow-ups, reminders, and source=external_event calendar imports), so an agent can tell what will and will not appear without opening the schema.

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?

Gives a concrete triggering utterance ('what is on my day/week?') plus the day-cap condition, and clarifies which data sources are out of scope (external Google/Outlook/iCloud events). It does not route the agent to the closest siblings (planner_get_availability, planner_free_slots) when the caller actually wants availability rather than a listing, so guidance is clear but not fully exclusive.

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