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

Annotations carry only destructiveHint=true, so the description meaningfully adds that this mutates a real, user-visible calendar and that the same event_id overwrites the prior event. It stops short of disclosing whether omitted fields are cleared, whether attendee notifications are sent, or whether the operation is reversible.

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, front-loaded with the verb and the upsert semantics, with the destructive scope warning placed immediately after. The trailing API route is mildly redundant for an agent but cheap.

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 8-parameter mutation tool with no output schema and only a destructiveHint annotation, the description covers purpose, upsert semantics, and write target — enough to call it correctly. The notable gap is overwrite/partial-update behavior for optional fields, which an agent patching an existing event would want to know.

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%, so each of the 8 parameters is already documented in the schema, including event_id's upsert behavior and calendar_id's provenance. The description adds no format guidance (ISO 8601, tzid interaction) beyond what the schema supplies, so the baseline 3 is appropriate.

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 (upsert/create-or-update), the resource (event), and the critical scope constraint that it targets a REAL connected calendar, plus the exact API route. This clearly separates it from cronofy_read_events and cronofy_delete_event without needing to open any 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?

Explains the upsert contract — re-using event_id updates rather than duplicating — and warns that the write lands on the user's live calendar, which is the key context for deciding to call it. It does not, however, name any alternative or exclusion (e.g., use read_events to fetch before mutating) or state prerequisites like authorization scope.

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