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

Annotations already cover readOnly, openWorld, idempotent, and destructive hints. The description adds the crucial 'does not mark it as read' behavior, which is not implied by the annotations. It also mentions attachment references, giving an extra expectation about the result. No contradiction exists.

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 that states the action, the identifier, the attachment note, and the side-effect note. Every clause earns its place, with zero filler.

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 read-only operation with a rich output schema and safety annotations, the description is nearly complete. It omits explicit pagination details, but bodyCursor is documented in the schema. The non-marking behavior and attachment references add important context. A 4 reflects that it covers essentials without being exhaustive.

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 the baseline is 3. The description reinforces the messageId's EPST nature but adds no additional meaning about bodyCursor, bodyFormat, or bodyMaxChars beyond what the schema already explains. It does not need to compensate.

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 states a clear verb ('Read') with a specific resource ('message') and identifier type ('EPST messageId'). It also adds the attachment references detail and the non-marking behavior, which distinguishes it from read_attachment and update_message siblings. No ambiguity remains.

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 usage context is clear: read a message when you have the EPST messageId. It does not explicitly mention alternatives or when not to use it, but the scope is self-evident and the sibling list does not introduce competing read tools that would require exclusion guidance.

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