# Using Checkly CLI Constructs - Checkly Docs > Build monitoring infrastructure using JavaScript/TypeScript and the Checkly CLI Source: https://www.checklyhq.com/docs/constructs/overview/ --- - Project Structure - Project Configuration Global Configuration - Local Configuration - Logical IDs - Programming with Constructs Getting Started # Using Checkly CLI Constructs Build monitoring infrastructure using JavaScript/TypeScript and the Checkly CLI Every resource you create using the [Checkly CLI](https://www.checklyhq.com/docs/cli/overview) is represented by a “construct”: it’s a class you import from `checkly/constructs`, for instance an `ApiCheck` or `EmailAlertChannel`. A construct is the “as-code” representation of the eventual resource created / deleted / updated on the Checkly cloud once you run `npx checkly deploy`. You must install the [Checkly CLI](https://www.checklyhq.com/docs/cli/overview) before you can use constructs. Constructs are JavaScript/TypeScript classes that represent your all monitoring resources. Import them from `checkly/constructs` to create checks, alert channels, and other resources in code. api.check.ts ``` import { ApiCheck, AssertionBuilder } from 'checkly/constructs' new ApiCheck('api-health-check', { name: 'API Health Check', request: { url: 'https://danube-web.shop/api/books', method: 'GET', assertions: [ AssertionBuilder.statusCode().equals(200), ], }, }) ``` ``` const { ApiCheck, AssertionBuilder } = require('checkly/constructs') new ApiCheck('api-health-check', { name: 'API Health Check', request: { url: 'https://danube-web.shop/api/books', method: 'GET', assertions: [ AssertionBuilder.statusCode().equals(200), ], }, }) ``` The Checkly CLI supports JavaScript and TypeScript. The documentation focuses on TypeScript, because we recommend using TypeScript for a better developer experience. Test this API check with `npx checkly test` and transform it to production monitoring with `npx checkly deploy`. ## ​ Project Structure - `checkly.config.ts` - Mandatory global project and CLI configuration. We recommend using TypeScript. - `src/__checks__/*` - TS/JS files defining your checks and other resources. - `package.json` - Standard NPM project manifest. Here is an example directory tree of what that would look like: ``` . |-- checkly.config.ts |-- package.json `-- src `-- __checks__ |-- alert-channels.ts |-- api-check.check.ts `-- homepage.spec.ts ``` The `checkly.config.ts` at the root of your project defines a range of defaults for all your checks. ## ​ Project Configuration As your project grows, you will want to override these defaults for specific checks or check groups. The recommended way to tackle this is using a mix of **global** and **local** configuration. ### ​ Global Configuration As mentioned, your global `checkly.config.ts` holds a set of defaults for your project, checks, and some CLI commands. Use `defineConfig` to configure your Checkly project. checkly.config.ts ``` import { defineConfig } from "checkly" import { Frequency } from "checkly/constructs" export default defineConfig({ projectName: "Website Monitoring", logicalId: "website-monitoring-1", repoUrl: "https://github.com/you/your-project", checks: { activated: true, muted: false, runtimeId: "2025.04", frequency: Frequency.EVERY_5M, locations: ["us-east-1", "eu-west-1"], tags: ["website", "api"], checkMatch: "**/*.check.ts", browserChecks: { frequency: Frequency.EVERY_10M, testMatch: "browsers/**/*.spec.ts", }, multiStepChecks: { testMatch: "multistep/**/*.spec.ts", }, }, cli: { runLocation: "eu-west-1", }, }) ``` ``` const { defineConfig } = require("checkly") const { Frequency } = require("checkly/constructs") module.exports = defineConfig({ projectName: "Website Monitoring", logicalId: "website-monitoring-1", repoUrl: "https://github.com/you/your-project", checks: { activated: true, muted: false, runtimeId: "2025.04", frequency: Frequency.EVERY_5M, locations: ["us-east-1", "eu-west-1"], tags: ["website", "api"], checkMatch: "**/*.check.js", browserChecks: { frequency: Frequency.EVERY_10M, testMatch: "browsers/**/*.spec.js", }, multiStepChecks: { testMatch: "multistep/**/*.spec.js", }, }, cli: { runLocation: "eu-west-1", }, }) ``` Find a full reference of all project properties in [the `Project` construct section](https://www.checklyhq.com/docs/constructs/project). ### ​ Local Configuration Override any of the `checks` global configuration settings at the individual check level. __checks__/api.check.ts ``` import { ApiCheck, AssertionBuilder, Frequency } from 'checkly/constructs' new ApiCheck('books-api', { name: 'Books API', locations: ['ap-south-1'], // overrides the locations property frequency: Frequency.EVERY_30M, // overrides the frequency property request: { method: 'GET', url: 'https://danube-web.shop/api/books', assertions: [AssertionBuilder.statusCode().equals(200)], }, }) ``` ``` const { ApiCheck, AssertionBuilder, Frequency } = require('checkly/constructs') new ApiCheck('books-api', { name: 'Books API', locations: ['ap-south-1'], // overrides the locations property frequency: Frequency.EVERY_30M, // overrides the frequency property request: { method: 'GET', url: 'https://danube-web.shop/api/books', assertions: [AssertionBuilder.statusCode().equals(200)], }, }) ``` Find a full reference of all check properties in [the `ApiCheck` construct](https://www.checklyhq.com/docs/constructs/api-check) or [`BrowserCheck` construct section](https://www.checklyhq.com/docs/constructs/browser-check). ## ​ Logical IDs Assigning a `logicalId` is crucial when creating a construct. Remember the following rules when creating and updating constructs: - Every construct needs to have a `logicalId`. This is the first argument when instantiating a class, i.e. ``` const check = new ApiCheck('my-logical-id', { name: 'My API check' }) ``` - Every `logicalId` needs to be unique within the scope of a `Project`. - A `Project` also has a `logicalId`. This needs to be unique within the scope of the Checkly account. - A `logicalId` can be any string up to 255 characters in length. - There is no hard limit on the amount of `Project`s you can have in your Checkly account. Behind the scenes, we use the `logicalId` to create a graph of your resources so we know what to persist, update and remove from our database. Changing the `logicalId` on an existing resource in your code base will tell the Checkly backend that a resource was removed and a new resource was created. When using the Checkly CLI to manage multiple projects and repositories, each project’s `logicalId` should be unique within the Checkly account. The project’s `logicalId` is used during the Checkly CLI commands to detect exactly which project is being used. If multiple projects are using the same project `logicalId`, deploying one project will delete the checks that were deployed by another project. The project `logicalId` can be configured in the project’s [global configuration](https://www.checklyhq.com/docs/constructs/project). When changing the logical ID of a project you will keep all resources on your Checkly account, unless you run [`npx checkly destroy`](https://www.checklyhq.com/docs/cli/checkly-destroy) to remove the old project. ## ​ Programming with Constructs All resources you can create and manage using the Checkly CLI are derived from “constructs”. These constructs are just [TypeScript classes](https://github.com/checkly/checkly-cli/tree/main/packages/cli/src/constructs). You can use standard JS/TS programming to use these constructs to create the monitoring setup of your choice. Loops, variables, if-statements, file imports, extensions etc. [Here are some examples.](https://www.checklyhq.com/docs/constructs/dynamic-monitor-creation) Was this page helpful? [Suggest edits](https://github.com/checkly/docs/edit/main/constructs/overview.mdx)[Raise issue](https://github.com/checkly/docs/issues/new?title=Issue%20on%20docs&body=Path:%20/constructs/overview) [Create Checks Automatically from Files Next](https://www.checklyhq.com/docs/constructs/including-checks) [x](https://x.com/checklyhq)[github](https://github.com/checkly)[linkedin](https://linkedin.com/company/checkly) [Powered by This documentation is built and hosted on Mintlify, a developer documentation platform](https://www.mintlify.com/?utm_campaign=poweredBy&utm_medium=referral&utm_source=checkly-422f444a)