diff --git a/include/zim/error.h b/include/zim/error.h
index 25f2b74b3..a0aedcff8 100644
--- a/include/zim/error.h
+++ b/include/zim/error.h
@@ -21,9 +21,9 @@
 #define ZIM_ERROR_H
 
 #include "zim.h"
+#include <tools.h>
 
 #include <stdexcept>
-#include <sstream>
 #include <typeinfo>
 
 namespace zim
@@ -135,11 +135,9 @@ namespace zim
         try {
           std::rethrow_exception(exception);
         } catch (const std::exception& e) {
-          std::stringstream ss;
-          ss << "Asynchronous error: ";
-          ss << typeid(e).name() << std::endl;
-          ss << e.what();
-          return ss.str();
+          return Formatter()
+                 << "Asynchronous error: " << typeid(e).name() << '\n'
+                 << e.what();
         } catch (...) {
           return "Unknown asynchronous exception";
         }
diff --git a/src/archive.cpp b/src/archive.cpp
index 561dc6559..3b47df4e6 100644
--- a/src/archive.cpp
+++ b/src/archive.cpp
@@ -150,9 +150,8 @@ namespace zim
   }
 
   Item Archive::getIllustrationItem(unsigned int size) const {
-    std::ostringstream ss;
-    ss  << "Illustration_" << size << "x" << size << "@" << 1;
-    auto r = m_impl->findx('M', ss.str());
+    auto r = m_impl->findx('M', Formatter() << "Illustration_" << size << "x"
+                                            << size << "@" << 1);
     if (r.first) {
       return getEntryByPath(entry_index_type(r.second)).getItem();
     }
diff --git a/src/compression.cpp b/src/compression.cpp
index f14504052..c738fa649 100644
--- a/src/compression.cpp
+++ b/src/compression.cpp
@@ -22,6 +22,7 @@
 #include "compression.h"
 
 #include "envvalue.h"
+#include "tools.h"
 
 #include <stdexcept>
 
@@ -51,9 +52,8 @@ CompStatus LZMA_INFO::stream_run(stream_t* stream, CompStep step)
     case LZMA_OK:
       return CompStatus::OK;
     default: {
-      std::ostringstream ss;
-      ss << "Unexpected lzma status : " << errcode;
-      throw std::runtime_error(ss.str());
+      throw std::runtime_error(zim::Formatter()
+                               << "Unexpected lzma status : " << errcode);
     }
   }
 }
diff --git a/src/entry.cpp b/src/entry.cpp
index 4d3e14a34..57cbf33b4 100644
--- a/src/entry.cpp
+++ b/src/entry.cpp
@@ -23,8 +23,7 @@
 #include <zim/item.h>
 #include "fileimpl.h"
 #include "log.h"
-
-#include <sstream>
+#include "tools.h"
 
 log_define("zim.entry")
 
@@ -57,14 +56,13 @@ bool Entry::isRedirect() const
 
 Item Entry::getItem(bool follow) const
 {
-  if (isRedirect()) {
-    if (! follow) {
-      std::ostringstream sstream;
-      sstream << "Entry " << getPath() << " is a redirect entry.";
-      throw InvalidType(sstream.str());
-    }
+  if (isRedirect())
+  {
+    if (!follow)
+      throw InvalidType(Formatter()
+                        << "Entry " << getPath() << " is a redirect entry.");
     return getRedirect();
- }
+  }
 
   return Item(*this);
 }
@@ -79,11 +77,10 @@ Item Entry::getRedirect() const {
 }
 
 entry_index_type Entry::getRedirectEntryIndex() const  {
-  if (!isRedirect()) {
-    std::ostringstream sstream;
-    sstream << "Entry " << getPath() << " is not a redirect entry.";
-    throw InvalidType(sstream.str());
-  }
+  if (!isRedirect())
+    throw InvalidType(Formatter()
+                      << "Entry " << getPath() << " is not a redirect entry.");
+
   return m_dirent->getRedirectIndex().v;
 }
 
diff --git a/src/file_compound.cpp b/src/file_compound.cpp
index c3fcd8262..6c3ad067a 100644
--- a/src/file_compound.cpp
+++ b/src/file_compound.cpp
@@ -19,10 +19,10 @@
  */
 
 #include "file_compound.h"
+#include "tools.h"
 
 #include <errno.h>
 #include <string.h>
-#include <sstream>
 #include <sys/stat.h>
 
 #ifdef _WIN32
@@ -61,11 +61,8 @@ FileCompound::FileCompound(const std::string& filename):
     } catch (...) { }
 
     if (empty())
-    {
-      std::ostringstream msg;
-      msg << "error " << errnoSave << " opening file \"" << filename;
-      throw std::runtime_error(msg.str());
-    }
+      throw std::runtime_error(Formatter() << "error " << errnoSave
+                                           << " opening file \"" << filename);
   }
 }
 
@@ -115,11 +112,9 @@ time_t FileCompound::getMTime() const {
     int ret = ::stat(fname, &st);
   #endif
   if (ret != 0)
-  {
-    std::ostringstream msg;
-    msg << "stat failed with errno " << errno << " : " << strerror(errno);
-    throw std::runtime_error(msg.str());
-  }
+    throw std::runtime_error(Formatter() << "stat failed with errno " << errno
+                                          << " : " << strerror(errno));
+
   mtime = st.st_mtime;
 
   return mtime;
diff --git a/src/file_reader.cpp b/src/file_reader.cpp
index 2fcf09661..af92558a8 100644
--- a/src/file_reader.cpp
+++ b/src/file_reader.cpp
@@ -22,12 +22,12 @@
 #include <zim/error.h>
 #include "file_reader.h"
 #include "file_compound.h"
+#include "tools.h"
 #include "buffer.h"
 #include <errno.h>
 #include <string.h>
 #include <cstring>
 #include <fcntl.h>
-#include <sstream>
 #include <system_error>
 #include <algorithm>
 
@@ -74,7 +74,7 @@ char MultiPartFileReader::read(offset_t offset) const {
     fhandle.readAt(&ret, zsize_t(1), physical_local_offset);
   } catch (std::runtime_error& e) {
     //Error while reading.
-    std::ostringstream s;
+    Formatter s;
     s << "Cannot read a char.\n";
     s << " - File part is " <<  part_pair->second->filename() << "\n";
     s << " - File part size is " << part_pair->second->size().v << "\n";
@@ -84,7 +84,7 @@ char MultiPartFileReader::read(offset_t offset) const {
     s << " - physical local offset is " << physical_local_offset.v << "\n";
     s << " - error is " << strerror(errno) << "\n";
     std::error_code ec(errno, std::generic_category());
-    throw std::system_error(ec, s.str());
+    throw std::system_error(ec, s);
   };
   return ret;
 }
@@ -107,7 +107,7 @@ void MultiPartFileReader::read(char* dest, offset_t offset, zsize_t size) const
     try {
       part->fhandle().readAt(dest, size_to_get, physical_local_offset);
     } catch (std::runtime_error& e) {
-      std::ostringstream s;
+      Formatter s;
       s << "Cannot read chars.\n";
       s << " - File part is " <<  part->filename() << "\n";
       s << " - File part size is " << part->size().v << "\n";
@@ -119,7 +119,7 @@ void MultiPartFileReader::read(char* dest, offset_t offset, zsize_t size) const
       s << " - physical local offset is " << physical_local_offset.v << "\n";
       s << " - error is " << strerror(errno) << "\n";
       std::error_code ec(errno, std::generic_category());
-      throw std::system_error(ec, s.str());
+      throw std::system_error(ec, s);
     };
     ASSERT(size_to_get, <=, size);
     dest += size_to_get.v;
@@ -147,13 +147,11 @@ mmapReadOnly(int fd, offset_type offset, size_type size)
 #endif
 
   const auto p = (char*)mmap(NULL, size, PROT_READ, MAP_FLAGS, fd, offset);
-  if (p == MAP_FAILED )
-  {
-    std::ostringstream s;
-    s << "Cannot mmap size " << size << " at off " << offset
-      << " : " << strerror(errno);
-    throw std::runtime_error(s.str());
-  }
+  if (p == MAP_FAILED)
+    throw std::runtime_error(Formatter()
+                             << "Cannot mmap size " << size << " at off "
+                             << offset << " : " << strerror(errno));
+
   return p;
 }
 
@@ -243,12 +241,12 @@ char FileReader::read(offset_t offset) const
     _fhandle->readAt(&ret, zsize_t(1), offset);
   } catch (std::runtime_error& e) {
     //Error while reading.
-    std::ostringstream s;
+    Formatter s;
     s << "Cannot read a char.\n";
     s << " - Reading offset at " << offset.v << "\n";
     s << " - error is " << strerror(errno) << "\n";
     std::error_code ec(errno, std::generic_category());
-    throw std::system_error(ec, s.str());
+    throw std::system_error(ec, s);
   };
   return ret;
 }
@@ -264,13 +262,13 @@ void FileReader::read(char* dest, offset_t offset, zsize_t size) const
   try {
     _fhandle->readAt(dest, size, offset);
   } catch (std::runtime_error& e) {
-    std::ostringstream s;
+    Formatter s;
     s << "Cannot read chars.\n";
     s << " - Reading offset at " << offset.v << "\n";
     s << " - size is " << size.v << "\n";
     s << " - error is " << strerror(errno) << "\n";
     std::error_code ec(errno, std::generic_category());
-    throw std::system_error(ec, s.str());
+    throw std::system_error(ec, s);
   };
 }
 
diff --git a/src/fileimpl.cpp b/src/fileimpl.cpp
index 7882d381b..e9825979f 100644
--- a/src/fileimpl.cpp
+++ b/src/fileimpl.cpp
@@ -507,11 +507,7 @@ class Grouping
   const std::string& FileImpl::getMimeType(uint16_t idx) const
   {
     if (idx >= mimeTypes.size())
-    {
-      std::ostringstream msg;
-      msg << "unknown mime type code " << idx;
-      throw ZimFileFormatError(msg.str());
-    }
+      throw ZimFileFormatError(Formatter() << "unknown mime type code " << idx);
 
     return mimeTypes[idx];
   }
diff --git a/src/fs_unix.cpp b/src/fs_unix.cpp
index 872393d3e..47c6133bb 100644
--- a/src/fs_unix.cpp
+++ b/src/fs_unix.cpp
@@ -18,8 +18,8 @@
  */
 
 #include "fs_unix.h"
+#include "tools.h"
 #include <stdexcept>
-#include <sstream>
 
 #include <sys/types.h>
 #include <sys/stat.h>
@@ -138,10 +138,7 @@ bool FS::removeFile(path_t path) {
 
 std::string getFilePathFromFD(int fd)
 {
-  std::ostringstream oss;
-  oss << "/dev/fd/" << fd;
-
-  return oss.str();
+  return Formatter()  << "/dev/fd/" << fd;
 }
 
 }; // zim namespace
diff --git a/src/fs_windows.cpp b/src/fs_windows.cpp
index 4fe568491..1322c5a4a 100644
--- a/src/fs_windows.cpp
+++ b/src/fs_windows.cpp
@@ -18,6 +18,7 @@
  */
 
 #include "fs_windows.h"
+#include "tools.h"
 #include <stdexcept>
 
 #include <windows.h>
@@ -27,7 +28,6 @@
 #include <fileapi.h>
 
 #include <iostream>
-#include <sstream>
 
 namespace zim {
 
@@ -135,11 +135,10 @@ std::unique_ptr<wchar_t[]> FS::toWideChar(path_t path)
   auto wdata = std::unique_ptr<wchar_t[]>(new wchar_t[size]);
   auto ret = MultiByteToWideChar(CP_UTF8, 0,
                 path.c_str(), -1, wdata.get(), size);
-  if (0 == ret) {
-    std::ostringstream oss;
-    oss << "Cannot convert path to wchar : " << GetLastError();
-    throw std::runtime_error(oss.str());
-  }
+  if (0 == ret)
+    throw std::runtime_error(Formatter() << "Cannot convert path to wchar : "
+                                         << GetLastError());
+
   return wdata;
 }
 
@@ -154,11 +153,10 @@ FD FS::openFile(path_t filepath)
              OPEN_EXISTING,
              FILE_ATTRIBUTE_READONLY|FILE_FLAG_RANDOM_ACCESS,
              NULL);
-  if (handle == INVALID_HANDLE_VALUE) {
-    std::ostringstream oss;
-    oss << "Cannot open file : " << GetLastError();
-    throw std::runtime_error(oss.str());
-  }
+  if (handle == INVALID_HANDLE_VALUE)
+    throw std::runtime_error(Formatter() oss << "Cannot open file : "
+                                             << GetLastError());
+
   return FD(handle);
 }
 
@@ -173,11 +171,9 @@ bool FS::makeDirectory(path_t path)
 void FS::rename(path_t old_path, path_t new_path)
 {
   auto ret = MoveFileExW(toWideChar(old_path).get(), toWideChar(new_path).get(), MOVEFILE_REPLACE_EXISTING|MOVEFILE_WRITE_THROUGH);
-  if (!ret) {
-    std::ostringstream oss;
-    oss << "Cannot move file " << old_path << " to " << new_path;
-    throw std::runtime_error(oss.str());
-  }
+  if (!ret)
+    throw std::runtime_error(Formatter() << "Cannot move file " << old_path
+                                         << " to " << new_path);
 }
 
 std::string FS::join(path_t base, path_t name)
diff --git a/src/narrowdown.h b/src/narrowdown.h
index 6ce4caf73..e3b633298 100644
--- a/src/narrowdown.h
+++ b/src/narrowdown.h
@@ -22,6 +22,7 @@
 #define ZIM_NARROWDOWN_H
 
 #include "debug.h"
+#include "tools.h"
 
 #include <algorithm>
 #include <vector>
@@ -107,11 +108,11 @@ class NarrowDown
     // It is somehow a bug and have been fixed then, but we still have to be tolerent here and accept that
     // two concecutive keys can be equal.
     if (key > nextKey) {
-      std::stringstream ss;
+      Formatter ss;
       ss << "Dirent table is not properly sorted:\n";
       ss << "  #" << i << ": " << key[0] << "/" << key.substr(1) << "\n";
       ss << "  #" << i+1 << ": " << nextKey[0] << "/" << nextKey.substr(1);
-      throw ZimFileFormatError(ss.str());
+      throw ZimFileFormatError(ss);
     }
     if ( entries.empty() ) {
       addEntry(key, i);
@@ -120,10 +121,10 @@ class NarrowDown
     {
       const std::string pseudoKey = shortestStringInBetween(key, nextKey);
       if (pred(pseudoKey, entries.back())) {
-        std::stringstream ss;
+        Formatter ss;
         ss << "Dirent table is not properly sorted:\n";
         ss << "PseudoKey " << pseudoKey << " should be after (or equal) previously generated " << pred.getKeyContent(entries.back()) << "\n";
-        throw ZimFileFormatError(ss.str());
+        throw ZimFileFormatError(ss);
       }
       ASSERT(entries.back().lindex, <, i);
       addEntry(pseudoKey, i);
diff --git a/src/version.cpp b/src/version.cpp
index 5f6b077bf..1ba5b31b9 100644
--- a/src/version.cpp
+++ b/src/version.cpp
@@ -18,7 +18,7 @@
  */
 
 #include <iostream>
-#include <sstream>
+#include "tools.h"
 
 #include <zim/version.h>
 #include <zim/zim_config.h>
@@ -45,9 +45,9 @@ namespace zim
     versions.push_back({ "libxapian", XAPIAN_VERSION });
 
     // U_ICU_VERSION does not include the patch level if 0
-    std::ostringstream libicu_version;
-    libicu_version << U_ICU_VERSION_MAJOR_NUM << "." << U_ICU_VERSION_MINOR_NUM << "." << U_ICU_VERSION_PATCHLEVEL_NUM;
-    versions.push_back({ "libicu", libicu_version.str() });
+    versions.push_back({"libicu", Formatter() << U_ICU_VERSION_MAJOR_NUM << "."
+                                              << U_ICU_VERSION_MINOR_NUM << "."
+                                              << U_ICU_VERSION_PATCHLEVEL_NUM});
 #endif
 
     return versions;
diff --git a/src/writer/cluster.cpp b/src/writer/cluster.cpp
index a70d5367e..76af1537f 100644
--- a/src/writer/cluster.cpp
+++ b/src/writer/cluster.cpp
@@ -202,10 +202,10 @@ void Cluster::write(int out_fd) const
       }
 
     default:
-      std::ostringstream msg;
+      Formatter msg;
       msg << "invalid compression flag " << static_cast<uint8_t>(getCompression());
-      log_error(msg.str());
-      throw std::runtime_error(msg.str());
+      log_error(msg);
+      throw std::runtime_error(msg);
   }
 }
 
@@ -243,12 +243,12 @@ void Cluster::write_data(writer_t writer) const
       size += blob.size();
       writer(blob);
     }
-    if (size != provider->getSize()) {
-      std::stringstream ss;
-      ss << "Declared provider's size (" << provider->getSize() << ")";
-      ss << " is not equal to total size returned by feed() calls (" << size << ").";
-      throw IncoherentImplementationError(ss.str());
-    }
+    if (size != provider->getSize())
+      throw IncoherentImplementationError(
+          Formatter()
+          << "Declared provider's size (" << provider->getSize() << ")"
+          << " is not equal to total size returned by feed() calls (" << size
+          << ").");
   }
 }
 
diff --git a/src/writer/counterHandler.cpp b/src/writer/counterHandler.cpp
index b29df05a6..795832cbb 100644
--- a/src/writer/counterHandler.cpp
+++ b/src/writer/counterHandler.cpp
@@ -45,7 +45,7 @@ DirentHandler::Dirents CounterHandler::createDirents() const {
 
 DirentHandler::ContentProviders CounterHandler::getContentProviders() const {
   ContentProviders ret;
-  std::stringstream ss;
+  Formatter ss;
   bool first = true;
   for(auto pair: m_mimetypeCounter) {
     if (! first) {
@@ -54,7 +54,7 @@ DirentHandler::ContentProviders CounterHandler::getContentProviders() const {
     ss << pair.first << "=" << pair.second;
     first = false;
   }
-  ret.push_back(std::unique_ptr<ContentProvider>(new StringProvider(ss.str())));
+  ret.push_back(std::unique_ptr<ContentProvider>(new StringProvider(ss)));
   return ret;
 }
 
diff --git a/src/writer/creator.cpp b/src/writer/creator.cpp
index 127661e6d..eee782609 100644
--- a/src/writer/creator.cpp
+++ b/src/writer/creator.cpp
@@ -190,9 +190,8 @@ namespace zim
     void Creator::addIllustration(unsigned int size, std::unique_ptr<ContentProvider> provider)
     {
       checkError();
-      std::stringstream ss;
-      ss << "Illustration_" << size << "x" << size << "@1";
-      addMetadata(ss.str(), std::move(provider), "image/png");
+      addMetadata(Formatter() << "Illustration_" << size << "x" << size << "@1",
+                  std::move(provider), "image/png");
     }
 
     void Creator::addRedirection(const std::string& path, const std::string& title, const std::string& targetPath, const Hints& hints)
@@ -213,10 +212,10 @@ namespace zim
       auto existing_dirent_it = data->dirents.find(&tmpDirent);
 
       if (existing_dirent_it == data->dirents.end()) {
-        std::ostringstream ss;
-        ss << "Impossible to alias C/" << targetPath << " as C/" << path << std::endl;
-        ss << "C/" << targetPath << " doesn't exist." << std::endl;
-        throw InvalidEntry(ss.str());
+        Formatter ss;
+        ss << "Impossible to alias C/" << targetPath << " as C/" << path << '\n';
+        ss << "C/" << targetPath << " doesn't exist." << '\n';
+        throw InvalidEntry(ss);
       }
 
       auto dirent = data->createAliasDirent(path, title, **existing_dirent_it);
@@ -543,11 +542,11 @@ namespace zim
           existing->markRemoved();
           dirents.insert(dirent);
         } else {
-          std::ostringstream ss;
-          ss << "Impossible to add " << NsAsChar(dirent->getNamespace()) << "/" << dirent->getPath() << std::endl;
-          ss << "  dirent's title to add is : " << dirent->getTitle() << std::endl;
-          ss << "  existing dirent's title is : " << existing->getTitle() << std::endl;
-          throw InvalidEntry(ss.str());
+          Formatter ss;
+          ss << "Impossible to add " << NsAsChar(dirent->getNamespace()) << "/" << dirent->getPath() << '\n';
+          ss << "  dirent's title to add is : " << dirent->getTitle() << '\n';
+          ss << "  existing dirent's title is : " << existing->getTitle() << '\n';
+          throw InvalidEntry(ss);
         }
       };
 
diff --git a/src/writer/defaultIndexData.h b/src/writer/defaultIndexData.h
index 9924c320a..ef8820177 100644
--- a/src/writer/defaultIndexData.h
+++ b/src/writer/defaultIndexData.h
@@ -60,7 +60,7 @@ namespace zim
             return;
           }
 #if defined(ENABLE_XAPIAN)
-          std::ostringstream ss;
+          Formatter ss;
           while (true) {
             auto blob = mp_contentProvider->feed();
             if(blob.size() == 0) {
@@ -70,7 +70,7 @@ namespace zim
           }
           MyHtmlParser htmlParser;
           try {
-            htmlParser.parse_html(ss.str(), "UTF-8", true);
+            htmlParser.parse_html(ss, "UTF-8", true);
           } catch(...) {}
           m_hasIndexData = !htmlParser.dump.empty() && htmlParser.indexing_allowed && (htmlParser.dump.find("NOINDEX") == std::string::npos);
           m_content = zim::removeAccents(htmlParser.dump);
diff --git a/src/writer/xapianWorker.cpp b/src/writer/xapianWorker.cpp
index eb2b5b5d1..ff4095005 100644
--- a/src/writer/xapianWorker.cpp
+++ b/src/writer/xapianWorker.cpp
@@ -63,10 +63,7 @@ namespace zim
       std::string fullPath = "C/" + m_path;
       document.set_data(fullPath);
       document.add_value(0, mp_indexData->getTitle());
-
-      std::stringstream countWordStringStream;
-      countWordStringStream << mp_indexData->getWordCount();
-      document.add_value(1, countWordStringStream.str());
+      document.add_value(1, Formatter() << mp_indexData->getWordCount());
 
       auto geoInfo = mp_indexData->getGeoPosition();
       if (std::get<0>(geoInfo)) {
diff --git a/test/creator.cpp b/test/creator.cpp
index b884dce83..3799292a3 100644
--- a/test/creator.cpp
+++ b/test/creator.cpp
@@ -358,11 +358,11 @@ TEST(ZimCreator, interruptedZimCreation)
     writer::Creator creator;
     creator.configClusterSize(16*1024);
     creator.startZimCreation(tmpFile.path());
-    std::ostringstream oss;
+    Formatter oss;
     for ( size_t i = 0; i < 12345; ++i ) {
       oss << i;
     }
-    const std::string content(oss.str());
+    const std::string content(oss);
     for ( char c = 'a'; c <= 'z'; ++c ) {
       const std::string path(1, c);
       creator.addItem(std::make_shared<TestItem>(path, path, content));
diff --git a/test/tools.h b/test/tools.h
index e65a1afed..9ff10d05b 100644
--- a/test/tools.h
+++ b/test/tools.h
@@ -36,6 +36,7 @@ typedef SSIZE_T ssize_t;
 #endif
 
 #include "../src/buffer.h"
+#include "../src/tools.h"
 #include <limits.h>
 
 #define ZIM_PRIVATE
@@ -100,9 +101,7 @@ class TempFile
 template<typename T>
 std::string to_string(const T& value)
 {
-  std::ostringstream ss;
-  ss << value;
-  return ss.str();
+  return Formatter() << value;
 }
 
 std::unique_ptr<TempFile>
diff --git a/test/uuid.cpp b/test/uuid.cpp
index abfdd822d..c59478de8 100644
--- a/test/uuid.cpp
+++ b/test/uuid.cpp
@@ -22,6 +22,7 @@
 #include <sstream>
 
 #include "gtest/gtest.h"
+#include "tools.h"
 #ifdef _WIN32
 # include <windows.h>
 # include <synchapi.h>
@@ -110,9 +111,7 @@ TEST(UuidTest, output)
 {
   zim::Uuid uuid(
       "\x55\x0e\x84\x00\xe2\x9b\x41\xd4\xa7\x16\x44\x66\x55\x44\x00\x00");
-  std::ostringstream out;
-  out << uuid;
-  std::string s = out.str();
+  std::string s = zim::unittests::to_string(uuid);
   ASSERT_EQ(s, "550e8400-e29b-41d4-a716-446655440000");
   ASSERT_EQ((std::string)uuid, "550e8400-e29b-41d4-a716-446655440000");
 }