List Active Notebooks

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

No annotations are provided, so the description carries the full burden and meets it: it discloses server-side binding state, how that state is keyed (MCP session identity), and the non-obvious client-dependent caveat that makes the binding unreliable. This is exactly the kind of stateful side effect an agent could not infer from the name or schema.

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?

Purpose is front-loaded in a single short sentence, followed by return contents and then the binding caveat. The third paragraph is dense and version-specific, but each sentence carries load-bearing information about when the binding fails, so the length is justified rather than padding.

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?

An output schema exists, so return values need not be explained, yet the description briefly summarizes them (file paths and session IDs). Combined with the binding semantics and the client caveat, an agent has everything needed to call this correctly and to know what happens on the next call.

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% and there is only one optional parameter, so the baseline is 3. The description earns an extra point by explaining the behavioral consequence of omitting `server_url` — it ties omission to the auto-binding of the first discovered session, which the schema's "discovers servers from the marimo registry" note does not convey.

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 first sentence names a specific verb and resource ("List currently active marimo notebooks") and is the only discovery/listing tool among siblings dominated by cell/notebook mutation and inspection tools. An agent can distinguish it immediately without opening the schema.

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 calling pattern explicitly: the first discovered session is auto-bound, so subsequent calls may omit `session_id` and `server_url`. It goes further and names the condition under which that optimization fails (fastmcp's own Client on pinned fastmcp 4.0.3 negotiating a new MCP session per request), telling the agent exactly when to pass both parameters explicitly.

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