diff --git a/packages/rececss-core/src/2_usecases/BuildRulesets/BuildRulesets.interface.ts b/packages/rececss-core/src/2_usecases/BuildRulesets/BuildRulesets.interface.ts
index 159cab9..e8495a2 100644
--- a/packages/rececss-core/src/2_usecases/BuildRulesets/BuildRulesets.interface.ts
+++ b/packages/rececss-core/src/2_usecases/BuildRulesets/BuildRulesets.interface.ts
@@ -1,3 +1,4 @@
+import { IRuleset } from "src/1_entities/Ruleset";
 import RulesetsListBuilder, {
   IRulesetsListBuilder,
 } from "../../1_entities/RulesetsListBuilder";
@@ -6,6 +7,7 @@ export interface Props extends IRulesetsListBuilder.DTO {}
 
 export interface DTO {
   values: ValuesMap;
+  definitions: IRuleset.DTO[];
 }
 
 export type ClassnamesMap = IRulesetsListBuilder.ClassnamesMap;
diff --git a/packages/rececss-core/src/2_usecases/BuildRulesets/BuildRulesets.test.ts b/packages/rececss-core/src/2_usecases/BuildRulesets/BuildRulesets.test.ts
index 22c3cf3..71dfef9 100644
--- a/packages/rececss-core/src/2_usecases/BuildRulesets/BuildRulesets.test.ts
+++ b/packages/rececss-core/src/2_usecases/BuildRulesets/BuildRulesets.test.ts
@@ -7,6 +7,8 @@ const toString = (rs: IRuleset.DTO[]) =>
 const basic: IBuildRulesets.Props = {
   variantsMap: {},
   classnamesMap: {
+    width: "w-$0",
+
     filter: "ftr_$0",
     filterCompound: "ftr~",
     filterBlur: "~bl_$0",
@@ -50,6 +52,8 @@ const basic: IBuildRulesets.Props = {
     transformPerspective: "~prs_$0",
   },
   declarationsMap: {
+    width: "width: $0;",
+
     filter: "filter: $0;",
     filterCompound:
       "filter: blur(var(--filterBlur)) brightness(var(--filterBrightness)) contrast(var(--filterContrast)) drop-shadow(var(--filterDropShadow)) grayscale(var(--filterGrayscale)) hue-rotate(var(--filterHueRotate)) invert(var(--filterInvert)) opacity(var(--filterOpacity)) saturate(var(--filterSaturate)) sepia(var(--filterSepia));",
@@ -122,13 +126,27 @@ const withVariants: IBuildRulesets.Props = {
 describe("BuildRulesets usecase", () => {
   it("should not crash if nothing is provided", () => {
     const build = BuildRulesets.create(basic);
-    const res = build.exec({ values: {} });
+    const res = build.exec({ values: {}, definitions: [] });
     expect(res).toEqual([]);
   });
 
+  it("should build from values and definitions", () => {
+    const build = BuildRulesets.create(basic);
+    const res = build.exec({
+      values: { width: { "20": "20px" } },
+      definitions: [{ classname: "height-sm", declarations: "height: 12px;" }],
+    });
+
+    expect(toString(res)).toEqual([
+      ".w-20 { width: 20px; }",
+      ".height-sm { height: 12px; }",
+    ]);
+  });
+
   it("should build font size rulesets", () => {
     const build = BuildRulesets.create(basic);
     const res = build.exec({
+      definitions: [],
       values: {
         fontSize: { "20": "20px", "2em": "2em", md: "16px/24px" },
       },
@@ -144,6 +162,7 @@ describe("BuildRulesets usecase", () => {
   it("should build flex grid rulesets", () => {
     const build = BuildRulesets.create(basic);
     const res = build.exec({
+      definitions: [],
       values: {
         flexGrid: { cols: 6 },
       },
@@ -164,6 +183,7 @@ describe("BuildRulesets usecase", () => {
   it("should build flex grid rulesets with gutters", () => {
     const build = BuildRulesets.create(basic);
     const res = build.exec({
+      definitions: [],
       values: {
         flexGrid: {
           cols: 12,
@@ -172,6 +192,7 @@ describe("BuildRulesets usecase", () => {
         },
       },
     });
+
     // prettier-ignore
     expect(toString(res)).toEqual([
       ".fxrow { display: flex; margin-left: -5px; margin-right: -5px; }",
@@ -200,6 +221,7 @@ describe("BuildRulesets usecase", () => {
     const build = BuildRulesets.create(basic);
 
     const res = build.exec({
+      definitions: [],
       values: {
         transform: {
           custom: "translate(120px, 50%)",
@@ -260,6 +282,7 @@ describe("BuildRulesets usecase", () => {
     const build = BuildRulesets.create(basic);
 
     const res = build.exec({
+      definitions: [],
       values: {
         filterCompound: {},
         filter: {
diff --git a/packages/rececss-core/src/2_usecases/BuildRulesets/BuildRulesets.ts b/packages/rececss-core/src/2_usecases/BuildRulesets/BuildRulesets.ts
index d56d3b8..10fd89c 100644
--- a/packages/rececss-core/src/2_usecases/BuildRulesets/BuildRulesets.ts
+++ b/packages/rececss-core/src/2_usecases/BuildRulesets/BuildRulesets.ts
@@ -36,6 +36,10 @@ export default class BuildRulesets {
       );
     });
 
+    dto.definitions.forEach((dto) => {
+      this.builder.addRulesetFromDTO(dto);
+    });
+
     return this.builder.getResult();
   }
 }
diff --git a/packages/rececss-core/src/3_adapters/StylesheetsController/StylesheetsController.ts b/packages/rececss-core/src/3_adapters/StylesheetsController/StylesheetsController.ts
index 88c037d..a0848ba 100644
--- a/packages/rececss-core/src/3_adapters/StylesheetsController/StylesheetsController.ts
+++ b/packages/rececss-core/src/3_adapters/StylesheetsController/StylesheetsController.ts
@@ -16,6 +16,7 @@ export default class StylesheetsController {
     const rulesetsProps = this.io.getRulesetsBuildProps();
     const rulesets = BuildRulesets.create(rulesetsProps).exec({
       values: this.io.getRulesetsValues(),
+      definitions: this.io.getRulesetsDefinitions(),
     });
 
     const assetsProps = this.io.getAssetsGenerationProps();
diff --git a/packages/rececss-core/src/3_adapters/interfaces.ts b/packages/rececss-core/src/3_adapters/interfaces.ts
index 4f6c991..9b74e5d 100644
--- a/packages/rececss-core/src/3_adapters/interfaces.ts
+++ b/packages/rececss-core/src/3_adapters/interfaces.ts
@@ -1,3 +1,4 @@
+import { IRuleset } from "src/1_entities/Ruleset";
 import { IGenerateStylesheetAssets } from "../2_usecases/GenerateStylesheetAssets";
 import { IBuildRulesets } from "../2_usecases/BuildRulesets";
 
@@ -5,6 +6,7 @@ export interface IInputOutput {
   getAssetsGenerationProps(): IGenerateStylesheetAssets.Props;
   getRulesetsBuildProps(): IBuildRulesets.Props;
   getRulesetsValues(): IBuildRulesets.DTO["values"];
+  getRulesetsDefinitions(): IRuleset.DTO[];
   getMediaQueries: () => Record<string, string>;
   outputAssets(assets: { name: string; contents: string }[]): Promise<void>;
 }
diff --git a/packages/rececss-core/src/4_infrastructures/config/Config.interfaces.ts b/packages/rececss-core/src/4_infrastructures/config/Config.interfaces.ts
index f7a69bf..38b10de 100644
--- a/packages/rececss-core/src/4_infrastructures/config/Config.interfaces.ts
+++ b/packages/rececss-core/src/4_infrastructures/config/Config.interfaces.ts
@@ -1,3 +1,4 @@
+import { IRuleset } from "../../1_entities/Ruleset";
 import { IBuildRulesets } from "../../2_usecases/BuildRulesets";
 
 export interface Props {
@@ -35,6 +36,7 @@ export interface DTO {
   values: CreatorFn<RawValues> | RawValues;
   variants?: CreatorFn<Variants> | Variants;
   associations?: CreatorFn<Associations> | Associations;
+  definitions?: IRuleset.DTO[];
 }
 
 type ValueOf<T> = T[keyof T];
diff --git a/packages/rececss-core/src/4_infrastructures/config/Config.test.ts b/packages/rececss-core/src/4_infrastructures/config/Config.test.ts
index 4d457f0..ab67754 100644
--- a/packages/rececss-core/src/4_infrastructures/config/Config.test.ts
+++ b/packages/rececss-core/src/4_infrastructures/config/Config.test.ts
@@ -84,6 +84,16 @@ describe("Config", () => {
     expect(config.getVariantSeparator()).toBe(":");
   });
 
+  test("definitions getter", () => {
+    const config = configBasic.create(dto);
+    expect(config.getRulesetDefinitions()).toEqual([
+      {
+        classname: "width-20px",
+        declarations: "width: 20px;",
+      },
+    ]);
+  });
+
   test("classnames getter", () => {
     const classesConfig = configBasic.create({
       output: { path: "" },
diff --git a/packages/rececss-core/src/4_infrastructures/config/Config.ts b/packages/rececss-core/src/4_infrastructures/config/Config.ts
index 4d08930..51910e6 100644
--- a/packages/rececss-core/src/4_infrastructures/config/Config.ts
+++ b/packages/rececss-core/src/4_infrastructures/config/Config.ts
@@ -115,6 +115,10 @@ export default class Config {
     return result;
   }
 
+  getRulesetDefinitions() {
+    return this.dto.definitions || [];
+  }
+
   private parseRuleValue(rule?: any): Record<string, string> {
     if (!rule) return {};
     return Object.keys(rule).reduce((acc, key) => {
diff --git a/packages/rececss-core/src/4_infrastructures/io/ConfigFileSystemIO.test.ts b/packages/rececss-core/src/4_infrastructures/io/ConfigFileSystemIO.test.ts
index 1333794..f855707 100644
--- a/packages/rececss-core/src/4_infrastructures/io/ConfigFileSystemIO.test.ts
+++ b/packages/rececss-core/src/4_infrastructures/io/ConfigFileSystemIO.test.ts
@@ -1,27 +1,9 @@
 import path from "path";
 import IO from "./ConfigFileSystemIO";
 
+const configDto = require("../../../tests/__fixtures__/rececss.config");
 const writeFiles = jest.fn(() => Promise.resolve());
 
-const configDto = {
-  output: {
-    path: "./website/styles",
-    filename: "rececss",
-    extension: "css",
-    splitByMedia: false,
-    purge: { content: ["./website/pages/**/*.js"] },
-  },
-  media: {
-    md: "only screen and (min-width: 768px)",
-    lg: "only screen and (min-width: 1024px)",
-  },
-  separator: {
-    media: ":",
-    variant: ":",
-  },
-  values: {},
-};
-
 describe("ConfigFileSystemIO", () => {
   it("should return media queries", () => {
     const io = IO.create(configDto, writeFiles);
@@ -42,13 +24,21 @@ describe("ConfigFileSystemIO", () => {
     });
   });
 
+  it("should return ruleset definitions", () => {
+    const io = IO.create(configDto, writeFiles);
+    const defs = io.getRulesetsDefinitions();
+    expect(defs).toEqual([
+      { classname: "width-20px", declarations: "width: 20px;" },
+    ]);
+  });
+
   it("should return css processor input", () => {
     const io = IO.create(configDto, writeFiles);
     const input = io.getCSSProccesorInput();
     expect(input).toEqual({ content: ["./website/pages/**/*.js"] });
   });
 
-  it("should output assets by calling fs.writeFiles with proper filepaths", async () => {
+  it("should output assets by calling fs.writeFiles with proper filepaths", () => {
     const io = IO.create(configDto, writeFiles);
     io.outputAssets([{ name: "some", contents: "contents" }]);
     expect(writeFiles).toHaveBeenCalledWith([
diff --git a/packages/rececss-core/src/4_infrastructures/io/ConfigFileSystemIO.ts b/packages/rececss-core/src/4_infrastructures/io/ConfigFileSystemIO.ts
index 5955dad..ba5a620 100644
--- a/packages/rececss-core/src/4_infrastructures/io/ConfigFileSystemIO.ts
+++ b/packages/rececss-core/src/4_infrastructures/io/ConfigFileSystemIO.ts
@@ -23,6 +23,10 @@ export default class ConfigFileSystemIO implements IInputOutput {
     return this.config.getRulesetsValues();
   }
 
+  getRulesetsDefinitions() {
+    return this.config.getRulesetDefinitions();
+  }
+
   getRulesetsBuildProps() {
     return {
       classnamesMap: this.config.getRulesetsClassnames(),
diff --git a/packages/rececss-core/tests/__fixtures__/rececss.config.js b/packages/rececss-core/tests/__fixtures__/rececss.config.js
index c1f52de..2452f93 100644
--- a/packages/rececss-core/tests/__fixtures__/rececss.config.js
+++ b/packages/rececss-core/tests/__fixtures__/rececss.config.js
@@ -15,4 +15,10 @@ module.exports = {
     variant: ":",
   },
   values: {},
+  definitions: [
+    {
+      classname: "width-20px",
+      declarations: "width: 20px;",
+    },
+  ],
 };
diff --git a/packages/rececss-core/tests/__mocks__/io.ts b/packages/rececss-core/tests/__mocks__/io.ts
index f9574c9..f382ee6 100644
--- a/packages/rececss-core/tests/__mocks__/io.ts
+++ b/packages/rececss-core/tests/__mocks__/io.ts
@@ -6,6 +6,7 @@ const ioMock: IInputOutput = {
   outputAssets: jest.fn(),
   getRulesetsBuildProps: jest.fn(),
   getRulesetsValues: jest.fn(() => ({})),
+  getRulesetsDefinitions: jest.fn(() => []),
 };
 
 export default ioMock;