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

Annotations declare the safety profile (not read-only, not destructive), and the description adds behavior they don't cover: the imported events actively block dates on charter.boats, the tool returns the stored source, and it does not itself fetch events immediately (sync_calendar does). That last nuance is genuinely useful, though nothing is said about duplicates, auth, or removal.

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 short clauses with zero filler; the core effect is front-loaded and the sibling pointer is appended compactly. Every clause carries information.

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?

With no output schema, the description usefully states what is returned ('the stored source'), and it discloses the calendar's blocking side effect. Missing only edge-case guidance (duplicates, re-adding, error conditions) for a mutation tool whose sibling remove_calendar exists.

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 100% (boat_id, source_url, source_name, source_type all documented), so the baseline is 3. The description adds no syntax or format detail beyond the schema, such as iCal URL constraints or the meaning of source_type.

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?

Names a specific verb (connect) and resource (external calendar), states the concrete effect ('its events block those dates on charter.boats'), and implicitly distinguishes itself from sync_calendar. An agent can identify the operation 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?

Identifies the complementary sibling and its role ('sync_calendar pulls it at once'), which tells the agent this is the setup step and sync is the follow-up. It doesn't spell out when-not-to-use or prerequisites (e.g., must the boat exist, can duplicates be added), so it stops short of full routing guidance.

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