Start a session

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

With no annotations, the description carries the full burden of behavioral disclosure. It reveals key behaviors: returns a sessionId, reuses an existing session, and establishes ordering. Minor gaps, such as side effects or persistence details, are not important for this simple initializer.

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, front-loaded with the key instruction ('Call this at the very beginning'), and every word adds value without repetition.

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 one-parameter tool with no output schema, the description is adequately complete. It explains when, what, and the idempotent behavior. Sibling tools are not confused with this one, and no additional context is necessary.

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 coverage is 100% for the single 'goal' parameter, and the schema description adds rich detail about how to provide the goal (in the user's own words, as an anchor). The tool description itself adds no extra parameter meaning, so the baseline of 3 applies.

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 clearly states the tool's purpose: starting a session and returning a sessionId. It distinguishes itself from sibling tools by explicitly mentioning that the sessionId is passed to every subsequent explain_change call.

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?

Explicitly instructs to call this tool at the very beginning of a task, providing clear timing. Also gives an alternative scenario: if an open session already exists, the existing session is returned, avoiding duplicate opens.

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