Reddit MCP Server

Instructions

Implementation Reference

• src/tools/post-tools.ts:212-257 (handler)

  The main tool handler function for 'reply_to_post'. It extracts parameters, gets the Reddit client, calls client.replyToPost, formats the comment info, and returns a success response with details.

  export async function replyToPost(params: {
    post_id: string;
    content: string;
    subreddit?: string;
  }) {
    const { post_id, content, subreddit } = params;
    const client = getRedditClient();
  
    if (!client) {
      throw new McpError(
        ErrorCode.InternalError,
        "Reddit client not initialized"
      );
    }
  
    try {
      console.log(`[Tool] Replying to post ${post_id}`);
      const comment = await client.replyToPost(post_id, content);
      const formattedComment = formatCommentInfo(comment);
  
      return {
        content: [
          {
            type: "text",
            text: `
  # Reply Posted Successfully
  
  ## Comment Details
  - Author: u/${formattedComment.author}
  - Subreddit: r/${formattedComment.context.subreddit}
  - Thread: ${formattedComment.context.thread}
  - Link: ${formattedComment.link}
  
  Your reply has been successfully posted.
            `,
          },
        ],
      };
    } catch (error) {
      console.error(`[Error] Error replying to post: ${error}`);
      throw new McpError(
        ErrorCode.InternalError,
        `Failed to reply to post: ${error}`
      );
    }
  }

• src/index.ts:209-229 (schema)

  The input schema and metadata for the 'reply_to_post' tool as registered in the listTools response.

    name: "reply_to_post",
    description: "Post a reply to an existing Reddit post",
    inputSchema: {
      type: "object",
      properties: {
        post_id: {
          type: "string",
          description: "The ID of the post to reply to",
        },
        content: {
          type: "string",
          description: "The content of the reply",
        },
        subreddit: {
          type: "string",
          description: "The subreddit name if known (for validation)",
        },
      },
      required: ["post_id", "content"],
    },
  },

• src/index.ts:464-471 (registration)

  The switch case in the CallToolRequest handler that dispatches 'reply_to_post' calls to the tools.replyToPost function.

  case "reply_to_post":
    return await tools.replyToPost(
      toolParams as {
        post_id: string;
        content: string;
        subreddit?: string;
      }
    );

• src/client/reddit-client.ts:364-407 (helper)

  The core RedditClient.replyToPost method that authenticates, checks post existence, makes the API POST to /api/comment, and constructs the RedditComment response object.

  async replyToPost(postId: string, content: string): Promise<RedditComment> {
    await this.authenticate();
  
    if (!this.username || !this.password) {
      throw new Error("User authentication required for posting replies");
    }
  
    try {
      if (!(await this.checkPostExists(postId))) {
        throw new Error(
          `Post with ID ${postId} does not exist or is not accessible`
        );
      }
  
      const params = new URLSearchParams();
      params.append("thing_id", `t3_${postId}`);
      params.append("text", content);
  
      const response = await this.api.post("/api/comment", params, {
        headers: {
          "Content-Type": "application/x-www-form-urlencoded",
        },
      });
  
      // Extract comment data from response
      const commentData = response.data;
      return {
        id: commentData.id,
        author: this.username,
        body: content,
        score: 1,
        controversiality: 0,
        subreddit: commentData.subreddit,
        submissionTitle: commentData.link_title,
        createdUtc: Date.now() / 1000,
        edited: false,
        isSubmitter: false,
        permalink: commentData.permalink,
      };
    } catch (error) {
      console.error(`[Error] Failed to reply to post ${postId}:`, error);
      throw new Error(`Failed to reply to post ${postId}`);
    }
  }