List libraries

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

The annotations already establish readOnly, idempotent, non-destructive, and closed-world behavior, so the description appropriately focuses on return-value semantics. It adds genuinely useful context annotations cannot provide: that each section includes a key, whether a scan is running (refreshing), and a warning about misleading type values. It does not, however, discuss ordering or performance.

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?

Four sentences are tightly packed with useful distinctions (libraryType vs type vs agent/scanner), and the core purpose leads. The agent/scanner aside is somewhat marginal, but it clarifies the source of the derived field rather than repeating the schema.

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?

There is no output schema and no parameters, so the description must supply the shape of the result on its own. It names the key fields (libraryType, key, refreshing) and explains the most dangerous ambiguity (movie scanner vs Other Videos). Only minor omissions such as section titles or ordering keep it below a 5.

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 tool takes zero parameters, so parameter semantics has no surface to cover. Rather than adding value here, the description spends its words on response fields, which is the baseline expected when no parameters exist.

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 opening sentence gives a specific verb and resource: 'List all Plex library sections.' It also defines the meaning of the returned libraryType field, so an agent knows exactly what the tool enumerates. It stops short of contrasting itself with the sibling library_stats, so a 4 rather than a 5.

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 says how to interpret the output ('libraryType is the field to read when deciding how to treat a library'), but it never says when to call this tool instead of library_stats, list_media, or search. Usage is implied by the broad enumeration rather than stated through explicit alternatives or exclusions.

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