Ferret

Lend, borrow, or change a loan

save_loan

Instructions

Records that one of the household's items was lent to someone (direction "lent") or that something was borrowed from them ("borrowed"), optionally with a due-back date — or, with id, changes an open loan (who has it, when it's due back, the note, the borrower's email and how often they're reminded). To add: itemId (from search_inventory), direction and person; an item has one open loan at a time. For it coming back use return_loan. Returns the loan with its id and due date.

Tool call template

This tool declares no required parameters. Add optional parameters from the input schema as needed.

{
  "id": 1,
  "jsonrpc": "2.0",
  "method": "tools/call",
  "params": {
    "arguments": {},
    "name": "save_loan"
  }
}

Input Schema

Name	Required	Description
`id`	No	The loan to change, from list_loans; leave out to add a new one
`note`	No	Anything worth remembering about the loan
`dueOn`	No	When it's due back, yyyy-mm-dd
`email`	No	Lent: the borrower's email, for reminders
`since`	No	When it went (or came), yyyy-mm-dd; today if left out
`itemId`	No	To add: the item's id, from search_inventory
`person`	No	Who has it (lent) or whose it is (borrowed)
`direction`	No	To add: "lent" (the household's thing is with someone) or "borrowed" (someone else's thing is here)
`remindEvery`	No	Lent, with an email: remind the borrower this often

Schema Changelog

Changes observed during successful MCP inspections.

Addedv2026.11.10Nov 9, 2026

TDQS

A4.3/5.0

Behavior4/5

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

Annotations only declare non-read-only, non-destructive, closed-world; the description adds valuable behavior: the mode switch on 'id', the one-open-loan-per-item invariant, and the return value ('the loan with its id and due date'). It stops short of saying whether omitted fields are left unchanged on update, or what validation failures look like for a mutation tool with no output schema.

Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.

Conciseness4/5

Is the description appropriately sized, front-loaded, and free of redundancy?

Front-loaded with the primary action, then the update branch, then the add recipe and the sibling pointer — a sensible priority order with no filler. The opening sentence is long and parenthetical-heavy, which costs a little readability, but every clause carries information.

Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.

Completeness4/5

Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?

For a 9-parameter, enum-bearing mutation tool with no output schema, the description covers the two operating modes, the key invariant, and what is returned. The remaining gap is update semantics for partially supplied fields, which matters given zero required parameters and optional nullability across most fields.

Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.

Parameters4/5

Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?

Schema coverage is 100%, so baseline is 3, and the description earns a bump by adding cross-parameter meaning the schema cannot express: id present means update versus absent means add, and the add path requires itemId + direction + person together. It does not elaborate on dueOn/since defaults or the remindEvery pairing with email beyond the schema's own wording.

Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.

Purpose5/5

Does the description clearly state what the tool does and how it differs from similar tools?

The description names a specific verb and resource ('Records that one of the household's items was lent…') and covers both modes explicitly: creation without 'id' and mutation with 'id'. It also names the sibling it is not ('For it coming back use return_loan'), so an agent can distinguish it from return_loan and list_loans without opening any schema.

Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.

Usage Guidelines4/5

Does the description explain when to use this tool, when not to, or what alternatives exist?

It gives concrete prerequisites for the add path ('itemId (from search_inventory), direction and person') and an explicit alternative for the return case. It also states a real constraint ('an item has one open loan at a time'). What it omits is how to delete or cancel a loan, and it does not spell out when to prefer an update via 'id' over creating a new record beyond the implicit 'with id' phrasing.

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