check_in_library
Preferred. Accepts the widest URI mix (track, album, episode, show, audiobook, artist, user, playlist) in one request. Check whether items are saved in or followed by the user — this tests LIBRARY-SAVED/FOLLOWED state, distinct from check_following_artists which only tests artist FOLLOW state. Re...
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What check_in_library does on Spotify
AI agents call check_in_library to retrieve information from Spotify without modifying anything. It is typically the context-gathering step in research, monitoring, and reporting workflows, before the agent takes action elsewhere.
Why check_in_library is rated Low
Even though check_in_library only reads data, uncontrolled read access leaks sensitive information and racks up API costs: an agent caught in a retry loop can make thousands of calls a minute without anyone noticing.
Attacks that exploit this kind of access
The rule that runs check_in_library safely
PolicyLayer is an MCP gateway: it sits between your AI agents and Spotify, and checks every tool call against a rule you set before the call runs. Nothing changes on the server itself. For check_in_library, this is the rule to start with:
check_in_library is read-only, so it stays allowed. Everything else on the server is denied unless you say otherwise.
The button opens the PolicyLayer dashboard: create your workspace, connect Spotify, apply this rule, and every check_in_library call is checked against it from then on.
Questions about check_in_library
Preferred. Accepts the widest URI mix (track, album, episode, show, audiobook, artist, user, playlist) in one request. Check whether items are saved in or followed by the user — this tests LIBRARY-SAVED/FOLLOWED state, distinct from check_following_artists which only tests artist FOLLOW state. Returns a boolean per URI via Spotify. It is categorised as a Read tool in the Spotify MCP Server, which means it retrieves data without modifying state.
Register the Spotify MCP server in PolicyLayer and add a rule for check_in_library: allow, deny, rate-limit, or require approval. Point your MCP client at the PolicyLayer proxy URL and the rule is enforced on every call, before it reaches Spotify. Nothing to install.
check_in_library is a Read tool with low risk. Read-only tools are generally safe to allow by default.
Yes. Add a rate_limit block to the check_in_library rule in your PolicyLayer policy. For example, setting max: 10 and window: 60 limits the tool to 10 calls per minute. Rate limits are tracked per agent session and reset automatically.
Set action: deny in the PolicyLayer policy for check_in_library. The AI agent will receive a policy violation error and cannot call the tool. You can also include a reason field to explain why the tool is blocked.
check_in_library is provided by the Spotify MCP server (@novalux12/spotify-mcp). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.
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