Adding A Feature

Adding a New Tool to @webiny/stdlib

This mirrors the "Step-by-step: Adding a New Tool to an Existing Package" section in the repo's AGENTS.md, which is the authoritative source — check there if this drifts.

First decide which slice the tool belongs in, based on its runtime dependencies:

| Uses only JS built-ins / standard lib | → @webiny/stdlib root (src/) | | Uses node:* APIs or Node-only npm packages | → @webiny/stdlib/node (src/node/) | | Uses window, document, React, browser APIs | → @webiny/stdlib/browser (src/browser/) |

src/node/ and src/browser/ must NOT import from each other. Both may import common code via ~/common/index.js.

Example below: adding HttpTool to @webiny/stdlib/node. Substitute the appropriate slice and path for your tool.

Steps

1. Create the abstraction at src/node/features/HttpTool/abstractions/HttpTool.ts:

   • Define interface IHttpTool with JSDoc on each method.
   • Export const HttpTool = createAbstraction<IHttpTool>("Core/HttpTool").
   • Export namespace HttpTool { export type Interface = IHttpTool }.

2. Create the abstraction barrel at src/node/features/HttpTool/abstractions/index.ts:

   • export { HttpTool } from "./HttpTool.js";

3. Create the implementation at src/node/features/HttpTool/HttpTool.ts:

   • Rename the token import to avoid a name clash: import { HttpTool as HttpToolAbstraction } from "./abstractions/HttpTool.js";
   • Import cross-slice dependencies via the common barrel: import { Logger } from "~/common/index.js";
   • class HttpToolImpl implements HttpToolAbstraction.Interface { ... }
   • export const HttpTool = HttpToolAbstraction.createImplementation({ implementation: HttpToolImpl, dependencies: [...] })
   • The dependencies array order must match the constructor parameter order exactly.

4. Create the feature at src/node/features/HttpTool/feature.ts:

   • export const HttpToolFeature = createFeature({ name: "Core/HttpToolFeature", register(container) { container.register(HttpTool).inSingletonScope(); } })

5. Create the feature index at src/node/features/HttpTool/index.ts:

   • export { HttpTool } from "./abstractions/index.js";
   • export { HttpToolFeature } from "./feature.js";
   • Never re-export the implementation class or the createImplementation output.

6. Create the feature README at src/node/features/HttpTool/README.md:

   • One-paragraph description — what it does and when to reach for it.
   • Interface section — the public methods with JSDoc (copy from the abstraction file).
   • Usage section — two code snippets: DI container wiring, and a createXxx() factory function.
   • Prepend YAML front-matter (name, description, context) so the README is discoverable by the MCP server — see the front-matter block at the top of any existing feature README for the exact shape.
   • Update the repo root README.md table to add a row pointing to the new feature README.

7. Add to the slice barrel src/node/index.ts:

   • export { HttpTool, HttpToolFeature } from "./features/HttpTool/index.js";

8. Write tests at __tests__/node/HttpTool.test.ts:

   • Create a makeContainer() helper — see the testing-patterns skill.
   • Cover the happy path and error paths.
   • Node tests do not need a // @vitest-environment directive (only browser tests do).

9. Run the pre-commit chain until fully clean:

   yarn && yarn adio && yarn format:fix && yarn lint:fix && yarn typecheck && yarn build && yarn test:coverage
   

   All steps must pass with zero errors and zero warnings before staging and committing. If any step fails, fix the issue and run the full chain again from the start.

Conventions to keep in mind throughout

• No default exports. Always use named exports.
• JSDoc comments are preferred on interface methods, abstraction types, and public class methods — they're read by both IDE tooling and agents. Don't write comments that just restate the method name.
• Strict TypeScript — all strict flags in tsconfig.json must pass.
• .js extensions in package source imports — under src/, import { Foo } from "./Foo.js" (not .ts); tsgo resolves .js to .ts at compile time. (Exception: scripts/, which runs directly under Node 24 and needs real .ts extensions.)
• node: prefix for Node built-ins — import { readFileSync } from "node:fs", never "fs".
• Singletons via DI — register utils as .inSingletonScope() unless there's a reason not to.
• DI token names use "Domain/ToolName" format — "Core/" prefix for common utils, "Node/" prefix for Node-specific ones.
• Namespace pattern for interface types — always export namespace ToolName { export type Interface = IToolName } alongside the token.

See the di-patterns skill for the underlying abstraction/implementation/feature mechanics, and AGENTS.md's "Step-by-step: Adding a New Slice to @webiny/stdlib" section if you're adding an entirely new runtime environment rather than a tool within an existing one.