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

The description adds the contextual detail 'by current user' beyond the annotations. However, it does not disclose potential side effects, such as whether already-read messages are skipped or whether the operation fails for invalid IDs. The readOnlyHint and destructiveHint are consistent with the described write-but-non-destructive behavior.

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?

The description is a single clear sentence with no unnecessary words. The schema is compact and directly focused on the single required parameter.

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?

The tool's purpose and parameters are well defined. While there is no output schema, the expected behavior of marking messages read is straightforward; no further context appears necessary for basic usage.

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?

The schema covers 100% of properties with descriptions. The top-level description explicitly clarifies that each array item is an object with an 'id', reinforcing the schema structure. No enums or nested objects add ambiguity.

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 clearly states the action ('Mark'), the target ('multiple messages'), the state change ('as read'), and the scope ('by current user'). This distinguishes it from singular variants like mark_message_read and other message actions such as mark_message_alerted.

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?

No explicit guidance on when to use this tool versus the singular mark_message_read. The plural 'multiple messages' in the description implies bulk usage, but no direct comparison or alternative mention is provided.

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