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diff --git a/src/Hird.php b/src/Hird.php
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+<?php
+
+declare(strict_types=1);
+
+namespace Askonomm\Hird;
+
+use Askonomm\Hird\Validators\Validator;
+use Askonomm\Hird\Validators\LenValidator;
+use Askonomm\Hird\Validators\EmailValidator;
+use Askonomm\Hird\Validators\RequiredValidator;
+
+/**
+ * Hird takes in an array of `$fields` and an array of  
+ * `$rules`.
+ * 
+ * The key of each item in the `$fields` array must correspond to the 
+ * the key of each item in the `$rules` array, so that Bouncer 
+ * would know how to connect the two to each other.
+ * 
+ * The `$rules` must have a value that is a string where the rules
+ * are separated by a `|` character, and each rule must match the key of
+ * the implemented validator, such as `len`, `email` or one that you have 
+ * implemented yourself. Additionally, each rule can take in a modifier, 
+ * where the name of the rule and the modifier is separated by a `:` character.
+ * 
+ * For example, say we have a validator called `len` which takes a modifier that
+ * lets that validator validate the length of a string, in such a case we'd write
+ * that rule as `len:8`, which would indicate using a `len` validator and passing 
+ * a modifier with the value `8` to it. 
+ * 
+ * Example usage of Hird: 
+ * 
+ * ```php
+ * $fields = ['email' => 'asko@bien.ee'];
+ * $rules = ['email' => 'required|email'];
+ * $hird = new Hird($fields, $rules);
+ * 
+ * if ($hird->fails()) {
+ *  return $hird->errors();
+ * }
+ * ```
+ * 
+ * @author Asko Nomm <asko@bien.ee>
+ */
+class Hird
+{
+    private array $errors = [];
+    private array $validators = [];
+
+    public function __construct(
+        private array $fields,
+        private array $rules,
+    ) {
+        $this->registerDefaultValidators();
+        $this->validate();
+    }
+
+    /**
+     * Registers the default, built-in validators.
+     *
+     * @return void
+     */
+    private function registerDefaultValidators(): void
+    {
+        $this->registerValidator('len', (new LenValidator));
+        $this->registerValidator('email', (new EmailValidator));
+        $this->registerValidator('required', (new RequiredValidator));
+    }
+
+    /**
+     * Registers a validator to a `$ruleName`.
+     *
+     * @param string $ruleName
+     * @param Validator $validator
+     * @return void
+     */
+    public function registerValidator(string $ruleName, Validator $validator): void
+    {
+        $this->validators[$ruleName] = $validator;
+    }
+
+    /**
+     * Removes a validator assigned to the `$ruleName`.
+     *
+     * @param string $ruleName
+     * @return void
+     */
+    public function removeValidator(string $ruleName): void
+    {
+        unset($this->validators[$ruleName]);
+    }
+
+    /**
+     * Runs `$this->rules` over `$this->fields` to construct 
+     * potential errors that will be stored as an array of strings 
+     * in `$this->errors`.
+     *
+     * @return void
+     */
+    private function validate(): void
+    {
+        foreach ($this->rules as $field => $rule) {
+            $value = $this->fields[$field];
+
+            foreach (explode('|', $rule) as $item) {
+                if (str_contains($item, ':')) {
+                    [$name, $modifier] = explode(':', $item);
+
+                    if (!$this->validators[$name]->validate($value, $modifier)) {
+                        $this->errors[] = $this->validators[$name]->composeError($field, $modifier);
+                    }
+                } else {
+                    if (!$this->validators[$item]->validate($value)) {
+                        $this->errors[] = $this->validators[$item]->composeError($field);
+                    }
+                }
+            }
+        }
+    }
+
+    /**
+     * Returns a boolean `true` if there have been any errors.
+     * Returns `false` otherwise.
+     *
+     * @return boolean
+     */
+    public function fails(): bool
+    {
+        return count($this->errors) !== 0;
+    }
+
+    /**
+     * Returns an array of strings where each string 
+     * is a single error that happened during validation.
+     * 
+     * @return array
+     */
+    public function errors(): array
+    {
+        return $this->errors;
+    }
+
+    /**
+     * If errors are present, returns the first one.
+     * Otherwise returns an empty string.
+     *
+     * @return string
+     */
+    public function firstError(): string
+    {
+        if (count($this->errors) > 0) {
+            return $this->errors[0];
+        }
+
+        return '';
+    }
+}