Start a Scoped Runtime Session

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

With all annotations false, the description carries the behavioral disclosure burden and does add substantial context: it reveals the session is isolated, the scope is immutable, and the budget is a hard between-action ceiling. This goes beyond the generic 'create session' phrasing and gives the agent meaningful expectations about side effects and restrictions.

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?

A single, dense sentence with no filler. Every element earns its place: the action, the object, the isolation property, and the key constraints. The most important information is front-loaded.

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 creation tool with 100% parameter schema coverage and an output schema available, the description covers the essential behavioral constraints and is sufficient for an agent to invoke it correctly. It does not discuss lifecycle details like whether multiple sessions can coexist or what happens on repeat calls, but those are largely covered by the output schema and the idempotentHint=false annotation.

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 the baseline is 3, but the description adds nuance by labeling the scope 'immutable' and the budget a 'hard between-action ceiling', which is more specific than the schema's 'Maximum cumulative metered cost'. These extra semantics clarify behavioral limits not captured in the parameter descriptions.

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 a specific verb ('Create') and a clear resource ('isolated capability session') with defining attributes: immutable scope, goal, retention period, and hard budget ceiling. It clearly stands apart from the sibling session-management tools, which read status, put context, or close sessions.

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 rather than explicit: an agent can infer that this tool is for starting a new session, but the description does not state when to use it versus alternatives, nor any prerequisites or exclusions. There is no mention of calling this before other session actions or of constraints like 'only one session at a time'.

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