session_new

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

With no annotations provided, the description carries the full burden of behavioral disclosure. It clearly states that the action creates an on-disk directory and explicitly clarifies it does not launch Chrome, which is valuable non-obvious behavior. However, it does not disclose other aspects like idempotency (what happens if the session already exists), whether the session becomes active, or any side effects on the current session state. The description is honest but sparse on behavioral detail.

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?

Single sentence with zero waste. The primary action is front-loaded, and the key clarification ('does NOT launch Chrome') is appended efficiently. Every word earns its place.

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?

This is a simple create operation with no output schema and full parameter documentation. The description clarifies the on-disk nature and the non-launch behavior, which covers the main ambiguity. Minor gaps remain, such as whether the created session becomes active or how to subsequently use it, but these can be inferred from sibling tools and the schema. Overall, sufficient for an agent to call it 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?

The input schema has 100% description coverage, with all three parameters documented. The description itself adds no parameter-specific information beyond the schema. Notable, the schema's session parameter already contains detailed guidance about using unique names for stateful work, so the description does not need to compensate. A baseline score of 3 is appropriate given the schema handles parameter semantics.

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 states a specific action ('Create'), a specific resource ('on-disk session/profile dir'), and adds a critical distinction ('does NOT launch Chrome') that differentiates it from the start tool and other launch-related siblings. This is precise and 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?

The description implicitly tells the agent this tool is for creating a session directory, not for launching a browser. However, it does not explicitly mention when to use it versus alternative session tools like session_use or session_switch, nor does it state conditions for when not to use it beyond the 'does NOT launch Chrome' note. Some guidance is implied but not fully articulated.

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