CanIUse MCP

Instructions

Implementation Reference

• src/enhanced-tools.js:185-328 (handler)

  The handleManageConfig function that executes the manage_config tool logic, dispatching to different configuration actions using the ConfigManager class.
  export async function handleManageConfig(args) { const { action = 'view', baseline, polyfill, feature, override, targetName, browser, version } = args; try { switch (action) { case 'view': const config = await configManager.loadConfig(); const targets = await configManager.getBrowserTargets(); return { action: 'view', currentConfig: { defaultBaseline: config.defaultBaseline, polyfills: config.polyfills, overrides: config.overrides, customTargets: config.customTargets }, availableTargets: Object.keys(targets), instructions: { setBaseline: 'Use action="set_baseline" with baseline="chrome-57"', addPolyfill: 'Use action="add_polyfill" with polyfill="css-grid"', removePolyfill: 'Use action="remove_polyfill" with polyfill="css-grid"', setOverride: 'Use action="set_override" with feature="css-variables" and override="supported"', addTarget: 'Use action="add_target" with targetName="chrome-57", browser="chrome", version="57"', createTemplate: 'Use action="create_template" to create .caniuse-config.json file' } }; case 'set_baseline': if (!baseline) { throw new Error('baseline parameter required for set_baseline action'); } await configManager.updateConfig({ defaultBaseline: baseline }); return { action: 'set_baseline', success: true, message: `Default baseline set to ${baseline}`, newBaseline: baseline }; case 'add_polyfill': if (!polyfill) { throw new Error('polyfill parameter required for add_polyfill action'); } await configManager.addPolyfill(polyfill); const updatedConfig = await configManager.loadConfig(); return { action: 'add_polyfill', success: true, message: `Added ${polyfill} to polyfills list`, feature: polyfill, currentPolyfills: updatedConfig.polyfills }; case 'remove_polyfill': if (!polyfill) { throw new Error('polyfill parameter required for remove_polyfill action'); } await configManager.removePolyfill(polyfill); const configAfterRemoval = await configManager.loadConfig(); return { action: 'remove_polyfill', success: true, message: `Removed ${polyfill} from polyfills list`, feature: polyfill, currentPolyfills: configAfterRemoval.polyfills }; case 'set_override': if (!feature || !override) { throw new Error('feature and override parameters required for set_override action'); } await configManager.setFeatureOverride(feature, override); return { action: 'set_override', success: true, message: `Set ${feature} override to ${override}`, feature, override }; case 'add_target': if (!targetName || !browser || !version) { throw new Error('targetName, browser, and version parameters required for add_target action'); } const currentConfig = await configManager.loadConfig(); const newCustomTargets = { ...currentConfig.customTargets, [targetName]: { browser, version } }; await configManager.updateConfig({ customTargets: newCustomTargets }); return { action: 'add_target', success: true, message: `Added custom target ${targetName} (${browser} ${version})`, targetName, browserConfig: { browser, version } }; case 'create_template': const templatePath = await ConfigManager.createConfigTemplate('.'); return { action: 'create_template', success: true, message: 'Created .caniuse-config.json template file', configFile: templatePath, instructions: [ 'Edit the created .caniuse-config.json file to customize your settings', 'Run manage_config with action="view" to see current configuration', 'The configuration will be automatically loaded for all compatibility checks' ] }; case 'reset': // Reset to default configuration await configManager.updateConfig({ defaultBaseline: 'chrome-37', customTargets: {}, polyfills: [], overrides: {} }); return { action: 'reset', success: true, message: 'Configuration reset to defaults', newConfig: { defaultBaseline: 'chrome-37', customTargets: {}, polyfills: [], overrides: {} } }; default: throw new Error(`Unknown config action: ${action}`); } } catch (error) { return { action, error: true, message: error.message, suggestion: 'Check the action parameter and required fields. Use action="view" to see available options.' }; } }
• index.js:171-180 (schema)

  Zod input schema defining parameters for the manage_config tool, including action types and optional fields.
  inputSchema: { action: z.enum(["view", "set_baseline", "add_polyfill", "remove_polyfill", "set_override", "add_target", "create_template", "reset"]).optional().default("view").describe("Configuration action to perform"), baseline: z.string().optional().describe("Set default baseline browser target (e.g., 'chrome-37', 'chrome-57')"), polyfill: z.string().optional().describe("Feature name to add/remove from polyfills list"), feature: z.string().optional().describe("Feature name for override setting"), override: z.enum(["supported", "unsupported"]).optional().describe("Force feature support status"), targetName: z.string().optional().describe("Custom target name (e.g., 'chrome-57')"), browser: z.string().optional().describe("Browser name for custom target"), version: z.string().optional().describe("Browser version for custom target") }
• index.js:166-205 (registration)

  Registration of the manage_config tool on the MCP server, including schema and wrapper handler that calls the main handleManageConfig.
  server.registerTool( "manage_config", { title: "Config Manager", description: "Configure browser baselines, polyfills, and feature overrides for more accurate compatibility checking", inputSchema: { action: z.enum(["view", "set_baseline", "add_polyfill", "remove_polyfill", "set_override", "add_target", "create_template", "reset"]).optional().default("view").describe("Configuration action to perform"), baseline: z.string().optional().describe("Set default baseline browser target (e.g., 'chrome-37', 'chrome-57')"), polyfill: z.string().optional().describe("Feature name to add/remove from polyfills list"), feature: z.string().optional().describe("Feature name for override setting"), override: z.enum(["supported", "unsupported"]).optional().describe("Force feature support status"), targetName: z.string().optional().describe("Custom target name (e.g., 'chrome-57')"), browser: z.string().optional().describe("Browser name for custom target"), version: z.string().optional().describe("Browser version for custom target") } }, async (args) => { try { const result = await handleManageConfig(args); return { content: [{ type: "text", text: JSON.stringify(result, null, 2) }] }; } catch (error) { return { content: [{ type: "text", text: JSON.stringify({ error: true, message: error.message, suggestion: "Check the action parameter and required fields. Use action='view' to see available options." }, null, 2) }], isError: true }; } } );
• src/config-manager.js:4-226 (helper)

  ConfigManager class providing persistent configuration storage, loading, updating, and management utilities used by the manage_config handler.
  export class ConfigManager { constructor(projectPath = '.') { this.projectPath = projectPath; this.config = null; this.defaultConfig = { defaultBaseline: 'chrome-37', customTargets: {}, polyfills: [], overrides: {}, browserFallbacks: { chrome: ['37'], // fallback versions if specific version not found firefox: ['78'], safari: ['12'], ie: ['11'], edge: ['18'] } }; } async loadConfig() { if (this.config) return this.config; // Try to load from file first const configPath = path.join(this.projectPath, '.caniuse-config.json'); let fileConfig = {}; try { if (fs.existsSync(configPath)) { const configContent = await fs.promises.readFile(configPath, 'utf8'); fileConfig = JSON.parse(configContent); } } catch (error) { console.warn(`Warning: Could not load config from ${configPath}: ${error.message}`); } // Merge with environment variables const envConfig = this._loadFromEnvironment(); // Merge all configurations: default < file < environment this.config = { ...this.defaultConfig, ...fileConfig, ...envConfig, // Merge nested objects properly customTargets: { ...this.defaultConfig.customTargets, ...fileConfig.customTargets, ...envConfig.customTargets }, polyfills: [ ...this.defaultConfig.polyfills, ...(fileConfig.polyfills || []), ...(envConfig.polyfills || []) ], overrides: { ...this.defaultConfig.overrides, ...fileConfig.overrides, ...envConfig.overrides }, browserFallbacks: { ...this.defaultConfig.browserFallbacks, ...fileConfig.browserFallbacks, ...envConfig.browserFallbacks } }; return this.config; } _loadFromEnvironment() { const envConfig = {}; if (process.env.CANIUSE_DEFAULT_BASELINE) { envConfig.defaultBaseline = process.env.CANIUSE_DEFAULT_BASELINE; } if (process.env.CANIUSE_POLYFILLS) { try { envConfig.polyfills = JSON.parse(process.env.CANIUSE_POLYFILLS); } catch (error) { envConfig.polyfills = process.env.CANIUSE_POLYFILLS.split(',').map(p => p.trim()); } } if (process.env.CANIUSE_OVERRIDES) { try { envConfig.overrides = JSON.parse(process.env.CANIUSE_OVERRIDES); } catch (error) { console.warn('Invalid CANIUSE_OVERRIDES environment variable format'); } } return envConfig; } async getBrowserTargets() { const config = await this.loadConfig(); // Built-in targets const builtInTargets = { 'chrome-37': { browser: 'chrome', version: '37' }, 'chrome-latest': { browser: 'chrome', version: 'latest' }, 'firefox-esr': { browser: 'firefox', version: '78' }, 'safari-12': { browser: 'safari', version: '12' }, 'ie-11': { browser: 'ie', version: '11' }, 'edge-legacy': { browser: 'edge', version: '18' } }; // Merge with custom targets return { ...builtInTargets, ...config.customTargets }; } async resolveTargetVersion(targetString) { const config = await this.loadConfig(); const targets = await this.getBrowserTargets(); // Check if it's a known target if (targets[targetString]) { return targets[targetString]; } // Try to parse browser-version format (e.g., "chrome-57") const match = targetString.match(/^([a-z]+)-(.+)$/); if (match) { const [, browser, version] = match; return { browser, version }; } // Fallback to default baseline const defaultTarget = targets[config.defaultBaseline]; if (defaultTarget) { return defaultTarget; } // Final fallback return { browser: 'chrome', version: '37' }; } async isFeaturePolyfilled(featureName) { const config = await this.loadConfig(); return config.polyfills.includes(featureName); } async getFeatureOverride(featureName) { const config = await this.loadConfig(); return config.overrides[featureName]; } async getFallbackVersions(browser) { const config = await this.loadConfig(); return config.browserFallbacks[browser] || []; } async updateConfig(updates) { const config = await this.loadConfig(); const newConfig = { ...config, ...updates }; const configPath = path.join(this.projectPath, '.caniuse-config.json'); await fs.promises.writeFile(configPath, JSON.stringify(newConfig, null, 2)); // Reload config this.config = null; return await this.loadConfig(); } async addPolyfill(featureName) { const config = await this.loadConfig(); if (!config.polyfills.includes(featureName)) { config.polyfills.push(featureName); await this.updateConfig({ polyfills: config.polyfills }); } } async removePolyfill(featureName) { const config = await this.loadConfig(); const index = config.polyfills.indexOf(featureName); if (index > -1) { config.polyfills.splice(index, 1); await this.updateConfig({ polyfills: config.polyfills }); } } async setFeatureOverride(featureName, supportStatus) { const config = await this.loadConfig(); config.overrides[featureName] = supportStatus; await this.updateConfig({ overrides: config.overrides }); } // Helper to create a config file template static async createConfigTemplate(projectPath) { const configPath = path.join(projectPath, '.caniuse-config.json'); const template = { "$schema": "https://json-schema.org/draft-07/schema#", "$comment": "CanIUse MCP Configuration", "defaultBaseline": "chrome-37", "customTargets": { "chrome-57": { "browser": "chrome", "version": "57" }, "chrome-60": { "browser": "chrome", "version": "60" } }, "polyfills": [ "css-grid", "flexbox", "promises" ], "overrides": { "css-variables": "supported" }, "browserFallbacks": { "chrome": ["37", "40", "45"], "firefox": ["78", "68"], "safari": ["12", "11"], "ie": ["11"], "edge": ["18", "16"] } }; await fs.promises.writeFile(configPath, JSON.stringify(template, null, 2)); return configPath; } }