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

Goes well past the annotations by disclosing a real-world side effect the hints cannot express: the file becomes un-deletable while attached. It also states the cost model ($0.01 per call, nothing on failure), which is behaviorally material for an agent deciding whether to retry.

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?

Three short sentences, each carrying distinct information: what it does, the persistence consequence, and the price. The primary action is front-loaded and nothing is redundant.

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 only two required params, no nesting, and no output schema, the definition covers purpose, precondition, side effect, and cost. The one gap is that nothing says what comes back on success (an attachment id or updated entry) or how partial failures behave, though the cost sentence partly addresses failure.

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% and both parameters are already documented, so the baseline is 3. The description only echoes the file source ("from the file store") that the schema already states, adding no format or constraint detail of its own.

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 (attach) and resource (a receipt or invoice file) plus the target (an entry) and the eligibility constraint (an entry that has none). None of the sibling books_* tools do this, and the wording makes the operation unmistakable without opening the schema.

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?

"to an entry that has none" gives an explicit precondition that tells the agent when this tool applies and implicitly when it will fail. It stops short of naming alternatives or describing what to do if the entry already has a receipt, so it falls one step below fully explicit routing.

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