diff --git a/src/search/engine.rs b/src/search/engine.rs
index 9e88606..fdbcb85 100644
--- a/src/search/engine.rs
+++ b/src/search/engine.rs
@@ -13,6 +13,32 @@ pub fn normalize_string(input_string: &str) -> String {
     string_without_double_spaces.to_lowercase()
 }
 
+/// SearchEngine represents a search engine that indexes and searches documents based on the BM25 ranking algorithm.
+/// 
+/// The search engine maintains an index of words and their frequencies in each document, as well as the actual document content.
+/// It provides methods to index documents, perform searches, and calculate relevance scores using the BM25 algorithm.
+/// 
+/// # Examples
+/// 
+/// ```
+/// use std::collections::HashMap;
+/// use rustysearch::search::engine::SearchEngine;
+/// 
+/// // Create a new search engine with k1 = 1.2 and b = 0.75
+/// let mut engine = SearchEngine::new(1.2, 0.75);
+/// 
+/// // Index a document
+/// engine.index("https://example.com/doc1", "This is the content of document 1");
+/// 
+/// // Perform a search
+/// let results = engine.search("content");
+/// 
+/// // Print the search results
+/// for (url, score) in results {
+///     println!("{} - Relevance Score: {}", url, score);
+/// }
+/// ```
+
 #[derive(Default, Debug, Clone)]
 pub struct SearchEngine {
     index: HashMap<String, HashMap<String, i32>>,
@@ -22,6 +48,16 @@ pub struct SearchEngine {
 }
 
 impl SearchEngine {
+    /// Creates a new instance of SearchEngine with the given parameters.
+    /// 
+    /// # Arguments
+    /// 
+    /// * `k1` - The k1 parameter of the BM25 algorithm.
+    /// * `b` - The b parameter of the BM25 algorithm.
+    /// 
+    /// **Returns**
+    /// 
+    /// A new instance of SearchEngine.
     pub fn new(k1: f64, b: f64) -> SearchEngine {
         SearchEngine {
             index: HashMap::new(),
@@ -31,25 +67,58 @@ impl SearchEngine {
         }
     }
 
+    /// Returns a vector of all the document URLs in the search engine's index.
+    /// 
+    /// **Returns**
+    /// 
+    /// A vector of document URLs.
     pub fn posts(&self) -> Vec<String> {
         self.documents.keys().cloned().collect()
     }
 
+    /// Returns the number of documents in the search engine's index.
+    /// 
+    /// **Returns**
+    /// 
+    /// The number of documents.
     pub fn number_of_documents(&self) -> usize {
         self.documents.len()
     }
 
+    /// Returns the average document length in terms of number of words.
+    /// 
+    /// **Returns**
+    /// 
+    /// The average document length.
     pub fn avdl(&self) -> f64 {
         let total_length: usize = self.documents.values().map(|d| d.len()).sum();
         total_length as f64 / self.documents.len() as f64
     }
 
+    /// Calculates the inverse document frequency (IDF) score for a given keyword.
+    /// 
+    /// **Arguments**
+    /// 
+    /// * `kw` - The keyword for which to calculate the IDF score.
+    /// 
+    /// **Returns**
+    /// 
+    /// The IDF score.
     pub fn idf(&self, kw: &str) -> f64 {
         let n = self.number_of_documents() as f64;
         let n_kw = self.get_urls(kw).len() as f64;
         ((n - n_kw + 0.5) / (n_kw + 0.5) + 1.0).ln()
     }
 
+    /// Calculates the BM25 relevance scores for a given keyword.
+    /// 
+    /// **Arguments**
+    /// 
+    /// * `kw` - The keyword for which to calculate the relevance scores.
+    /// 
+    /// **Returns**
+    /// 
+    /// A HashMap containing the document URLs as keys and their relevance scores as values.
     pub fn bm25(&self, kw: &str) -> HashMap<String, f64> {
         let mut result = HashMap::new();
         let idf_score = self.idf(kw);
@@ -62,6 +131,15 @@ impl SearchEngine {
         result
     }
 
+    /// Performs a search for the given query and returns the relevance scores for the matching documents.
+    /// 
+    /// **Arguments**
+    /// 
+    /// * `query` - The search query.
+    /// 
+    /// **Returns**
+    /// 
+    /// A HashMap containing the document URLs as keys and their relevance scores as values.
     pub fn search(&mut self, query: &str) -> HashMap<String, f64> {
         let keywords = normalize_string(query).split_whitespace().map(|s| s.to_string()).collect::<Vec<String>>();
         let mut url_scores: HashMap<String, f64> = HashMap::new();
@@ -72,6 +150,12 @@ impl SearchEngine {
         url_scores
     }
 
+    /// Indexes a document with the given URL and content.
+    /// 
+    /// **Arguments**
+    /// 
+    /// * `url` - The URL of the document.
+    /// * `content` - The content of the document.
     pub fn index(&mut self, url: &str, content: &str) {
         self.documents.insert(url.to_string(), content.to_string());
         let words = normalize_string(content).split_whitespace().map(|s| s.to_string()).collect::<Vec<String>>();
@@ -80,17 +164,32 @@ impl SearchEngine {
         }
     }
 
+    /// Bulk indexes multiple documents.
+    /// 
+    /// **Arguments**
+    /// 
+    /// * `documents` - A vector of tuples containing the URL and content of each document.
     pub fn bulk_index(&mut self, documents: Vec<(&str, &str)>) {
         for (url, content) in documents {
             self.index(url, content);
         }
     }
 
+    /// Returns the URLs and frequencies of a given keyword in the search engine's index.
+    /// 
+    /// **Arguments**
+    /// 
+    /// * `keyword` - The keyword to search for.
+    /// 
+    /// **Returns**
+    /// 
+    /// A HashMap containing the document URLs as keys and their frequencies as values.
     pub fn get_urls(&self, keyword: &str) -> HashMap<String, i32> {
         let keyword = normalize_string(keyword);
         self.index.get(&keyword).cloned().unwrap_or(HashMap::new())
     }
 
+    /// Prints the current state of the search engine's index and document collection for debugging purposes.
     pub fn debug_index(&self) {
         log::debug!("Index: {:?}", self.index);
         log::debug!("Documents: {:?}", self.documents);