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

readOnlyHint=true already tells the agent this is a safe read, so the safety bar is lowered. The description adds the returned field set and the 'must be an email message' precondition, but says nothing about behavior when the message is not an email (error vs empty), auth scope, or pagination — none of which is needed here given the single-resource read, but it is not rich either.

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 tightly packed sentences: the capability and its return fields come first, the constraint and endpoint second. No filler or restatement of the title.

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 carries the return-value burden and does so by naming the fields (HTML body, from, to, subject, Message-ID). The only gap is undefined behavior when the target message is not an email, which is minor given a simple two-id read.

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% with only two integer ids, so the schema fully documents the parameters. The description restates the required inputs only via the endpoint path (ticket_id, message_id) and adds no format or sourcing detail beyond that. 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 and resource ('Fetch the full email behind one message of a ticket') and enumerates what comes back: original HTML body, from, to, subject, Message-ID. This plainly distinguishes it from trengo_list_ticket_messages, which lists messages rather than retrieving one email's full payload.

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?

Implicit usage is derivable from 'behind one message of a ticket' and the constraint 'The message must be an email message,' but there is no explicit when-to-use guidance or named alternative (e.g., list_ticket_messages for non-email messages). Adequate at the minimum-viable level.

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