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

Annotations already declare readOnlyHint, idempotentHint, and destructiveHint. The description adds valuable behavioral context beyond that by specifying message types ('assistant text + tool calls') and ordering ('newest last'). It doesn't describe the exact return structure, but the added filter details are useful and do not contradict 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 two sentences long and every phrase earns its place: it states the action, the resource, the filtering criteria, the ordering, and the use case. No waste or redundancy.

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 simple read-only tool with 3 parameters and strong annotations, the description is mostly complete. It covers purpose, message types, ordering, and use context. Since there is no output schema, a more explicit mention of the return format (e.g., list of message objects) could improve clarity, but the description already implies a list of messages.

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%, and each parameter (case_id, run_id, limit) has its own description. The tool description does not add parameter-level meaning beyond what the schema already provides, so the baseline score of 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 uses the specific verb 'Return' and identifies the exact resource: 'latest qualifying messages (assistant text + tool calls) for a Run on a case'. It also specifies ordering ('newest last'), distinguishing it from the sibling listRunMessages which likely returns all messages.

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 provides clear context: 'Used to populate the live body of an active Run card in the case Activity timeline.' This tells an agent when to use it, but it does not explicitly name alternatives or say when not to use it.

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