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

Annotations only supply destructiveHint=true; the description earns its keep by explaining exactly what the destructive path is: is_note=false sends an email to the requester that 'cannot be unsent'. It also states the acting identity ('as the key's agent') and the underlying endpoint, going well beyond the annotation.

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?

Front-loads the core action, then the two-branch mode semantics, then the irreversibility warning and endpoint. Dense and largely waste-free; the trailing API path is informational but not strictly needed for selection, keeping it short of perfect.

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 a 4-param mutation tool with no output schema and only a destructiveHint annotation, the description covers identity, mode semantics, and the irreversible side effect. It omits what the call returns and does not restate format defaults, but those gaps are minor given the schema documents them.

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 baseline is 3. The description adds consequence-level meaning for the required is_note parameter (emailed vs internal, irreversibility) that the schema's terse one-liner does not convey, pushing it above baseline.

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 message to a ticket') and immediately differentiates the two modes the single tool supports: internal note vs emailed reply. An agent can distinguish it from siblings like deskpro_update_ticket or deskpro_list_ticket_messages without opening 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?

Gives clear mode-selection guidance via is_note=true vs false and the consequence of each. It does not compare against sibling tools (e.g., when to use update_ticket instead), but for a tool whose main ambiguity is note-vs-reply, the guidance is explicit and actionable.

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