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

Annotations declare destructiveHint=true and idempotentHint=true, but the description adds substantial context beyond them: whole-series cancellation semantics, that already-sent/in-flight messages are silently refused with an explanatory result, and a per-call user-confirmation expectation. The free-plan note is minor but confirms availability rather than contradicting anything.

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?

Purpose and usage are front-loaded and efficient, but the return-value paragraph balloons into a deeply nested field dump (recipient → name_source enum → canonical_jid / phone_jid / lid_jid) that is hard to parse as prose. With no output schema this detail is defensible, but it should be structured or trimmed rather than crammed into one run-on sentence.

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, and the description compensates by documenting the return shape ({ cancelled, messages }) including the status enum and the distinction between series_id, occurrence and message_id. Combined with the destructive/idempotent annotations and the failure-case handling, an agent has everything needed to call this 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 100%, so the baseline is 3, and the description adds real meaning: 'if it repeats, the whole series is cancelled (any of the series' ids works)' — the 'any id in the series is acceptable' rule is not obvious from the schema's phrasing. Slight deduction because the id-format/source guidance is deferred to a sibling rather than stated here.

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?

Opens with a specific verb+resource ('Cancels scheduled messages before they are sent') and immediately distinguishes the scope: single message vs. an entire repeating series. An agent can tell it apart from delete_message and schedule_message 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?

Explicitly routes to siblings: 'Find ids with list_scheduled_messages (filter by `to` or `text`)' and 'To change a scheduled message, cancel it and schedule it again with schedule_message.' It also states the when-not case (already sent or in-flight can't be cancelled) and a confirmation policy ('Confirm with the user first unless they asked for it').

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