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

Annotations already declare readOnly, idempotent, openWorld and non-destructive. The description adds genuinely new context beyond that: the service is free and requires no API key, and it enumerates the returned fields. No pagination/rate-limit detail, but meaningful added value over the annotations.

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 tight sentences; the capability statement is front-loaded and the usage hint follows. Slight redundancy between the return-fields list and the output schema, but no wasted prose.

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 simple two-parameter search tool with full schema coverage and an output schema, the description covers source, cost/access model, and return contents. The main omission is disambiguation from other book/text search tools.

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 description coverage is 100%, so both parameters (query and limit) are already documented with examples and bounds in the schema. The description adds nothing about parameter semantics, so the baseline 3 applies.

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 and resource ("Search Project Gutenberg's public-domain catalogue via Gutendex") and names the intermediary API, which lets an agent distinguish it from generic book-search siblings. It stops short of explicitly contrasting with overlapping tools like open_library_search or internet_archive_search.

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?

"Use to find free public-domain texts and their formats" implies the use case but gives no when-not guidance and names no alternative tool. Usage is inferable rather than explicit.

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