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

Annotations already declare destructiveHint=true; the description earns credit by explaining why — the message is delivered to the customer on email/WhatsApp/chat and is irreversible. This is meaningful behavior beyond the annotation. It does not cover permission/auth requirements or rate limits, so not a 5.

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 sentences, front-loaded with the action and then the branching behavior and the irreversible-delivery warning. The API endpoint reference is a compact useful addendum. The all-caps emphasis is slightly heavy but functional.

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 5-param mutation tool with no output schema, the description covers the critical risk (irreversible customer-visible send) and both modes of operation. It does not need to explain return values, though it omits channel-specific pitfalls like HTML-only-for-email beyond what the schema states.

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 all five parameters (including internal_note's dual meaning and email-only subject/attachment_ids) are already documented in the schema. The description restates internal_note's semantics rather than adding new syntax or format detail, so baseline 3 applies.

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 ('Post a message on a ticket') and immediately splits the two modes of operation (internal note vs customer delivery), which is the key distinction an agent must make. It does not explicitly name a sibling, but the action is unambiguous against list_ticket_messages and the other ticket tools.

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 context for the two branches: internal_note=true for agents only, otherwise delivered to the customer's channel. Adds the operative caveat 'cannot be recalled — confirm the text first'. No explicit alternative tool is named, so it stops short of a 5.

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