list_existing_books

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

With no annotations, the description carries the full burden, but this is a zero-parameter read operation whose safety profile is self-evident from 'List'. It discloses the directory scope and the returned fields, yet says nothing about empty results, whether the directory is created if absent, or whether listing is paginated.

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 with no filler: verb, scope, and returned payload all land in one pass. Nothing could be removed without losing information.

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?

An output schema exists, so return values need no elaboration, and with no parameters and no annotations there is little else an agent needs. The only gap is the absence of any hint about when in the workflow to invoke it.

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 there is nothing for the description to document; the baseline for a parameterless tool is 4. The mention of BOOKS_OUTPUT_DIR is environmental context rather than a parameter, which is helpful but not required.

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?

States a specific verb ('List'), a specific resource ('bedtime picture-book projects'), and the exact scope ('in `BOOKS_OUTPUT_DIR`'), plus what each entry contains (HTML path, local URLs). No sibling tool in the list performs a discovery/list function, so there is no ambiguity to disambiguate.

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?

Usage is only implied — an agent can infer this is the discovery step before create_book_project or build_and_publish_book, but the description never says when to call it or that it should precede project creation. No exclusions or alternatives are given, and none exist among siblings.

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