diff --git a/maxun-core/browserSide/scraper.js b/maxun-core/browserSide/scraper.js
new file mode 100644
index 00000000..c411f642
--- /dev/null
+++ b/maxun-core/browserSide/scraper.js
@@ -0,0 +1,226 @@
+/* eslint-disable @typescript-eslint/no-unused-vars */
+
+const area = (element) => element.offsetHeight * element.offsetWidth;
+
+function getBiggestElement(selector) {
+  const elements = Array.from(document.querySelectorAll(selector));
+  const biggest = elements.reduce(
+    (max, elem) => (
+      area(elem) > area(max) ? elem : max),
+    { offsetHeight: 0, offsetWidth: 0 },
+  );
+  return biggest;
+}
+
+/**
+ * Generates structural selector (describing element by its DOM tree location).
+ *
+ * **The generated selector is not guaranteed to be unique!** (In fact, this is
+ *    the desired behaviour in here.)
+ * @param {HTMLElement} element Element being described.
+ * @returns {string} CSS-compliant selector describing the element's location in the DOM tree.
+ */
+function GetSelectorStructural(element) {
+  // Base conditions for the recursive approach.
+  if (element.tagName === 'BODY') {
+    return 'BODY';
+  }
+  const selector = element.tagName;
+  if (element.parentElement) {
+    return `${GetSelectorStructural(element.parentElement)} > ${selector}`;
+  }
+
+  return selector;
+}
+
+/**
+ * Heuristic method to find collections of "interesting" items on the page.
+ * @returns {Array<HTMLElement>} A collection of interesting DOM nodes
+ *  (online store products, plane tickets, list items... and many more?)
+ */
+function scrapableHeuristics(maxCountPerPage = 50, minArea = 20000, scrolls = 3, metricType = 'size_deviation') {
+  const restoreScroll = (() => {
+    const { scrollX, scrollY } = window;
+    return () => {
+      window.scrollTo(scrollX, scrollY);
+    };
+  })();
+
+  /**
+* @typedef {Array<{x: number, y: number}>} Grid
+*/
+
+  /**
+ * Returns an array of grid-aligned {x,y} points.
+ * @param {number} [granularity=0.005] sets the number of generated points
+ *  (the higher the granularity, the more points).
+ * @returns {Grid} Array of {x, y} objects.
+ */
+  function getGrid(startX = 0, startY = 0, granularity = 0.005) {
+    const width = window.innerWidth;
+    const height = window.innerHeight;
+
+    const out = [];
+    for (let x = 0; x < width; x += 1 / granularity) {
+      for (let y = 0; y < height; y += 1 / granularity) {
+        out.push({ x: startX + x, y: startY + y });
+      }
+    }
+    return out;
+  }
+
+  let maxSelector = { selector: 'body', metric: 0 };
+
+  const updateMaximumWithPoint = (point) => {
+    const currentElement = document.elementFromPoint(point.x, point.y);
+    const selector = GetSelectorStructural(currentElement);
+
+    const elements = Array.from(document.querySelectorAll(selector))
+      .filter((element) => area(element) > minArea);
+
+    // If the current selector targets less than three elements,
+    // we consider it not interesting (would be a very underwhelming scraper)
+    if (elements.length < 3) {
+      return;
+    }
+
+    let metric = null;
+
+    if (metricType === 'total_area') {
+      metric = elements
+        .reduce((p, x) => p + area(x), 0);
+    } else if (metricType === 'size_deviation') {
+      // This could use a proper "statistics" approach... but meh, so far so good!
+      const sizes = elements
+        .map((element) => area(element));
+
+      metric = (1 - (Math.max(...sizes) - Math.min(...sizes)) / Math.max(...sizes));
+    }
+
+    // console.debug(`Total ${metricType} is ${metric}.`)
+    if (metric > maxSelector.metric && elements.length < maxCountPerPage) {
+      maxSelector = { selector, metric };
+    }
+  };
+
+  for (let scroll = 0; scroll < scrolls; scroll += 1) {
+    window.scrollTo(0, scroll * window.innerHeight);
+
+    const grid = getGrid();
+
+    grid.forEach(updateMaximumWithPoint);
+  }
+
+  restoreScroll();
+
+  let out = Array.from(document.querySelectorAll(maxSelector.selector));
+
+  const different = (x, i, a) => a.findIndex((e) => e === x) === i;
+  // as long as we don't merge any two elements by substituing them for their parents,
+  // we substitute.
+  while (out.map((x) => x.parentElement).every(different)
+    && out.forEach((x) => x.parentElement !== null)) {
+    out = out.map((x) => x.parentElement ?? x);
+  }
+
+  return out;
+}
+
+/**
+ * Returns a "scrape" result from the current page.
+ * @returns {Array<Object>} *Curated* array of scraped information (with sparse rows removed)
+ */
+function scrape(selector = null) {
+  /**
+   * **crudeRecords** contains uncurated rundowns of "scrapable" elements
+   * @type {Array<Object>}
+   */
+  const crudeRecords = (selector
+    ? Array.from(document.querySelectorAll(selector))
+    : scrapableHeuristics())
+    .map((record) => ({
+      ...Array.from(record.querySelectorAll('img'))
+        .reduce((p, x, i) => {
+          let url = null;
+          if (x.srcset) {
+            const urls = x.srcset.split(', ');
+            [url] = urls[urls.length - 1].split(' ');
+          }
+
+          /**
+             * Contains the largest elements from `srcset` - if `srcset` is not present, contains
+             * URL from the `src` attribute
+             *
+             * If the `src` attribute contains a data url, imgUrl contains `undefined`.
+             */
+          let imgUrl;
+          if (x.srcset) {
+            imgUrl = url;
+          } else if (x.src.indexOf('data:') === -1) {
+            imgUrl = x.src;
+          }
+
+          return ({
+            ...p,
+            ...(imgUrl ? { [`img_${i}`]: imgUrl } : {}),
+          });
+        }, {}),
+      ...record.innerText.split('\n')
+        .reduce((p, x, i) => ({
+          ...p,
+          [`record_${String(i).padStart(4, '0')}`]: x.trim(),
+        }), {}),
+    }));
+
+  return crudeRecords;
+}
+
+/**
+ * Given an object with named lists of elements,
+ *  groups the elements by their distance in the DOM tree.
+ * @param {Object.<string, object[]>} lists The named lists of HTML elements.
+ * @returns {Array.<Object.<string, string>>}
+ */
+function scrapeSchema(lists) {
+  function omap(object, f, kf = (x) => x) {
+    return Object.fromEntries(
+      Object.entries(object)
+        .map(([k, v]) => [kf(k), f(v)]),
+    );
+  }
+
+  function ofilter(object, f) {
+    return Object.fromEntries(
+      Object.entries(object)
+        .filter(([k, v]) => f(k, v)),
+    );
+  }
+
+  function getSeedKey(listObj) {
+    const maxLength = Math.max(...Object.values(omap(listObj, (x) => x.length)));
+    return Object.keys(ofilter(listObj, (_, v) => v.length === maxLength))[0];
+  }
+
+  function getMBEs(elements) {
+    return elements.map((element) => {
+      let candidate = element;
+      const isUniqueChild = (e) => elements
+        .filter((elem) => e.parentNode?.contains(elem))
+        .length === 1;
+
+      while (candidate && isUniqueChild(candidate)) {
+        candidate = candidate.parentNode;
+      }
+
+      return candidate;
+    });
+  }
+
+  const seedName = getSeedKey(lists);
+  const MBEs = getMBEs(lists[seedName]);
+
+  return MBEs.map((mbe) => omap(
+    lists,
+    (listOfElements) => listOfElements.find((elem) => mbe.contains(elem))?.innerText,
+  ));
+}
\ No newline at end of file
diff --git a/maxun-core/index.ts b/maxun-core/index.ts
new file mode 100644
index 00000000..571f5781
--- /dev/null
+++ b/maxun-core/index.ts
@@ -0,0 +1,8 @@
+import Interpreter from './interpret';
+
+export default Interpreter;
+export { default as Preprocessor } from './preprocessor';
+export type {
+  WorkflowFile, WhereWhatPair, Where, What,
+} from './types/workflow';
+export { unaryOperators, naryOperators, meta as metaOperators } from './types/logic';
\ No newline at end of file
diff --git a/maxun-core/interpret.ts b/maxun-core/interpret.ts
new file mode 100644
index 00000000..9ac32b0e
--- /dev/null
+++ b/maxun-core/interpret.ts
@@ -0,0 +1,459 @@
+/* eslint-disable no-await-in-loop, no-restricted-syntax */
+import { Page, PageScreenshotOptions } from 'playwright';
+import path from 'path';
+
+import { EventEmitter } from 'events';
+import {
+  Where, What, PageState, Workflow, WorkflowFile,
+  ParamType, SelectorArray, CustomFunctions,
+} from './types/workflow';
+
+import { operators, meta } from './types/logic';
+import { arrayToObject } from './utils/utils';
+import Concurrency from './utils/concurrency';
+import Preprocessor from './preprocessor';
+import log, { Level } from './utils/logger';
+
+/**
+ * Defines optional intepreter options (passed in constructor)
+ */
+interface InterpreterOptions {
+  maxRepeats: number;
+  maxConcurrency: number;
+  serializableCallback: (output: any) => (void | Promise<void>);
+  binaryCallback: (output: any, mimeType: string) => (void | Promise<void>);
+  debug: boolean;
+  debugChannel: Partial<{
+    activeId: Function,
+    debugMessage: Function,
+  }>
+}
+
+/**
+ * Class for running the Smart Workflows.
+ */
+export default class Interpreter extends EventEmitter {
+  private workflow: Workflow;
+
+  private initializedWorkflow: Workflow | null;
+
+  private options: InterpreterOptions;
+
+  private concurrency: Concurrency;
+
+  private stopper: Function | null = null;
+
+  private log: typeof log;
+
+  constructor(workflow: WorkflowFile, options?: Partial<InterpreterOptions>) {
+    super();
+    this.workflow = workflow.workflow;
+    this.initializedWorkflow = null;
+    this.options = {
+      maxRepeats: 5,
+      maxConcurrency: 5,
+      serializableCallback: (data) => { log(JSON.stringify(data), Level.WARN); },
+      binaryCallback: () => { log('Received binary data, thrashing them.', Level.WARN); },
+      debug: false,
+      debugChannel: {},
+      ...options,
+    };
+    this.concurrency = new Concurrency(this.options.maxConcurrency);
+    this.log = (...args) => log(...args);
+
+    const error = Preprocessor.validateWorkflow(workflow);
+    if (error) {
+      throw (error);
+    }
+
+    if (this.options.debugChannel?.debugMessage) {
+      const oldLog = this.log;
+      // @ts-ignore
+      this.log = (...args: Parameters<typeof oldLog>) => {
+        if (args[1] !== Level.LOG) {
+          this.options.debugChannel.debugMessage!(typeof args[0] === 'string' ? args[0] : args[0].message);
+        }
+        oldLog(...args);
+      };
+    }
+  }
+
+  /**
+    * Returns the context object from given Page and the current workflow.\
+    * \
+    * `workflow` is used for selector extraction - function searches for used selectors to
+    * look for later in the page's context.
+    * @param page Playwright Page object
+    * @param workflow Current **initialized** workflow (array of where-what pairs).
+    * @returns {PageState} State of the current page.
+    */
+  private async getState(page: Page, workflow: Workflow): Promise<PageState> {
+    /**
+     * All the selectors present in the current Workflow
+     */
+    const selectors = Preprocessor.extractSelectors(workflow);
+
+    /**
+      * Determines whether the element targetted by the selector is [actionable](https://playwright.dev/docs/actionability).
+      * @param selector Selector to be queried
+      * @returns True if the targetted element is actionable, false otherwise.
+      */
+    const actionable = async (selector: string): Promise<boolean> => {
+      try {
+        const proms = [
+          page.isEnabled(selector, { timeout: 500 }),
+          page.isVisible(selector, { timeout: 500 }),
+        ];
+
+        return await Promise.all(proms).then((bools) => bools.every((x) => x));
+      } catch (e) {
+        // log(<Error>e, Level.ERROR);
+        return false;
+      }
+    };
+
+    /**
+      * Object of selectors present in the current page.
+      */
+    const presentSelectors: SelectorArray = await Promise.all(
+      selectors.map(async (selector) => {
+        if (await actionable(selector)) {
+          return [selector];
+        }
+        return [];
+      }),
+    ).then((x) => x.flat());
+
+    return {
+      url: page.url(),
+      cookies: (await page.context().cookies([page.url()]))
+        .reduce((p, cookie) => (
+          {
+            ...p,
+            [cookie.name]: cookie.value,
+          }), {}),
+      selectors: presentSelectors,
+    };
+  }
+
+  /**
+   * Tests if the given action is applicable with the given context.
+   * @param where Tested *where* condition
+   * @param context Current browser context.
+   * @returns True if `where` is applicable in the given context, false otherwise
+   */
+  private applicable(where: Where, context: PageState, usedActions: string[] = []): boolean {
+    /**
+     * Given two arbitrary objects, determines whether `subset` is a subset of `superset`.\
+     * \
+     * For every key in `subset`, there must be a corresponding key with equal scalar
+     * value in `superset`, or `inclusive(subset[key], superset[key])` must hold.
+     * @param subset Arbitrary non-cyclic JS object (where clause)
+     * @param superset Arbitrary non-cyclic JS object (browser context)
+     * @returns `true` if `subset <= superset`, `false` otherwise.
+     */
+    const inclusive = (subset: Record<string, unknown>, superset: Record<string, unknown>)
+      : boolean => (
+      Object.entries(subset).every(
+        ([key, value]) => {
+          /**
+           * Arrays are compared without order (are transformed into objects before comparison).
+           */
+          const parsedValue = Array.isArray(value) ? arrayToObject(value) : value;
+
+          const parsedSuperset: Record<string, unknown> = {};
+          parsedSuperset[key] = Array.isArray(superset[key])
+            ? arrayToObject(<any>superset[key])
+            : superset[key];
+
+          // Every `subset` key must exist in the `superset` and
+          // have the same value (strict equality), or subset[key] <= superset[key]
+          return parsedSuperset[key]
+            && (
+              (parsedSuperset[key] === parsedValue)
+              || ((parsedValue).constructor.name === 'RegExp' && (<RegExp>parsedValue).test(<string>parsedSuperset[key]))
+              || (
+                (parsedValue).constructor.name !== 'RegExp'
+                && typeof parsedValue === 'object' && inclusive(<typeof subset>parsedValue, <typeof superset>parsedSuperset[key])
+              )
+            );
+        },
+      )
+    );
+
+    // Every value in the "where" object should be compliant to the current state.
+    return Object.entries(where).every(
+      ([key, value]) => {
+        if (operators.includes(<any>key)) {
+          const array = Array.isArray(value)
+            ? value as Where[]
+            : Object.entries(value).map((a) => Object.fromEntries([a]));
+          // every condition is treated as a single context
+
+          switch (key as keyof typeof operators) {
+            case '$and':
+              return array?.every((x) => this.applicable(x, context));
+            case '$or':
+              return array?.some((x) => this.applicable(x, context));
+            case '$not':
+              return !this.applicable(<Where>value, context); // $not should be a unary operator
+            default:
+              throw new Error('Undefined logic operator.');
+          }
+        } else if (meta.includes(<any>key)) {
+          const testRegexString = (x: string) => {
+            if (typeof value === 'string') {
+              return x === value;
+            }
+
+            return (<RegExp><unknown>value).test(x);
+          };
+
+          switch (key as keyof typeof meta) {
+            case '$before':
+              return !usedActions.find(testRegexString);
+            case '$after':
+              return !!usedActions.find(testRegexString);
+            default:
+              throw new Error('Undefined meta operator.');
+          }
+        } else {
+          // Current key is a base condition (url, cookies, selectors)
+          return inclusive({ [key]: value }, context);
+        }
+      },
+    );
+  }
+
+  /**
+ * Given a Playwright's page object and a "declarative" list of actions, this function
+ * calls all mentioned functions on the Page object.\
+ * \
+ * Manipulates the iterator indexes (experimental feature, likely to be removed in
+ * the following versions of waw-interpreter)
+ * @param page Playwright Page object
+ * @param steps Array of actions.
+ */
+  private async carryOutSteps(page: Page, steps: What[]): Promise<void> {
+    /**
+     * Defines overloaded (or added) methods/actions usable in the workflow.
+     * If a method overloads any existing method of the Page class, it accepts the same set
+     * of parameters *(but can override some!)*\
+     * \
+     * Also, following piece of code defines functions to be run in the browser's context.
+     * Beware of false linter errors - here, we know better!
+     */
+    const wawActions: Record<CustomFunctions, (...args: any[]) => void> = {
+      screenshot: async (params: PageScreenshotOptions) => {
+        const screenshotBuffer = await page.screenshot({
+          ...params, path: undefined,
+        });
+        await this.options.binaryCallback(screenshotBuffer, 'image/png');
+      },
+      enqueueLinks: async (selector: string) => {
+        const links: string[] = await page.locator(selector)
+          .evaluateAll(
+            // @ts-ignore
+            (elements) => elements.map((a) => a.href).filter((x) => x),
+          );
+        const context = page.context();
+
+        for (const link of links) {
+          // eslint-disable-next-line
+          this.concurrency.addJob(async () => {
+            try {
+              const newPage = await context.newPage();
+              await newPage.goto(link);
+              await newPage.waitForLoadState('networkidle');
+              await this.runLoop(newPage, this.initializedWorkflow!);
+            } catch (e) {
+              // `runLoop` uses soft mode, so it recovers from it's own exceptions
+              // but newPage(), goto() and waitForLoadState() don't (and will kill
+              // the interpreter by throwing).
+              this.log(<Error>e, Level.ERROR);
+            }
+          });
+        }
+        await page.close();
+      },
+      scrape: async (selector?: string) => {
+        const scrapeResults: Record<string, string>[] = <any>await page
+          // eslint-disable-next-line
+          // @ts-ignore
+          .evaluate((s) => scrape(s ?? null), selector);
+        await this.options.serializableCallback(scrapeResults);
+      },
+      scrapeSchema: async (schema: Record<string, string>) => {
+        const handleLists = await Promise.all(
+          Object.values(schema).map((selector) => page.$$(selector)),
+        );
+
+        const namedHandleLists = Object.fromEntries(
+          Object.keys(schema).map((key, i) => [key, handleLists[i]]),
+        );
+
+        const scrapeResult = await page.evaluate((n) => scrapeSchema(n), namedHandleLists);
+
+        this.options.serializableCallback(scrapeResult);
+      },
+      scroll: async (pages?: number) => {
+        await page.evaluate(async (pagesInternal) => {
+          for (let i = 1; i <= (pagesInternal ?? 1); i += 1) {
+            // @ts-ignore
+            window.scrollTo(0, window.scrollY + window.innerHeight);
+          }
+        }, pages ?? 1);
+      },
+      script: async (code: string) => {
+        const AsyncFunction: FunctionConstructor = Object.getPrototypeOf(
+          async () => { },
+        ).constructor;
+        const x = new AsyncFunction('page', 'log', code);
+        await x(page, this.log);
+      },
+      flag: async () => new Promise((res) => {
+        this.emit('flag', page, res);
+      }),
+    };
+
+    for (const step of steps) {
+      this.log(`Launching ${step.action}`, Level.LOG);
+
+      if (step.action in wawActions) {
+        // "Arrayifying" here should not be needed (TS + syntax checker - only arrays; but why not)
+        const params = !step.args || Array.isArray(step.args) ? step.args : [step.args];
+        await wawActions[step.action as CustomFunctions](...(params ?? []));
+      } else {
+        // Implements the dot notation for the "method name" in the workflow
+        const levels = step.action.split('.');
+        const methodName = levels[levels.length - 1];
+
+        let invokee: any = page;
+        for (const level of levels.splice(0, levels.length - 1)) {
+          invokee = invokee[level];
+        }
+
+        if (!step.args || Array.isArray(step.args)) {
+          await (<any>invokee[methodName])(...(step.args ?? []));
+        } else {
+          await (<any>invokee[methodName])(step.args);
+        }
+      }
+
+      await new Promise((res) => { setTimeout(res, 500); });
+    }
+  }
+
+  private async runLoop(p: Page, workflow: Workflow) {
+    const usedActions: string[] = [];
+    let lastAction = null;
+    let repeatCount = 0;
+
+    /**
+    *  Enables the interpreter functionality for popup windows.
+    * User-requested concurrency should be entirely managed by the concurrency manager,
+    * e.g. via `enqueueLinks`.
+    */
+    p.on('popup', (popup) => {
+      this.concurrency.addJob(() => this.runLoop(popup, workflow));
+    });
+
+    /* eslint no-constant-condition: ["warn", { "checkLoops": false }] */
+    while (true) {
+      // Checks whether the page was closed from outside,
+      //  or the workflow execution has been stopped via `interpreter.stop()`
+      if (p.isClosed() || !this.stopper) {
+        return;
+      }
+
+      try {
+        await p.waitForLoadState();
+      } catch (e) {
+        await p.close();
+        return;
+      }
+
+      let pageState = {};
+      try {
+        pageState = await this.getState(p, workflow);
+      } catch (e: any) {
+        this.log('The browser has been closed.');
+        return;
+      }
+
+      if (this.options.debug) {
+        this.log(`Current state is: \n${JSON.stringify(pageState, null, 2)}`, Level.WARN);
+      }
+      const actionId = workflow.findIndex(
+        (step) => this.applicable(step.where, pageState, usedActions),
+      );
+
+      const action = workflow[actionId];
+
+      this.log(`Matched ${JSON.stringify(action?.where)}`, Level.LOG);
+
+      if (action) { // action is matched
+        if (this.options.debugChannel?.activeId) {
+          this.options.debugChannel.activeId(actionId);
+        }
+
+        repeatCount = action === lastAction ? repeatCount + 1 : 0;
+        if (this.options.maxRepeats && repeatCount >= this.options.maxRepeats) {
+          return;
+        }
+        lastAction = action;
+
+        try {
+          await this.carryOutSteps(p, action.what);
+          usedActions.push(action.id ?? 'undefined');
+        } catch (e) {
+          this.log(<Error>e, Level.ERROR);
+        }
+      } else {
+        return;
+      }
+    }
+  }
+
+  /**
+   * Spawns a browser context and runs given workflow.
+   * \
+   * Resolves after the playback is finished.
+   * @param {Page} [page] Page to run the workflow on.
+   * @param {ParamType} params Workflow specific, set of parameters
+   *  for the `{$param: nameofparam}` fields.
+   */
+  public async run(page: Page, params?: ParamType): Promise<void> {
+    if (this.stopper) {
+      throw new Error('This Interpreter is already running a workflow. To run another workflow, please, spawn another Interpreter.');
+    }
+    /**
+     * `this.workflow` with the parameters initialized.
+     */
+    this.initializedWorkflow = Preprocessor.initWorkflow(this.workflow, params);
+
+    // @ts-ignore
+    if (await page.evaluate(() => !<any>window.scrape)) {
+      page.context().addInitScript({ path: path.join(__dirname, 'browserSide', 'scraper.js') });
+    }
+
+    this.stopper = () => {
+      this.stopper = null;
+    };
+
+    this.concurrency.addJob(() => this.runLoop(page, this.initializedWorkflow!));
+
+    await this.concurrency.waitForCompletion();
+
+    this.stopper = null;
+  }
+
+  public async stop(): Promise<void> {
+    if (this.stopper) {
+      await this.stopper();
+      this.stopper = null;
+    } else {
+      throw new Error('Cannot stop, there is no running workflow!');
+    }
+  }
+}
\ No newline at end of file
diff --git a/maxun-core/preprocessor.ts b/maxun-core/preprocessor.ts
new file mode 100644
index 00000000..9ad15c2a
--- /dev/null
+++ b/maxun-core/preprocessor.ts
@@ -0,0 +1,179 @@
+import Joi from 'joi';
+import {
+  Workflow, WorkflowFile, ParamType, SelectorArray, Where,
+} from './types/workflow';
+import { operators } from './types/logic';
+
+/**
+* Class for static processing the workflow files/objects.
+*/
+export default class Preprocessor {
+  static validateWorkflow(workflow: WorkflowFile): any {
+    const regex = Joi.object({
+      $regex: Joi.string().required(),
+    });
+
+    const whereSchema = Joi.object({
+      url: [Joi.string().uri(), regex],
+      selectors: Joi.array().items(Joi.string()),
+      cookies: Joi.object({}).pattern(Joi.string(), Joi.string()),
+      $after: [Joi.string(), regex],
+      $before: [Joi.string(), regex],
+      $and: Joi.array().items(Joi.link('#whereSchema')),
+      $or: Joi.array().items(Joi.link('#whereSchema')),
+      $not: Joi.link('#whereSchema'),
+    }).id('whereSchema');
+
+    const schema = Joi.object({
+      meta: Joi.object({
+        name: Joi.string(),
+        desc: Joi.string(),
+      }),
+      workflow: Joi.array().items(
+        Joi.object({
+          id: Joi.string(),
+          where: whereSchema.required(),
+          what: Joi.array().items({
+            action: Joi.string().required(),
+            args: Joi.array().items(Joi.any()),
+          }).required(),
+        }),
+      ).required(),
+    });
+
+    const { error } = schema.validate(workflow);
+
+    return error;
+  }
+
+/**
+* Extracts parameter names from the workflow.
+* @param {WorkflowFile} workflow The given workflow
+* @returns {String[]} List of parameters' names.
+*/
+  static getParams(workflow: WorkflowFile): string[] {
+    const getParamsRecurse = (object: any): string[] => {
+      if (typeof object === 'object') {
+        // Recursion base case
+        if (object.$param) {
+          return [object.$param];
+        }
+
+        // Recursion general case
+        return Object.values(object)
+          .reduce((p: string[], v: any): string[] => [...p, ...getParamsRecurse(v)], []);
+      }
+      return [];
+    };
+
+    return getParamsRecurse(workflow.workflow);
+  }
+
+/**
+* List all the selectors used in the given workflow (only literal "selector"
+* field in WHERE clauses so far)
+*/
+  // TODO : add recursive selector search (also in click/fill etc. events?)
+  static extractSelectors(workflow: Workflow): SelectorArray {
+    /**
+* Given a Where condition, this function extracts
+* all the existing selectors from it (recursively).
+*/
+    const selectorsFromCondition = (where: Where): SelectorArray => {
+      // the `selectors` field is either on the top level
+      let out = where.selectors ?? [];
+      if (!Array.isArray(out)) {
+        out = [out];
+      }
+
+      // or nested in the "operator" array
+      operators.forEach((op) => {
+        let condWhere = where[op];
+        if (condWhere) {
+          condWhere = Array.isArray(condWhere) ? condWhere : [condWhere];
+          (condWhere).forEach((subWhere) => {
+            out = [...out, ...selectorsFromCondition(subWhere)];
+          });
+        }
+      });
+
+      return out;
+    };
+
+    // Iterate through all the steps and extract the selectors from all of them.
+    return workflow.reduce((p: SelectorArray, step) => [
+      ...p,
+      ...selectorsFromCondition(step.where).filter((x) => !p.includes(x)),
+    ], []);
+  }
+
+/**
+* Recursively crawl `object` and initializes params - replaces the `{$param : paramName}` objects
+* with the defined value.
+* @returns {Workflow} Copy of the given workflow, modified (the initial workflow is left untouched).
+*/
+  static initWorkflow(workflow: Workflow, params?: ParamType): Workflow {
+    const paramNames = this.getParams({ workflow });
+
+    if (Object.keys(params ?? {}).sort().join(',') !== paramNames.sort().join(',')) {
+      throw new Error(`Provided parameters do not match the workflow parameters
+      provided: ${Object.keys(params ?? {}).sort().join(',')},
+      expected: ${paramNames.sort().join(',')}
+      `);
+    }
+    /**
+     * A recursive method for initializing special `{key: value}` syntax objects in the workflow.
+     * @param object Workflow to initialize (or a part of it).
+     * @param k key to look for ($regex, $param)
+     * @param f function mutating the special `{}` syntax into
+     *            its true representation (RegExp...)
+     * @returns Updated object
+     */
+    const initSpecialRecurse = (
+      object: unknown,
+      k: string,
+      f: (value: string) => unknown,
+    ): unknown => {
+      if (!object || typeof object !== 'object') {
+        return object;
+      }
+
+      const out = object;
+      // for every key (child) of the object
+      Object.keys(object!).forEach((key) => {
+        // if the field has only one key, which is `k`
+        if (Object.keys((<any>object)[key]).length === 1 && (<any>object)[key][k]) {
+          // process the current special tag (init param, hydrate regex...)
+          (<any>out)[key] = f((<any>object)[key][k]);
+        } else {
+          initSpecialRecurse((<any>object)[key], k, f);
+        }
+      });
+      return out;
+    };
+
+    // TODO: do better deep copy, this is hideous.
+    let workflowCopy = JSON.parse(JSON.stringify(workflow));
+
+    if (params) {
+      workflowCopy = initSpecialRecurse(
+        workflowCopy,
+        '$param',
+        (paramName) => {
+          if (params && params[paramName]) {
+            return params[paramName];
+          }
+          throw new SyntaxError(`Unspecified parameter found ${paramName}.`);
+        },
+      );
+    }
+
+    workflowCopy = initSpecialRecurse(
+      workflowCopy,
+      '$regex',
+      (regex) => new RegExp(regex),
+    );
+
+    return <Workflow>workflowCopy;
+  }
+}
\ No newline at end of file
diff --git a/maxun-core/types/logic.ts b/maxun-core/types/logic.ts
new file mode 100644
index 00000000..5d06abbe
--- /dev/null
+++ b/maxun-core/types/logic.ts
@@ -0,0 +1,5 @@
+export const unaryOperators = ['$not'] as const;
+export const naryOperators = ['$and', '$or'] as const;
+
+export const operators = [...unaryOperators, ...naryOperators] as const;
+export const meta = ['$before', '$after'] as const;
\ No newline at end of file
diff --git a/maxun-core/types/workflow.ts b/maxun-core/types/workflow.ts
new file mode 100644
index 00000000..36c6d14d
--- /dev/null
+++ b/maxun-core/types/workflow.ts
@@ -0,0 +1,58 @@
+import { Page } from 'playwright';
+import {
+  naryOperators, unaryOperators, operators, meta,
+} from './logic';
+
+export type Operator = typeof operators[number];
+export type UnaryOperator = typeof unaryOperators[number];
+export type NAryOperator = typeof naryOperators[number];
+
+export type Meta = typeof meta[number];
+
+export type SelectorArray = string[];
+
+type RegexableString = string | { '$regex': string };
+
+type BaseConditions = {
+  'url': RegexableString,
+  'cookies': Record<string, RegexableString>,
+  'selectors': SelectorArray, // (CSS/Playwright) selectors use their own logic, there is no reason (and several technical difficulties) to allow regular expression notation
+} & Record<Meta, RegexableString>;
+
+export type Where =
+  Partial<{ [key in NAryOperator]: Where[] }> & // either a logic operator (arity N)
+  Partial<{ [key in UnaryOperator]: Where }> & // or an unary operator
+  Partial<BaseConditions>; // or one of the base conditions
+
+type MethodNames<T> = {
+  [K in keyof T]: T[K] extends Function ? K : never;
+}[keyof T];
+
+export type CustomFunctions = 'scrape' | 'scrapeSchema' | 'scroll' | 'screenshot' | 'script' | 'enqueueLinks' | 'flag';
+
+export type What = {
+  action: MethodNames<Page> | CustomFunctions,
+  args?: any[]
+};
+
+export type PageState = Partial<BaseConditions>;
+
+export type ParamType = Record<string, any>;
+
+export type MetaData = {
+  name?: string,
+  desc?: string,
+};
+
+export interface WhereWhatPair {
+  id?: string
+  where: Where
+  what: What[]
+}
+
+export type Workflow = WhereWhatPair[];
+
+export type WorkflowFile = {
+  meta?: MetaData,
+  workflow: Workflow
+};
\ No newline at end of file
diff --git a/maxun-core/utils/concurrency.ts b/maxun-core/utils/concurrency.ts
new file mode 100644
index 00000000..eec7eb33
--- /dev/null
+++ b/maxun-core/utils/concurrency.ts
@@ -0,0 +1,85 @@
+/**
+ * Concurrency class for running concurrent tasks while managing a limited amount of resources.
+ */
+export default class Concurrency {
+  /**
+     * Maximum number of workers running in parallel. If set to `null`, there is no limit.
+     */
+  maxConcurrency: number = 1;
+
+  /**
+     * Number of currently active workers.
+     */
+  activeWorkers: number = 0;
+
+  /**
+     * Queue of jobs waiting to be completed.
+     */
+  private jobQueue: Function[] = [];
+
+  /**
+     * "Resolve" callbacks of the waitForCompletion() promises.
+     */
+  private waiting: Function[] = [];
+
+  /**
+     * Constructs a new instance of concurrency manager.
+     * @param {number} maxConcurrency Maximum number of workers running in parallel.
+     */
+  constructor(maxConcurrency: number) {
+    this.maxConcurrency = maxConcurrency;
+  }
+
+  /**
+     * Takes a waiting job out of the queue and runs it.
+     */
+  private runNextJob(): void {
+    const job = this.jobQueue.pop();
+
+    if (job) {
+      // console.debug("Running a job...");
+      job().then(() => {
+        // console.debug("Job finished, running the next waiting job...");
+        this.runNextJob();
+      });
+    } else {
+      // console.debug("No waiting job found!");
+      this.activeWorkers -= 1;
+      if (this.activeWorkers === 0) {
+        // console.debug("This concurrency manager is idle!");
+        this.waiting.forEach((x) => x());
+      }
+    }
+  }
+
+  /**
+     * Pass a job (a time-demanding async function) to the concurrency manager. \
+     * The time of the job's execution depends on the concurrency manager itself
+     * (given a generous enough `maxConcurrency` value, it might be immediate,
+     * but this is not guaranteed).
+     * @param worker Async function to be executed (job to be processed).
+     */
+  addJob(job: () => Promise<any>): void {
+    // console.debug("Adding a worker!");
+    this.jobQueue.push(job);
+
+    if (!this.maxConcurrency || this.activeWorkers < this.maxConcurrency) {
+      this.runNextJob();
+      this.activeWorkers += 1;
+    } else {
+      // console.debug("No capacity to run a worker now, waiting!");
+    }
+  }
+
+  /**
+     * Waits until there is no running nor waiting job. \
+     * If the concurrency manager is idle at the time of calling this function,
+     * it waits until at least one job is compeleted (can be "presubscribed").
+     * @returns Promise, resolved after there is no running/waiting worker.
+     */
+  waitForCompletion(): Promise<void> {
+    return new Promise((res) => {
+      this.waiting.push(res);
+    });
+  }
+}
\ No newline at end of file
diff --git a/maxun-core/utils/logger.ts b/maxun-core/utils/logger.ts
new file mode 100644
index 00000000..e57421aa
--- /dev/null
+++ b/maxun-core/utils/logger.ts
@@ -0,0 +1,30 @@
+/*
+* Logger class for more detailed and comprehensible logs (with colors and timestamps)
+*/
+
+export enum Level {
+    DATE = 36,
+    LOG = 0,
+    WARN = 93,
+    ERROR = 31,
+    DEBUG = 95,
+    RESET = 0,
+  }
+  
+  export default function logger(
+    message: string | Error,
+    level: (Level.LOG | Level.WARN | Level.ERROR | Level.DEBUG) = Level.LOG,
+  ) {
+    let m = message;
+    if (message.constructor.name.includes('Error') && typeof message !== 'string') {
+      m = <Error><unknown>(message).message;
+    }
+    process.stdout.write(`\x1b[${Level.DATE}m[${(new Date()).toLocaleString()}]\x1b[0m `);
+    process.stdout.write(`\x1b[${level}m`);
+    if (level === Level.ERROR || level === Level.WARN) {
+      process.stderr.write(<string>m);
+    } else {
+      process.stdout.write(<string>m);
+    }
+    process.stdout.write(`\x1b[${Level.RESET}m\n`);
+  }
\ No newline at end of file
diff --git a/maxun-core/utils/utils.ts b/maxun-core/utils/utils.ts
new file mode 100644
index 00000000..48883dcf
--- /dev/null
+++ b/maxun-core/utils/utils.ts
@@ -0,0 +1,13 @@
+/**
+ * ESLint rule in case there is only one util function
+ * (it still does not represent the "utils" file)
+*/
+
+/* eslint-disable import/prefer-default-export */
+
+/**
+ * Converts an array of scalars to an object with **items** of the array **for keys**.
+ */
+export function arrayToObject(array : any[]) {
+    return array.reduce((p, x) => ({ ...p, [x]: [] }), {});
+  }
\ No newline at end of file