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 does meaningful work: it declares this is a write operation, that it costs no credits, and that it has no external side effect (no invites sent). It stops short of permissions, conflict/overlap behavior, or what is returned, so it is strong but not complete.

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 short sentences, zero filler, and the core action is front-loaded ahead of the constraints. Every sentence contributes a distinct fact (what it does, its cost/nature, its lack of side effects).

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 an unannotated create tool with no output schema, an agent still needs to know whether the created event's identifier is returned (so it can later update or delete it) and how lead_id changes behavior — neither is addressed. The cost and no-invites notes cover the most important gaps, leaving a middling but adequate 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 description coverage is only 57% (title, all_day, and description are undocumented), and the description adds nothing about any of the seven parameters — not even that lead_id is how you attach the event to a CRM record. At this coverage level the description should compensate and it does not.

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 ("Add a custom event to the CRM planner") and implicitly separates itself from meeting/invite tools by noting it only records on the internal calendar. It does not name its closest siblings (crm_update_calendar_event, crm_delete_calendar_event, crm_list_calendar_events), so the differentiation is inferential rather than explicit.

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?

The sentence "Does NOT send invites to anyone" gives one useful exclusion, steering agents away from this when they need to actually invite attendees. However, no positive trigger conditions, no prerequisites, and no named alternative (e.g. use crm_update_calendar_event to modify an existing event) are provided.

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