Set the active Zillow session

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

Annotations already indicate a mutating (readOnlyHint=false) and idempotent operation, and the description does not contradict that. It adds the key behavioral fact that this sets a default for later calls and that explicit per-call session ids take precedence. It doesn't discuss persistence or error behavior, but these are less critical given the simple semantics and idempotence annotation.

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 sentences, front-loaded with the core switching behavior, followed by the prerequisite and override rule. Every sentence adds necessary information 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 setter with annotations for mutation and idempotence, the description covers what the tool does, where the session_id comes from, and how it interacts with per-call overrides. The only minor gap is lack of explicit return-value or error semantics, but that is low-stakes for such a simple setter.

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 schema alone documents session_id as 'Session id to make active' and covers 100% of parameters. The description adds essential provenance: it must be a previously registered session from zillow_register_session. This extra context helps the agent supply a valid value rather than any arbitrary string.

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 ('Switch') and resource ('which registered session subsequent tool calls route through'), making the action unmistakable. It also distinguishes itself from session creation by requiring a previously registered session_id. No ambiguity with siblings like zillow_register_session.

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 states the exact use case: change the default routing for subsequent calls. It conditions the input on a session_id previously returned by zillow_register_session, telling the agent where to obtain a valid value. It further clarifies that explicit per-call session_id parameters override this default, which prevents misuse, though it does not explicitly enumerate when not to use the tool.

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