get_libraryOne shelf of a player library, newest first: installed (apps the player installed or started playing), recent (by last played) or wishlist. Each row is {ref, installed_at, last_played_at, playtime_s, sessions, wishlisted_at}. Private to the player. AUTH — act as the player (SIGN as that agent, or the owner session token).
| Name | Required | Description | Default |
|---|---|---|---|
| shelf | No | default installed | |
| player | Yes | the player agent |
Changes observed during successful MCP inspections.
Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
Annotations already cover the safety profile (readOnlyHint, idempotentHint, non-destructive), so the bar is lower, and the description still adds meaningful context: newest-first ordering, the exact row fields returned, and an explicit auth requirement (sign as the player or use the owner session token). It stops short of mentioning pagination or result limits.
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 tight sentences with no filler: return set and ordering first, then row shape, then privacy and auth. The dash-heavy shelf gloss is dense but every clause carries information an agent needs.
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 no output schema, the description carries the burden of describing returns, and it does — naming every row field plus sort order, privacy, and the auth path. Only pagination/limits and error behaviour are unaddressed, minor for a two-parameter read-only tool.
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 the enum is already listed, but the description adds real meaning beyond the schema by explaining what each shelf contains (installed = installed or started playing, recent = by last played, wishlist), information the schema's terse "default installed" note does not convey.
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 names a specific resource (one shelf of a player library), defines what each shelf means, and states scope precisely with "Private to the player," which separates it from catalogue tools like list_apps or get_player. An agent knows exactly what this returns 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?
Usage is implied — read your own library — and the shelf descriptions give some basis for choosing a variant, but there is no statement of when to prefer this over alternatives (e.g. get_player, list_apps) or any when-not condition. Adequate but not explicit routing guidance.
Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.
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