diff --git a/src/apps/dbutils/cmd_negentropy.cpp b/src/apps/dbutils/cmd_negentropy.cpp
new file mode 100644
index 0000000..7b14955
--- /dev/null
+++ b/src/apps/dbutils/cmd_negentropy.cpp
@@ -0,0 +1,122 @@
+#include <iostream>
+
+#include <docopt.h>
+#include "golpe.h"
+
+#include "NegentropyFilterCache.h"
+#include "events.h"
+#include "DBQuery.h"
+
+
+static const char USAGE[] =
+R"(
+    Usage:
+      negentropy list
+      negentropy add <filter>
+      negentropy build <treeId>
+)";
+
+
+static void increaseModCounter(lmdb::txn &txn) {
+    auto m = env.lookup_Meta(txn, 1);
+    if (!m) throw herr("no Meta entry?");
+    env.update_Meta(txn, *m, { .negentropyModificationCounter = m->negentropyModificationCounter() + 1 });
+}
+
+
+void cmd_negentropy(const std::vector<std::string> &subArgs) {
+    std::map<std::string, docopt::value> args = docopt::docopt(USAGE, subArgs, true, "");
+
+    if (args["list"].asBool()) {
+        auto txn = env.txn_ro();
+
+        env.foreach_NegentropyFilter(txn, [&](auto &f){
+            auto treeId = f.primaryKeyId;
+
+            std::cout << "tree " << treeId << "\n";
+            std::cout << "  filter: " << f.filter() << "\n";
+
+            negentropy::storage::BTreeLMDB storage(txn, negentropyDbi, treeId);
+            auto size = storage.size();
+            std::cout << "  size: " << size << "\n";
+            std::cout << "  fingerprint: " << to_hex(storage.fingerprint(0, size).sv()) << "\n";
+
+            return true;
+        });
+    } else if (args["add"].asBool()) {
+        std::string filterStr = args["<filter>"].asString();
+
+        tao::json::value filterJson = tao::json::from_string(filterStr);
+        auto compiledFilter = NostrFilterGroup::unwrapped(filterJson);
+
+        if (compiledFilter.filters.size() == 1 && (compiledFilter.filters[0].since != 0 || compiledFilter.filters[0].until != MAX_U64)) {
+            throw herr("single filters should not have since/until");
+        }
+        if (compiledFilter.filters.size() == 0) throw herr("filter will never match");
+
+        filterStr = tao::json::to_string(filterJson); // make canonical
+
+        auto txn = env.txn_rw();
+        increaseModCounter(txn);
+
+        env.foreach_NegentropyFilter(txn, [&](auto &f){
+            if (f.filter() == filterStr) throw herr("filter already exists as tree: ", f.primaryKeyId);
+            return true;
+        });
+
+        uint64_t treeId = env.insert_NegentropyFilter(txn, filterStr);
+        txn.commit();
+
+        std::cout << "created tree " << treeId << "\n";
+        std::cout << "  to populate, run: strfry negentropy build " << treeId << "\n";
+    } else if (args["build"].asBool()) {
+        uint64_t treeId = args["<treeId>"].asLong();
+
+        struct Record {
+            uint64_t created_at;
+            uint8_t id[32];
+        };
+
+        std::vector<Record> recs;
+
+        auto txn = env.txn_rw(); // FIXME: split this into a read-only phase followed by a write
+        increaseModCounter(txn);
+
+        // Get filter
+
+        std::string filterStr;
+
+        {
+            auto view = env.lookup_NegentropyFilter(txn, treeId);
+            if (!view) throw herr("couldn't find treeId: ", treeId);
+            filterStr = view->filter();
+        }
+
+        // Query all matching events
+
+        DBQuery query(tao::json::from_string(filterStr));
+
+        while (1) {
+            bool complete = query.process(txn, [&](const auto &sub, uint64_t levId){
+                auto ev = lookupEventByLevId(txn, levId);
+                auto packed = PackedEventView(ev.buf);
+                recs.push_back({ packed.created_at(), });
+                memcpy(recs.back().id, packed.id().data(), 32);
+            });
+
+            if (complete) break;
+        }
+
+        // Store events in negentropy tree
+
+        negentropy::storage::BTreeLMDB storage(txn, negentropyDbi, treeId);
+
+        for (const auto &r : recs) {
+            storage.insert(r.created_at, std::string_view((char*)r.id, 32));
+        }
+
+        storage.flush();
+
+        txn.commit();
+    }
+}