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

No annotations are provided, so the description carries the full burden. It discloses meaningful behavior: the effect on unread_only inbox queries and that receipts are per-recipient and invisible to the sender. It does not state idempotency, whether marking nonexistent IDs errors, or auth beyond what the schema conveys.

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?

Three compact clauses, front-loaded with the core action, then the behavioral consequence, then the scoping rule. Every sentence earns its place with no padding.

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 two-parameter mutation tool with no annotations and no output schema, the description covers the essential semantics (effect and scoping) but omits return behavior, error cases, and idempotency. Adequate but with clear gaps given the lack of structured behavioral data.

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 both parameters are already documented in the schema. The description adds only the per-recipient framing ('for you'), which is consistent with but not richer than the schema's 'mark read for you.' Baseline 3 applies when the schema does the heavy lifting.

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?

Clear verb+resource: 'Mark messages as read for you.' It states the effect on the inbox (unread_only reads stop returning them) and the per-recipient scoping. It doesn't explicitly distinguish from siblings like host.msg.inbox or host.msg.thread, but the read-receipt semantics make its domain unambiguous.

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 implied by the behavioral note that unread_only inbox reads stop returning marked messages, which tells the agent the consequence of calling it. However, there is no explicit when-to-use vs when-not-to-use guidance or named alternative (e.g., host.msg.inbox for reading).

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