Register a signed-in Zillow session

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

The description adds significant behavioral context beyond the annotations: it explains idempotency (re-registering updates rather than duplicates), return value (session_id), default behavior (first session becomes active), and the mark_active parameter effect. Annotations already indicate idempotentHint=true, but the description enriches this with concrete behavior.

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 four sentences, each providing essential information: registration or refresh, idempotency, return value, default active behavior, and mark_active. No redundant or extraneous text.

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?

Given no output schema, the description adequately explains the return value (session_id) and the active session concept. It covers key aspects for a session registration tool. However, it could briefly mention that other tools require a registered session for authentication.

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% with each parameter documented. The description adds extra context: account_identity is typically an email, mark_active makes the session active immediately if true, and auth_expires_at is an optional expiration timestamp. It adds value beyond the schema's basic 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 specific verbs ('Register (or refresh)') and identifies the resource ('authenticated Zillow session'). It clearly distinguishes from sibling tools like zillow_set_active_session and zillow_get_session_context by explaining the tool's role in session creation and refresh, and mentions the returned session_id for routing calls.

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 clearly states the tool's purpose and how it fits into a workflow (first registered session becomes default active, mark_active parameter). However, it does not explicitly list alternatives or when not to use this tool, though sibling names imply other session management tools exist.

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