Get my saved (favorited) Zillow homes

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

Annotations already cover readOnly/idempotent/openWorld, and the description adds genuinely non-obvious behavior: an unknown session_id errors, and the id is a label only because the request goes through whichever tab the extension is signed into. That is exactly the kind of surprising routing detail annotations cannot express.

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?

Front-loaded with purpose and return contents, then the session_id caveat, then auth and safety notes. Every sentence carries information — notably the return-field list, which is needed because no output schema exists.

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?

With no output schema, the description compensates by enumerating returned fields, and it also documents the auth requirement and the session-id edge case. An agent has everything needed 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?

Schema coverage is 100%, so the baseline is 3, but the description adds real meaning beyond the schema: session_id is validated against a registry and errors if unknown, yet does not control routing and defaults to the active session. That is substantive semantic detail, not a restatement.

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 names a specific verb+resource (the signed-in user's saved/favorited homes) and adds scope precision ('flattened across all of the user's collections'), which cleanly separates it from zillow_get_saved_searches and the other zillow_get_* siblings.

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?

It states the precondition ('Requires the user to be signed in') and the safety profile ('Read-only; safe to call repeatedly'), giving clear context for when the tool applies. It never explicitly routes the agent away from an alternative such as zillow_get_saved_searches, so it stops short of the 5-level when/when-not guidance.

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