Extend a library loan by a specified number of days from its current due date, unless the loan is overdue, has no renewals left, or an active hold exists for the title.
Extend a loan by days from its current due date. Blocked if the
loan is overdue, out of renewals (2), or an active hold has that title.
| Name | Required | Description | Default |
|---|---|---|---|
| days | No | ||
| loan_id | Yes |
| Name | Required | Description | Default |
|---|---|---|---|
| result | Yes |
Changes observed during successful MCP inspections.
v0.1.0Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
With no annotations, the description carries the full burden and does disclose the key mutation semantics and preconditions that an agent must anticipate (overdue block, renewal cap of 2, hold conflict). It stops short of stating permission/auth requirements, whether the renewal is atomic or idempotent, or how a blocked attempt surfaces.
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 short sentences, front-loaded with the action, followed by the failure conditions. Nothing is redundant and no sentence could be cut 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 explanation, and the blocking conditions are fully covered for a two-parameter mutation. The only real omission is what happens to the remaining renewal count after a successful call.
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 0%, so the description must compensate, and it clarifies the non-obvious point that `days` counts from the current due date rather than today. `loan_id` is left to its self-explanatory name, which is a minor gap but not a blocking one.
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 states a specific verb and resource ('Extend a loan') plus the exact scope of the extension ('by `days` from its current due date'). This is clearly distinguishable from siblings like record_loan, return_loan, and update_hold 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.
Does the description explain when to use this tool, when not to, or what alternatives exist?
It gives explicit when-not conditions: the renewal is blocked if the loan is overdue, has exhausted its 2 renewals, or an active hold exists on the title. What it lacks is routing guidance to alternatives (e.g., which sibling to use instead when the loan is overdue).
Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.