GrowthBook MCP Server

Instructions

Implementation Reference

• src/tools/features.ts:40-129 (handler)

  The handler function that executes the create_feature_flag tool: fetches environments, constructs payload, posts to GrowthBook API, handles response, and returns formatted content with links and code stubs.

  async ({
    id,
    valueType,
    defaultValue,
    description,
    project,
    fileExtension,
  }) => {
    // get environments
    let environments = [];
    const defaults = await getDefaults(apiKey, baseApiUrl);
    if (defaults.environments) {
      environments = defaults.environments;
    } else {
      const envRes = await fetch(
        `${baseApiUrl}/api/v1/features/environments`,
        {
          headers: {
            Authorization: `Bearer ${apiKey}`,
            "Content-Type": "application/json",
          },
        }
      );
      await handleResNotOk(envRes);
      const envData = await envRes.json();
      environments = envData.environments.map((env: any) => env.id);
    }
  
    const payload = {
      id,
      description,
      owner: user,
      valueType,
      defaultValue,
      tags: ["mcp"],
      environments: environments.reduce(
        (acc: Record<string, any>, env: string) => {
          acc[env] = {
            enabled: false,
            rules: [],
          };
          return acc;
        },
        {}
      ),
      ...(project && { project }),
    };
  
    try {
      const res = await fetch(`${baseApiUrl}/api/v1/features`, {
        method: "POST",
        headers: {
          Authorization: `Bearer ${apiKey}`,
          "Content-Type": "application/json",
        },
        body: JSON.stringify(payload),
      });
  
      await handleResNotOk(res);
  
      const data = await res.json();
      const { docs, language, stub } = getDocsMetadata(fileExtension);
      const linkToGrowthBook = generateLinkToGrowthBook(
        appOrigin,
        "features",
        id
      );
      const text = `This is the API response: ${JSON.stringify(data, null, 2)}
  
      Additionally, here is a template of what to show to the user:
  
      **✅ Your feature flag \`my-flag-name\` is ready!**
      [View it in GrowthBook](${linkToGrowthBook})
  
      **How to use it in your code:**
      (To the LLM agent. Use the text below to properly add the feature flag to the codebase. Also, surface the relevant docs/implemenation to the user)
  
      ${stub}
  
      **Want to learn more?**
      See the [GrowthBook ${language} docs](${docs})
    `;
  
      return {
        content: [{ type: "text", text }],
      };
    } catch (error) {
      throw new Error(`Error creating feature flag: ${error}`);
    }
  }

• src/tools/features.ts:22-130 (registration)

  Registers the create_feature_flag tool on the MCP server within registerFeatureTools, specifying name, description, input schema, hints, and handler function.

  /**
   * Tool: create_feature_flag
   */
  server.tool(
    "create_feature_flag",
    "Creates a new feature flag in GrowthBook and modifies the codebase when relevant.",
    {
      id: featureFlagSchema.id,
      valueType: featureFlagSchema.valueType,
      defaultValue: featureFlagSchema.defaultValue,
      description: featureFlagSchema.description.optional().default(""),
      project: featureFlagSchema.project.optional(),
      fileExtension: featureFlagSchema.fileExtension,
    },
    {
      readOnlyHint: false,
      destructiveHint: false,
    },
    async ({
      id,
      valueType,
      defaultValue,
      description,
      project,
      fileExtension,
    }) => {
      // get environments
      let environments = [];
      const defaults = await getDefaults(apiKey, baseApiUrl);
      if (defaults.environments) {
        environments = defaults.environments;
      } else {
        const envRes = await fetch(
          `${baseApiUrl}/api/v1/features/environments`,
          {
            headers: {
              Authorization: `Bearer ${apiKey}`,
              "Content-Type": "application/json",
            },
          }
        );
        await handleResNotOk(envRes);
        const envData = await envRes.json();
        environments = envData.environments.map((env: any) => env.id);
      }
  
      const payload = {
        id,
        description,
        owner: user,
        valueType,
        defaultValue,
        tags: ["mcp"],
        environments: environments.reduce(
          (acc: Record<string, any>, env: string) => {
            acc[env] = {
              enabled: false,
              rules: [],
            };
            return acc;
          },
          {}
        ),
        ...(project && { project }),
      };
  
      try {
        const res = await fetch(`${baseApiUrl}/api/v1/features`, {
          method: "POST",
          headers: {
            Authorization: `Bearer ${apiKey}`,
            "Content-Type": "application/json",
          },
          body: JSON.stringify(payload),
        });
  
        await handleResNotOk(res);
  
        const data = await res.json();
        const { docs, language, stub } = getDocsMetadata(fileExtension);
        const linkToGrowthBook = generateLinkToGrowthBook(
          appOrigin,
          "features",
          id
        );
        const text = `This is the API response: ${JSON.stringify(data, null, 2)}
  
        Additionally, here is a template of what to show to the user:
  
        **✅ Your feature flag \`my-flag-name\` is ready!**
        [View it in GrowthBook](${linkToGrowthBook})
  
        **How to use it in your code:**
        (To the LLM agent. Use the text below to properly add the feature flag to the codebase. Also, surface the relevant docs/implemenation to the user)
  
        ${stub}
  
        **Want to learn more?**
        See the [GrowthBook ${language} docs](${docs})
      `;
  
        return {
          content: [{ type: "text", text }],
        };
      } catch (error) {
        throw new Error(`Error creating feature flag: ${error}`);
      }
    }
  );

• src/utils.ts:240-263 (schema)

  Shared Zod schema object defining input parameters for feature flag tools, including id, valueType, defaultValue, etc.

  export const featureFlagSchema = {
    id: z
      .string()
      .regex(
        /^[a-zA-Z0-9_.:|_-]+$/,
        "Feature key can only include letters, numbers, and the characters _, -, ., :, and |"
      )
      .describe("A unique key name for the feature"),
    valueType: z
      .enum(["string", "number", "boolean", "json"])
      .describe("The value type the feature flag will return"),
    defaultValue: z.string().describe("The default value of the feature flag"),
    description: z.string().describe("A brief description of the feature flag"),
    archived: z.boolean().describe("Whether the feature flag should be archived"),
    project: z
      .string()
      .describe("The ID of the project to which the feature flag belongs"),
    // Contextual info
    fileExtension: z
      .enum(SUPPORTED_FILE_EXTENSIONS)
      .describe(
        "The extension of the current file. If it's unclear, ask the user."
      ),
  } as const;

• src/index.ts:81-87 (registration)

  Top-level call to registerFeatureTools in the main MCP server initialization, which includes the create_feature_flag tool.

  registerFeatureTools({
    server,
    baseApiUrl,
    apiKey,
    appOrigin,
    user,
  });