calendar_open

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

With no annotations at all, the description carries the full burden, and it does disclose the return shape (view, toolbar title, visible items, with per-day counts in month view) and that the view may be switched as a side effect. It omits whether the tool is read-only versus state-changing, whether it launches the app, and any latency or failure behavior, which matters for an unannotated UI-driving tool.

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?

Two tight sentences: what it does and returns first, the sibling alternative last. No filler, and the most important information is 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?

There is no output schema, but the description compensates by enumerating the return payload, including the month-view special case. For a 2-parameter, zero-required navigation tool this is nearly complete; only the app-state prerequisite is left unstated.

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 (date formats, view enum and its 'keep current view' default) are already fully documented. The description only alludes to the view parameter ('optionally switching view') without adding format or edge-case detail beyond the schema, so the baseline 3 applies.

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 ('Show a date') plus the resource (Calendar app), and adds the read-back behavior ('read what is visible'). It explicitly distinguishes itself from the sibling calendar_view_screen, so an agent can pick between them without opening either 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 an explicit routing rule: use this to open a date/view, use calendar_view_screen to read whole days in detail. That is a real when-to-use statement. It stops short of a full 5 because there is no guidance on prerequisites (must the Calendar app be running?) or when neither tool is appropriate.

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