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igorgarbuz

Spotify MCP Node Server

by igorgarbuz

addTracksToPlaylist

Add multiple songs to a Spotify playlist using track IDs. Specify playlist ID and position for insertion.

Instructions

Add tracks to a Spotify playlist

Input Schema

TableJSON Schema
NameRequiredDescriptionDefault
playlistIdYesThe Spotify ID of the playlist
trackIdsYesArray of Spotify track IDs to add
positionNoPosition to insert the tracks (0-based index)

Implementation Reference

  • The handler function that adds tracks to a Spotify playlist by converting track IDs to URIs and calling the Spotify API's addItemsToPlaylist method.
      handler: async (args, extra: SpotifyHandlerExtra) => {
        const { playlistId, trackIds, position } = args;
    
        if (trackIds.length === 0) {
          return {
            content: [
              {
                type: 'text',
                text: 'Error: No track IDs provided',
              },
            ],
          };
        }
    
        try {
          const trackUris = trackIds.map((id) => `spotify:track:${id}`);
    
          await handleSpotifyRequest(async (spotifyApi) => {
            await spotifyApi.playlists.addItemsToPlaylist(
              playlistId,
              trackUris,
              position,
            );
          });
    
          return {
            content: [
              {
                type: 'text',
                text: `Successfully added ${trackIds.length} track${
                  trackIds.length === 1 ? '' : 's'
                } to playlist (ID: ${playlistId})`,
              },
            ],
          };
        } catch (error) {
          return {
            content: [
              {
                type: 'text',
                text: `Error adding tracks to playlist: ${
                  error instanceof Error ? error.message : String(error)
                }`,
              },
            ],
          };
        }
      },
    };
  • Zod schema defining the input parameters: playlistId (string), trackIds (array of strings), position (optional nonnegative number).
    schema: {
      playlistId: z.string().describe('The Spotify ID of the playlist'),
      trackIds: z.array(z.string()).describe('Array of Spotify track IDs to add'),
      position: z
        .number()
        .nonnegative()
        .optional()
        .describe('Position to insert the tracks (0-based index)'),
    },
  • src/write.ts:238-243 (registration)
    Exports the addTracksToPlaylist tool as part of the writeTools array.
    export const writeTools = [
      addToQueue,
      addTracksToPlaylist,
      createPlaylist,
      removeTracksFromPlaylist,
    ];
  • src/index.ts:12-14 (registration)
    Registers all tools from playTools, readTools, and writeTools (including addTracksToPlaylist) with the MCP server.
    [...playTools, ...readTools, ...writeTools].forEach((tool) => {
      server.tool(tool.name, tool.description, tool.schema, tool.handler);
    });
  • Uses the handleSpotifyRequest helper (imported from utils.ts) to perform the API call securely.
    await handleSpotifyRequest(async (spotifyApi) => {
      await spotifyApi.playlists.addItemsToPlaylist(
        playlistId,
        trackUris,
        position,
      );
    });
Behavior2/5

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

With no annotations provided, the description carries full burden for behavioral disclosure. It states the action ('Add tracks') but doesn't mention critical behaviors like whether this requires authentication, has rate limits, affects playlist ordering permanently, or returns any confirmation. For a mutation tool with zero annotation coverage, this is a significant gap in transparency.

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

Conciseness5/5

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

The description is a single, efficient sentence with zero wasted words. It's appropriately sized for the tool's complexity and front-loads the core purpose immediately, making it easy for an agent to parse quickly.

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

Completeness2/5

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

Given this is a mutation tool with no annotations and no output schema, the description is incomplete. It doesn't address authentication requirements, error conditions, response format, or how it differs from similar tools. For a tool that modifies user data, more contextual information is needed for safe and effective use.

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

Parameters3/5

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

Schema description coverage is 100%, so the schema already documents all three parameters thoroughly. The description adds no additional parameter semantics beyond what's in the schema (e.g., format examples, constraints, or usage tips), meeting the baseline score when schema does the heavy lifting.

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

Purpose4/5

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

The description clearly states the action ('Add tracks') and target resource ('to a Spotify playlist'), providing a specific verb+resource combination. However, it doesn't differentiate from sibling tools like 'addToQueue' or 'removeTracksFromPlaylist', which would require explicit comparison to earn a 5.

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

Usage Guidelines2/5

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

The description provides no guidance on when to use this tool versus alternatives like 'addToQueue' or 'createPlaylist'. It lacks any context about prerequisites (e.g., needing playlist ownership or premium subscription) or exclusions, leaving the agent to infer usage scenarios independently.

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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