diff --git a/iparser.h b/iparser.h
index 3835e86..aa79ec5 100644
--- a/iparser.h
+++ b/iparser.h
@@ -8,10 +8,10 @@
 class IParser
 {
   public:
-	virtual std::string extractCommand(std::string cmdname, std::string content) const = 0;
-	virtual std::vector<Headline> extractHeadlines(std::string content) const = 0;
-	virtual std::string parse(const PageDao &pagedao, UrlProvider &provider, std::string content) const = 0;
-	virtual std::vector<std::string> extractCategories(std::string content) const = 0;
+	virtual std::string extractCommand(std::string cmdname, const std::string &content) const = 0;
+	virtual std::vector<Headline> extractHeadlines(const std::string &content) const = 0;
+	virtual std::string parse(const PageDao &pagedao, UrlProvider &provider, const std::string &content) const = 0;
+	virtual std::vector<std::string> extractCategories(const std::string &content) const = 0;
 
 	virtual ~IParser(){};
 };
diff --git a/parser.cpp b/parser.cpp
index ae4e9be..17e7db8 100644
--- a/parser.cpp
+++ b/parser.cpp
@@ -27,7 +27,7 @@ SOFTWARE.
 #include "parser.h"
 #include "utils.h"
 #include "htmllink.h"
-std::vector<Headline> Parser::extractHeadlines(std::string content) const
+std::vector<Headline> Parser::extractHeadlines(const std::string &content) const
 {
 	std::vector<Headline> result;
 	std::string reg = R"(\[h(1|2|3)\](.*?)\[/h\1\])";
@@ -46,7 +46,7 @@ std::vector<Headline> Parser::extractHeadlines(std::string content) const
 	return result;
 }
 
-std::vector<std::string> Parser::extractCategories(std::string content) const
+std::vector<std::string> Parser::extractCategories(const std::string &content) const
 {
 	std::vector<std::string> result;
 	std::string reg = R"(\[category\](.*?)\[/category\])";
@@ -62,7 +62,7 @@ std::vector<std::string> Parser::extractCategories(std::string content) const
 	return result;
 }
 
-std::string Parser::extractCommand(std::string cmdname, std::string content) const
+std::string Parser::extractCommand(std::string cmdname, const std::string &content) const
 {
 	std::string cmd = "[cmd:" + cmdname + "]";
 	std::string cmdend = "[/cmd:" + cmdname + "]";
@@ -116,7 +116,7 @@ std::string Parser::processLink(const PageDao &pageDao, UrlProvider &urlProvider
 	return htmllink.render();
 }
 
-std::string Parser::parse(const PageDao &pagedao, UrlProvider &provider, std::string content) const
+std::string Parser::parse(const PageDao &pagedao, UrlProvider &provider, const std::string &content) const
 {
 	std::string result;
 	// we don't care about commands, but we nevertheless replace them with empty strings
diff --git a/parser.h b/parser.h
index f34e12c..a9bb95c 100644
--- a/parser.h
+++ b/parser.h
@@ -8,10 +8,10 @@ class Parser : public IParser
 	std::string processLink(const PageDao &pageDao, UrlProvider &urlProvider, std::smatch &match) const;
 
   public:
-	std::string extractCommand(std::string cmdname, std::string content) const;
-	std::vector<Headline> extractHeadlines(std::string content) const override;
-	std::vector<std::string> extractCategories(std::string content) const override;
-	std::string parse(const PageDao &pagedao, UrlProvider &provider, std::string content) const override;
+	std::string extractCommand(std::string cmdname, const std::string &content) const;
+	std::vector<Headline> extractHeadlines(const std::string &content) const override;
+	std::vector<std::string> extractCategories(const std::string &content) const override;
+	std::string parse(const PageDao &pagedao, UrlProvider &provider, const std::string &content) const override;
 	using IParser::IParser;
 	~Parser(){};
 };