List Available Library Sources

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

Annotations already cover read-only, idempotent, non-destructive behavior. The description adds meaningful behavioral context beyond that: the source count of 152 is computed dynamically from the live registry at startup, so it may change between runs. It also signals that the response is a complete enumeration rather than a paginated or filtered subset.

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?

A single front-loaded sentence conveys the action, the full scope, the count, and the returned detail level. The parenthetical about the live registry is compact and adds value without wasting space.

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 parameterless list tool, the description is complete: it states what is listed, how much is listed, and what information each entry carries. Combined with the output schema and annotations, an agent has everything needed to invoke and interpret the tool 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?

The tool has zero parameters, so the description does not need to explain parameter usage. The baseline of 4 applies because there is no parameter burden for the description to carry.

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 states a specific verb and resource: 'List all 152 library sources' with the content of the listing ('descriptions and capabilities'). This clearly distinguishes it from siblings like library_search or library_read, which operate on content rather than enumerating sources.

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 intended use case is implied—use this to discover the full set of available library sources before selecting one—but there is no explicit when-to-use, when-not-to-use, or mention of alternatives. The description is sufficient for the obvious listing purpose, but it does not actively route the agent away from sibling tools.

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