return_book

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

With no annotations provided, the description carries the full burden and does well: it states the side effect ('increases the book's available copy count by one'), records the return in member history, and discloses the error-handling behavior (errors returned as strings, never raised). This is rich behavioral disclosure for a mutation tool with zero annotation coverage.

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 appropriately sized at two sentences, front-loading the core action and then adding behavioral details. Every sentence earns its place. A minor improvement could be trimming, but it's tight and readable.

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?

The description covers side effects, error handling, and usage context. Since an output schema exists, the description needn't explain return values. It's complete for a two-parameter mutation tool given full schema coverage, though it could optionally clarify what happens on successful return (the output schema covers this).

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 (isbn, member_id) are already well documented in the schema itself. The description adds the error-returns-as-strings nuance and the 'M001' example format, providing marginal value beyond the schema but not requiring more given full schema coverage.

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 uses a specific verb+resource ('Return a previously borrowed book') and clearly states the scope ('on behalf of a library member'). It distinguishes itself from siblings by being the check-in counterpart to borrow_book, and the borrowing context is clearly established.

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 description explicitly states when to use the tool ('when the user wants to return / check in a book they have borrowed'), establishes clear context, and the sibling tools (borrow_book, search_books, check_availability) make the differentiation evident. It also clarifies behavior around required inputs.

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