diff --git a/CMakeLists.txt b/CMakeLists.txt
index fd529b3e..850d6a8a 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -482,6 +482,7 @@ add_library(odgi_objs OBJECT
   ${CMAKE_SOURCE_DIR}/src/subcommand/tips_main.cpp
   ${CMAKE_SOURCE_DIR}/src/subcommand/stepindex_main.cpp
   ${CMAKE_SOURCE_DIR}/src/subcommand/heaps_main.cpp
+  ${CMAKE_SOURCE_DIR}/src/subcommand/bubble_main.cpp
   ${CMAKE_SOURCE_DIR}/src/subcommand/pav_main.cpp
   ${CMAKE_SOURCE_DIR}/src/algorithms/topological_sort.cpp
   ${CMAKE_SOURCE_DIR}/src/algorithms/kmer.cpp
@@ -535,6 +536,7 @@ add_library(odgi_objs OBJECT
   ${CMAKE_SOURCE_DIR}/src/algorithms/groom.cpp
   ${CMAKE_SOURCE_DIR}/src/algorithms/crush_n.cpp
   ${CMAKE_SOURCE_DIR}/src/algorithms/heaps.cpp
+  ${CMAKE_SOURCE_DIR}/src/algorithms/bubble.cpp
   ${CMAKE_SOURCE_DIR}/src/unittest/edge.cpp
   ${CMAKE_SOURCE_DIR}/src/algorithms/tips.cpp
   ${CMAKE_SOURCE_DIR}/src/algorithms/path_jaccard.cpp
diff --git a/src/algorithms/bubble.cpp b/src/algorithms/bubble.cpp
new file mode 100644
index 00000000..9af209cb
--- /dev/null
+++ b/src/algorithms/bubble.cpp
@@ -0,0 +1,179 @@
+#include "bubble.hpp"
+
+namespace odgi {
+
+namespace algorithms {
+
+uint64_t hash_vec(std::vector<uint64_t> const& vec) {
+    uint64_t seed = vec.size();
+    for(auto& i : vec) {
+        seed ^= i + 0x9e3779b97f4a7c15 + (seed << 6) + (seed >> 2);
+    }
+    return seed;
+}
+
+size_t hash_steps_on_handle(const PathHandleGraph& graph,
+                            const handle_t& handle) {
+    std::vector<uint64_t> v;
+    graph.for_each_step_on_handle(
+        handle,
+        [&](const step_handle_t& step) {
+            v.push_back(as_integer(graph.get_path_handle_of_step(step)));
+        });
+    std::sort(v.begin(), v.end());
+    return hash_vec(v);
+}
+
+void for_each_bubble(const PathHandleGraph& graph,
+                     const step_index_t& step_index,
+                     const path_handle_t& path,
+                     const std::function<void(const bubble_t& bubble)>& func) {
+
+    std::vector<step_hash_t> step_hashes;
+    uint64_t pos = 0;
+    graph.for_each_step_in_path(
+        path, [&](const step_handle_t& step) {
+            auto handle = graph.get_handle_of_step(step);
+            auto depth = graph.get_step_count(handle);
+            auto length = graph.get_length(handle);
+            step_hashes.push_back(
+                { step,
+                  pos,
+                  length,
+                  depth,
+                  hash_steps_on_handle(
+                      graph,
+                      handle)
+                });
+            pos += length;
+        });
+    auto j = step_hashes.begin();
+    std::vector<bubble_t> bubbles;
+    uint64_t max_bubble = 1e6;
+    for (auto i = step_hashes.begin(); i != step_hashes.end(); ++i) {
+        auto n = i;
+        uint64_t distance = 0;
+        while (++n != step_hashes.end() && n != j && distance < max_bubble) {
+            distance += n->length;
+            if (n->hash == i->hash) {
+                //bubbles.push_back({&*i, &*n});
+                i->other_tail = &*n;
+                n->other_head = &*i;
+                j = n;
+                break;
+            }
+        }
+    }
+
+    /*
+    for (auto& bubble : bubbles) {
+        std::cout << bubble.head->pos << "@" << bubble.head->depth << " "
+                  << bubble.tail->pos << "@" << bubble.tail->depth << std::endl;
+    }
+    */
+
+    for (auto i = step_hashes.begin(); i != step_hashes.end(); ++i) {
+        if (i->other_tail == nullptr || !i->other_tail->is_head_tail()) { // tail is filtered
+            uint64_t distance = 0;
+            //auto n = (std::vector<step_hash_t>::iterator)i->other_tail;
+            auto n = i;
+            while (++n != step_hashes.end() && distance < max_bubble) {
+                distance += n->length;
+                if (n->hash == i->hash
+                    && n->other_head == nullptr
+                    && n->other_tail != nullptr) {
+                    bubbles.push_back({&*i, &*n});
+                    i->other_tail = &*n;
+                    n->other_head = &*i;
+                    break;
+                }
+            }
+        } else {
+            auto n = i->other_tail;
+            bubbles.push_back({&*i, &*n});
+        }
+    }
+
+    for (auto i = step_hashes.rbegin(); i != step_hashes.rend(); ++i) {
+        if (i->other_head == nullptr || !i->other_head->is_head_tail()) { // tail is filtered
+            uint64_t distance = 0;
+            //auto n = (std::vector<step_hash_t>::iterator)i->other_tail;
+            auto n = i;
+            while (++n != step_hashes.rend() && distance < max_bubble) {
+                distance += n->length;
+                if (n->hash == i->hash
+                    && n->other_tail == nullptr
+                    && n->other_head != nullptr) {
+                    bubbles.push_back({&*n, &*i});
+                    i->other_head = &*n;
+                    n->other_tail = &*i;
+                    break;
+                }
+            }
+        } else {
+            auto n = i->other_head;
+            bubbles.push_back({&*n, &*i});
+        }
+    }
+
+    /*
+    std::vector<bubble_chain_t> chains;
+    std::vector<bool> seen(step_hashes.size());
+    for (auto i = step_hashes.begin(); i != step_hashes.end(); ++i) {
+        chains.emplace_back();
+        auto& c = chains.back().bubbles;
+        // follow the chain to the end
+        // 
+    }
+    */
+    
+    // to filter the bubbles to keep those whose head is the tail of another and vice-versa
+    /*
+    bubbles.erase(
+        std::remove_if(
+            bubbles.begin(),
+            bubbles.end(),
+            [](const bubble_t& bubble) {
+                return !(bubble.head->is_head_tail()
+                         && bubble.tail->is_head_tail());
+            }),
+        bubbles.end());
+    */
+
+    //if (false) {
+    // now draw chains
+    /*
+    std::cout << "digraph graphname {\n"
+              << "node [shape=plaintext];\n";
+        //<< "rankdir=LR;\n";
+    for (auto& bubble : bubbles) {
+        std::cout << "\"" << bubble.head->pos << "\" [label=\"" << bubble.head->pos
+                  << "@" << bubble.head->depth << "x\"];\n";
+    }
+    for (auto& bubble : bubbles) {
+        std::cout << "\"" << bubble.head->pos << "\" -> \"" << bubble.tail->pos << "\";\n";
+        //std::cout << "bubble " << bubble.head->pos << " " << bubble.head->depth << " -> " << bubble.tail->pos << " " << bubble.tail->depth << std::endl;
+        func(bubble);
+    }
+    std::cout << "}\n";
+    */
+    //}
+    std::cout << "digraph graphname {\n"
+              << "node [shape=plaintext];\n";
+    for (auto i = step_hashes.begin(); i != step_hashes.end(); ++i) {
+        std::cout << "\"" << i->pos << "\" [label=\"" << i->pos
+                  << "@" << i->depth << "x\"];\n";
+    }
+    for (auto i = step_hashes.begin(); i != step_hashes.end(); ++i) {
+        std::cout << "\"" << (i->other_head != nullptr ? std::to_string(i->other_head->pos) : "null" )
+                  << "\" -> \"" << i->pos << "\";\n";
+        std::cout << "\"" << i->pos << "\" -> \""
+                  << (i->other_tail != nullptr ? std::to_string(i->other_tail->pos) : "null"  ) << "\";\n";
+    }
+    std::cout << "}\n";
+    
+}
+
+}
+
+}
diff --git a/src/algorithms/bubble.hpp b/src/algorithms/bubble.hpp
new file mode 100644
index 00000000..b493a6b6
--- /dev/null
+++ b/src/algorithms/bubble.hpp
@@ -0,0 +1,53 @@
+#pragma once
+
+#include <iostream>
+#include <vector>
+#include <map>
+#include <set>
+#include <algorithm>
+#include <random>
+#include <omp.h>
+#include "hash_map.hpp"
+#include "position.hpp"
+#include "stepindex.hpp"
+#include <handlegraph/types.hpp>
+#include <handlegraph/iteratee.hpp>
+#include <handlegraph/util.hpp>
+#include <handlegraph/handle_graph.hpp>
+#include <handlegraph/path_handle_graph.hpp>
+#include <atomic_bitvector.hpp>
+
+namespace odgi {
+
+using namespace handlegraph;
+
+namespace algorithms {
+
+struct step_hash_t {
+    step_handle_t step;
+    uint64_t pos;
+    uint64_t length;
+    uint64_t depth;
+    uint64_t hash;
+    step_hash_t* other_tail = nullptr;
+    step_hash_t* other_head = nullptr;
+    bool is_head_tail(void) { return other_head != nullptr && other_tail != nullptr; };
+};
+
+struct bubble_t {
+    step_hash_t* head;
+    step_hash_t* tail;
+};
+
+struct bubble_chain_t {
+    std::vector<bubble_t> bubbles;
+};
+
+void for_each_bubble(const PathHandleGraph& graph,
+                     const step_index_t& step_index,
+                     const path_handle_t& path,
+                     const std::function<void(const bubble_t& bubble)>& func);
+
+}
+
+}
diff --git a/src/subcommand/bubble_main.cpp b/src/subcommand/bubble_main.cpp
new file mode 100644
index 00000000..981833aa
--- /dev/null
+++ b/src/subcommand/bubble_main.cpp
@@ -0,0 +1,104 @@
+#include "subcommand.hpp"
+#include "odgi.hpp"
+#include "args.hxx"
+#include <omp.h>
+#include "algorithms/bubble.hpp"
+#include "algorithms/stepindex.hpp"
+#include "utils.hpp"
+#include "split.hpp"
+
+namespace odgi {
+
+using namespace odgi::subcommand;
+
+int main_bubble(int argc, char **argv) {
+
+    // trick argumentparser to do the right thing with the subcommand
+    for (uint64_t i = 1; i < argc - 1; ++i) {
+        argv[i] = argv[i + 1];
+    }
+    const std::string prog_name = "odgi bubble";
+    argv[0] = (char *) prog_name.c_str();
+    --argc
+;
+    args::ArgumentParser parser("Path-based bubble detection and VCF projection.");
+    args::Group mandatory_opts(parser, "[ MANDATORY ARGUMENTS ]");
+    args::ValueFlag<std::string> og_in_file(mandatory_opts, "FILE", "Load the succinct variation graph in ODGI format from this *FILE*. The file name usually ends with *.og*. It also accepts GFAv1, but the on-the-fly conversion to the ODGI format requires additional time!", {'i', "idx"});
+    args::Group bubble_opts(parser, "[ Bubble Options ]");
+    args::ValueFlag<std::string> _target_path(bubble_opts, "NAME", "Target (reference) path name.", {'p', "target-path"});
+//    args::ValueFlag<std::string> _path_groups(bubble_opts, "FILE", "Group paths as described in two-column FILE, with columns path.name and group.name.",
+//                                              {'p', "path-groups"});
+//    args::Flag group_by_sample(bubble_opts, "bool", "Following PanSN naming (sample#hap#ctg), group by sample (1st field).", {'S', "group-by-sample"});
+//    args::Flag group_by_haplotype(bubble_opts, "bool", "Following PanSN naming (sample#hap#ctg), group by haplotype (2nd field).", {'H', "group-by-haplotype"});
+//    args::ValueFlag<std::string> _bed_targets(bubble_opts, "FILE", "BED file over path space of the graph, describing a subset of the graph to consider.",
+//                                              {'b', "bed-targets"});
+//    args::ValueFlag<uint64_t> _n_permutations(bubble_opts, "N", "Number of permutations to run.",
+//                                             {'n', "n-permutations"});
+    args::Group threading_opts(parser, "[ Threading ]");
+    args::ValueFlag<uint64_t> nthreads(threading_opts, "N", "Number of threads to use for parallel operations.",
+                                       {'t', "threads"});
+    args::Group processing_info_opts(parser, "[ Processing Information ]");
+    //args::Flag debug(processing_info_opts, "debug", "Print information about the process to stderr.", {'d', "debug"});
+    args::Flag progress(processing_info_opts, "progress", "Write the current progress to stderr.", {'P', "progress"});
+    args::Group program_info_opts(parser, "[ Program Information ]");
+    args::HelpFlag help(program_info_opts, "help", "Print a help message for odgi bubble.", {'h', "help"});
+    try {
+        parser.ParseCLI(argc, argv);
+    } catch (args::Help) {
+        std::cout << parser;
+        return 0;
+    } catch (args::ParseError e) {
+        std::cerr << e.what() << std::endl;
+        std::cerr << parser;
+        return 1;
+    }
+    if (argc == 1) {
+        std::cout << parser;
+        return 1;
+    }
+
+    if (!og_in_file) {
+        std::cerr
+            << "[odgi::bubble] error: please specify an input file from where to load the graph via -i=[FILE], --idx=[FILE]."
+            << std::endl;
+        return 1;
+    }
+
+    const uint64_t num_threads = args::get(nthreads) ? args::get(nthreads) : 1;
+    omp_set_num_threads(num_threads);
+
+    graph_t graph;
+    assert(argc > 0);
+    {
+        const std::string infile = args::get(og_in_file);
+        if (!infile.empty()) {
+            if (infile == "-") {
+                graph.deserialize(std::cin);
+            } else {
+                utils::handle_gfa_odgi_input(infile, "bubble", args::get(progress), num_threads, graph);
+            }
+        }
+    }
+
+    graph.set_number_of_threads(num_threads);
+
+    auto target_path = graph.get_path_handle(args::get(_target_path));
+    
+    algorithms::step_index_t step_index(graph, {target_path}, num_threads, true, 8);
+    //step_index.save(step_index_out_file);
+
+    //int last_depth = 0;
+    auto handle_output = [&](const algorithms::bubble_t& bubble) {
+        // 
+    };
+
+    algorithms::for_each_bubble(graph, step_index, target_path, handle_output);
+
+    return 0;
+}
+
+static Subcommand odgi_bubble("bubble", "variant detection using linearized bubbles.",
+                             PIPELINE, 3, main_bubble);
+
+
+}
diff --git a/src/subcommand/stepindex_main.cpp b/src/subcommand/stepindex_main.cpp
index 39bc96ed..ce482199 100644
--- a/src/subcommand/stepindex_main.cpp
+++ b/src/subcommand/stepindex_main.cpp
@@ -96,4 +96,4 @@ namespace odgi {
 									"Generate a step index and access the position of each step of each path once.",
 									PIPELINE, 3, main_stepindex);
 
-}
\ No newline at end of file
+}