List libraries

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

Annotations already declare readOnlyHint=true, so the agent knows this is a safe read operation. The description adds value by stating the access scope (libraries the API key's user can access), which is not derivable from annotations alone. It does not describe edge cases (e.g., empty results or error handling), but for a simple list tool, this is sufficient.

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 with no filler: the first states what the tool does, the second explains its importance for other tools. Every word earns its place.

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?

The tool has no output schema, but the description sufficiently describes return fields. With only one optional parameter fully documented in the schema, the description is complete for a simple list operation. The guidance to start here makes it contextually rich.

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%, and the schema already fully documents the detail parameter with its enum values and their effects. The description adds no parameter-specific meaning beyond what the schema provides. Baseline score of 3 is appropriate since the schema carries the full burden.

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 lists Audiobookshelf libraries accessible to the API key's user, and specifies the returned fields (id, name, media type). This distinguishes it from siblings like get_library (which likely targets a single library) and list_library_items (which lists items within a library).

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 explicitly says 'Start here — every other library tool needs a library id,' providing clear guidance on when to use this tool first and why it is a prerequisite for many other operations. This helps an AI agent understand the dependency chain.

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