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

Annotations already mark it read-only, idempotent, and non-destructive. The description adds valuable behavioral context: 'reverse chronological order,' 'sender role (member, facility, agent),' 'cursor-based pagination,' and notably 'Automatically marks facility messages as read'—a side effect not covered by the annotations. This is transparent and does not contradict the annotations.

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 four sentences, all informative. It is front-loaded with the core action, then adds routing, ordering, sender roles, pagination, and the read side effect. No filler or redundant restatement of the tool name.

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?

Given the tool has an output schema (messages with sender roles) and only two optional parameters, the description covers all essential user-facing behavior: what it reads (message thread), ordering, pagination mechanism, and side effect (marks as read). The 'Facility routing is automatic' clause clarifies there is no need for a facility ID. This is complete for an agent to select and invoke the tool correctly.

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% (both 'limit' and 'before' have detailed descriptions). The description adds only general context about pagination ('cursor-based pagination') that reinforces, rather than extends, the schema. It does not provide deeper parameter semantics beyond what the schema already offers, so baseline 3 is appropriate.

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 starts with a specific verb+resource: 'Read the message thread with Austin HQ.' It clearly distinguishes from siblings like send_facility_message (write) and list_facility_conversations (list conversations, not messages). 'Facility routing is automatic' adds scope, making the tool's purpose unmistakable.

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 description clearly implies use for reading the facility message thread, not sending (send_facility_message) or listing conversations (list_facility_conversations). 'Facility routing is automatic' tells the agent no additional routing parameter is needed. However, it does not explicitly name alternative tools or state exclusions, so it stops short of a 5.

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