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

Annotations already cover read-only, idempotent, and closed-world behavior. The description adds substantial behavioral context beyond them: the search is case-insensitive substring only, not semantic/embedding search; it returns a snippet around the first hit; listing returns specific item metadata including an indexed flag; and unindexed items are invisible until indexed.

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 front-loaded with the core action and scope, then cleanly splits with-query and without-query behavior, and ends with a practical troubleshooting note. Every sentence adds useful information with no filler.

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 adequately explains what listing returns and what search results contain. It also covers the critical operational limitation around indexed versus unindexed items, making it complete enough for an agent to call 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?

Schema coverage is 100%, so the baseline is 3. The description enriches the query parameter significantly by naming the searched fields (name, REF code, extracted text) and clarifying it is substring rather than semantic search. It also describes scope behavior, though it does not add parameter-specific meaning for organisationId beyond what the schema already says.

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: finding Reference Library items, with clear scope (org-scoped items plus projects the caller is a member of). It distinguishes its two modes of operation, with and without a query, and clearly sets it apart from indexing siblings by explaining that search only covers already-indexed text.

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 gives explicit when-to-use guidance for both modes: use with a query for keyword search, omit the query to list every accessible item. It also provides a concrete troubleshooting path for empty search results, naming traceable_library_index as the action that makes unindexed items visible.

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