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

Annotations already declare readOnlyHint=true, destructiveHint=false and openWorldHint=true, so the safety profile is covered. The description adds value the annotations don't: it names the payload contents (subject, HTML and text bodies), which matters because there is no output schema, and it maps the call to GET /messages/{messageId}.

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 sentences, zero filler. The return content is front-loaded ahead of the endpoint mapping, so the agent gets the useful information first.

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 one-parameter read tool with full annotation coverage and full schema coverage, this is nearly complete: it says what it returns and how it maps to the API. Only edge behavior such as not-found handling is unaddressed, which is minor here.

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 a single documented integer message_id, so the schema carries parameter meaning. The description only reinforces that lookup is by id and supplies the path template; it adds no format or validation detail beyond the schema.

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 ('One message by id') plus the fields returned, which distinguishes it from list_messages and get_message_statistics. It stops short of naming those siblings explicitly, but the singular-by-id framing makes the distinction clear.

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?

Usage is only implied: the phrase 'One message by id' suggests fetching a known message rather than browsing, but the description never says when to use this versus icontact_list_messages or icontact_get_message_statistics, and states no prerequisites.

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