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

Annotations declare readOnlyHint=true, so the read-only nature is already covered. The description adds a bit of useful context by naming the exact output facets (HTML, text, subject) and the 'rendered' nature. It doesn't disclose edge-case behavior such as behavior for unsent messages or errors, but this is a simple read operation with the safety profile already captured.

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?

A single, front-loaded sentence with zero filler. Every word adds information: the action, the resource type, the exact data returned, and the lifecycle constraint.

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-only tool with no output schema, the description covers the essential purpose and the target object. It could have mentioned the response format or how to handle missing messages, but given the low complexity, nothing critical is missing.

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 message_id parameter is already documented in the schema. The tool description adds only the lifecycle context ('previously sent message'), which slightly enriches what message_id refers to, but does not introduce format, type, or usage details beyond the schema. 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?

The description uses a specific verb ('Get') and identifies a distinct resource: 'rendered content (HTML, text, subject) of a previously sent message.' It clearly differentiates from siblings like get_message, get_message_history, and get_notification_content by specifying the exact payload and lifecycle stage.

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?

The phrase 'previously sent message' provides clear context for when to invoke this tool—only for messages that have already been sent—but it does not explicitly exclude alternatives or reference sibling tools. It stops short of demonstrating full routing logic, though the context is unambiguous.

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