Feature Flags Plugin

npm install @frontmcp/plugin-feature-flags

import { Tool, ToolContext } from '@frontmcp/sdk';
import { z } from '@frontmcp/sdk';

@Tool({
  name: 'beta-search',
  description: 'Search with beta features enabled',
  inputSchema: { query: z.string() },
  featureFlag: 'beta-search', // Hidden when flag is off
})
export default class BetaSearchTool extends ToolContext {
  async execute(input: { query: string }) {
    return `Beta results for: ${input.query}`;
  }
}

@Tool({
  name: 'smart-tool',
  description: 'A tool that adapts based on flags',
  inputSchema: { query: z.string() },
})
export default class SmartTool extends ToolContext {
  async execute(input: { query: string }) {
    const useBeta = await this.featureFlags.isEnabled('beta-algorithm');

    if (useBeta) {
      return this.betaSearch(input.query);
    }
    return this.standardSearch(input.query);
  }
}

FeatureFlagPlugin.init({
  adapter: 'static',
  flags: {
    'beta-search': true,
    'experimental-agent': false,
    'premium-feature': true,
  },
})

FeatureFlagPlugin.init({
  adapter: 'splitio',
  config: {
    apiKey: process.env.SPLITIO_API_KEY!,
  },
})

FeatureFlagPlugin.init({
  adapter: 'launchdarkly',
  config: {
    sdkKey: process.env.LAUNCHDARKLY_SDK_KEY!,
  },
})

FeatureFlagPlugin.init({
  adapter: 'unleash',
  config: {
    url: process.env.UNLEASH_URL!,
    appName: 'my-mcp-server',
    apiKey: process.env.UNLEASH_API_KEY,
  },
})

import type { FeatureFlagAdapter } from '@frontmcp/plugin-feature-flags';

const myAdapter: FeatureFlagAdapter = {
  async initialize() { /* connect to your service */ },
  async isEnabled(flagKey, context) {
    return await myService.checkFlag(flagKey, context.userId);
  },
  async getVariant(flagKey, context) {
    const variant = await myService.getVariant(flagKey, context.userId);
    return { name: variant.name, value: variant.value, enabled: variant.enabled };
  },
  async evaluateFlags(flagKeys, context) {
    const results = new Map<string, boolean>();
    for (const key of flagKeys) {
      results.set(key, await myService.checkFlag(key, context.userId));
    }
    return results;
  },
  async destroy() { /* cleanup */ },
};

FeatureFlagPlugin.init({
  adapter: 'custom',
  adapterInstance: myAdapter,
})

interface FeatureFlagAdapter {
  initialize(): Promise<void>;
  isEnabled(flagKey: string, context: FeatureFlagContext): Promise<boolean>;
  getVariant(flagKey: string, context: FeatureFlagContext): Promise<FeatureFlagVariant>;
  evaluateFlags(flagKeys: string[], context: FeatureFlagContext): Promise<Map<string, boolean>>;
  destroy(): Promise<void>;
}

@Tool({ name: 'beta-search', featureFlag: 'beta-search' })
@Resource({ uri: 'data://beta', featureFlag: 'beta-data' })
@ResourceTemplate({ name: 'beta-reports', uriTemplate: 'reports://beta/{id}', featureFlag: 'beta-reports' })
@Prompt({ name: 'beta-prompt', featureFlag: 'beta-prompt' })
@Skill({ name: 'beta-skill', featureFlag: 'beta-skill' })

@Tool({
  name: 'critical-tool',
  featureFlag: { key: 'critical-tool', defaultValue: true }, // fail-open
})

import { FrontMcp, App, Tool, ToolContext, Resource, ResourceContext, Prompt, PromptContext } from '@frontmcp/sdk';
import { FeatureFlagPlugin } from '@frontmcp/plugin-feature-flags';
import { z } from '@frontmcp/sdk';

// Configure with static adapter
const featureFlagPlugin = FeatureFlagPlugin.init({
  adapter: 'static',
  flags: {
    'beta-search': true,
    'experimental-agent': false,
    'premium-reports': true,
  },
  defaultValue: false,
});

// Tool gated by a feature flag
@Tool({
  name: 'beta-search',
  description: 'Search with beta algorithm',
  inputSchema: { query: z.string() },
  featureFlag: 'beta-search',
})
class BetaSearchTool extends ToolContext {
  async execute(input: { query: string }) {
    return `Beta results for: ${input.query}`;
  }
}

// Tool with fail-open behavior
@Tool({
  name: 'always-on-tool',
  description: 'A tool that defaults to enabled',
  inputSchema: { input: z.string() },
  featureFlag: { key: 'always-on', defaultValue: true },
})
class AlwaysOnTool extends ToolContext {
  async execute(input: { input: string }) {
    return `Processed: ${input.input}`;
  }
}

// Tool with programmatic flag check
@Tool({
  name: 'adaptive-tool',
  description: 'Adapts behavior based on flags',
  inputSchema: { data: z.string() },
})
class AdaptiveTool extends ToolContext {
  async execute(input: { data: string }) {
    const usePremium = await this.featureFlags.isEnabled('premium-reports');

    if (usePremium) {
      return `Premium report for: ${input.data}`;
    }
    return `Standard report for: ${input.data}`;
  }
}

// Resource gated by feature flag
@Resource({
  uri: 'report://premium-status',
  name: 'Premium Status Report',
  featureFlag: 'premium-reports',
})
class PremiumStatusResource extends ResourceContext {
  async read() {
    return { contents: [{ uri: 'report://premium-status', text: 'Premium data...' }] };
  }
}

// Prompt gated by feature flag
@Prompt({
  name: 'experimental-analysis',
  description: 'Experimental analysis prompt',
  featureFlag: 'experimental-agent',
})
class ExperimentalPrompt extends PromptContext {
  async execute() {
    return { messages: [{ role: 'user' as const, content: { type: 'text' as const, text: 'Analyze...' } }] };
  }
}

@App({
  id: 'flagged-app',
  name: 'Flagged App',
  plugins: [featureFlagPlugin],
  tools: [BetaSearchTool, AlwaysOnTool, AdaptiveTool],
  resources: [PremiumStatusResource],
  prompts: [ExperimentalPrompt],
})
class FlaggedApp {}

@FrontMcp({
  info: { name: 'Feature Flag Server', version: '1.0.0' },
  apps: [FlaggedApp],
  http: { port: 3000 },
})
export default class Server {}