What is in this library

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

Annotations already declare readOnly, idempotent, non-destructive and closed-world, so the safety profile is covered. The description adds behavior beyond that: it is a cheap single-call operation and it functions as a capability probe for the rest of the toolset. What it does not add is anything about result size or shape, but the enumerated contents largely cover that.

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?

Two sentences, no filler. The first front-loads the returned contents and the second delivers the call-first directive and its justification, so each sentence 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?

With no output schema, the description carries the burden of telling the agent what comes back, and it does so by enumerating the reported dimensions. For a zero-parameter inventory tool with strong annotations, nothing needed for correct invocation is missing.

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 no parameters, so there is no parameter semantics to explain and the baseline applies. The description correctly focuses its words on the output inventory instead of inventing input guidance.

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 the resource (this library) and enumerates exactly what the tool reports: authority count, projects, tags, courts, captured source text volume, and snapshot age. That level of specificity distinguishes it from siblings like search_library and read_library_text, which operate on contents rather than describing the inventory.

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?

"Call this first. It costs one call and tells you which of the other tools can actually reach what you are after" gives explicit ordering advice and a concrete reason (cheap capability discovery) that steers the agent away from blind searching. It stops short of naming a specific sibling or a scenario where you would skip it, so it isn't full 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.