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

Annotations already cover the mutation profile (readOnlyHint=false, destructiveHint=false, not idempotent), so the description's added value is the key behavioral fact that a model interprets the free text rather than the caller naming ops. It omits what happens on failure or a version mismatch, so it stops short of full disclosure.

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?

Two tight sentences plus a docs link, with the differentiation from setAssistantItems front-loaded. Slightly dense with nested quotes, but nothing is wasted.

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 model-backed mutation with no output schema, the description covers what the tool does and when to use it but not the prerequisites (a session must already exist) or the meaning of expectedVersion. An agent can invoke it, but may not handle version conflicts or the assistant session lifecycle 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 0% across three required params. The quoted example ('that's right, drop the second, add photography') usefully conveys that instruction is natural-language text relative to a list, but sessionId and especially expectedVersion (an optimistic-concurrency token) are left completely unexplained.

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?

States a specific verb and resource (change a list) with a concrete input example, and explicitly separates itself from setAssistantItems. An agent can tell the two apart without opening either schema.

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?

Explicit routing rule: 'Prefer setAssistantItems when you can name the ops yourself; this one runs a model.' It names the alternative and the condition that selects it, which is exactly what usage guidance should do.

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