diff --git a/hgext3rd/fbamend/fold.py b/hgext3rd/fbamend/fold.py
--- a/hgext3rd/fbamend/fold.py
+++ b/hgext3rd/fbamend/fold.py
@@ -15,6 +15,7 @@
     commands,
     error,
     hg,
+    node,
     phases,
     registrar,
     scmutil,
@@ -25,6 +26,7 @@
 
 cmdtable = {}
 command = registrar.command(cmdtable)
+hex = node.hex
 
 @command('^fold|squash',
          [('r', 'rev', [], _("revision to fold")),
@@ -133,6 +135,9 @@
             phases.retractboundary(repo, tr, targetphase, [newid])
 
             replacements = {ctx.node(): (newid,) for ctx in allctx}
+            nodechanges = {fm.hexfunc(ctx.node()): [fm.hexfunc(newid)]
+                           for ctx in allctx}
+            fm.data(nodechanges=fm.formatdict(nodechanges))
             scmutil.cleanupnodes(repo, replacements, 'fold')
             fm.condwrite(not ui.quiet, 'count',
                          '%i changesets folded\n', len(revs))
diff --git a/hgext3rd/tweakdefaults.py b/hgext3rd/tweakdefaults.py
--- a/hgext3rd/tweakdefaults.py
+++ b/hgext3rd/tweakdefaults.py
@@ -794,7 +794,7 @@
     return orig(ui, repo, **opts)
 
 # set of commands which define their own formatter and prints the hash changes
-formattercommands = set()
+formattercommands = set(['fold'])
 
 def cleanupnodeswrapper(orig, repo, mapping, operation, *args, **kwargs):
     if (repo.ui.configbool('tweakdefaults', 'showupdated') and
diff --git a/tests/test-fbamend-fold.t b/tests/test-fbamend-fold.t
--- a/tests/test-fbamend-fold.t
+++ b/tests/test-fbamend-fold.t
@@ -221,3 +221,55 @@
      test1                     3:* (glob)
      test2_1                   3:* (glob)
      test2_2                   3:* (glob)
+
+Test JSON output
+  $ reset
+  $ hg debugbuilddag -m +6
+  $ hg up 5
+  1 files updated, 0 files merged, 0 files removed, 0 files unresolved
+  $ showgraph
+  @  5 r5
+  |
+  o  4 r4
+  |
+  o  3 r3
+  |
+  o  2 r2
+  |
+  o  1 r1
+  |
+  o  0 r0
+
+When rebase is not involved
+  $ hg fold --from -r '.^' -Tjson -q
+  [
+   {
+    "count": 2,
+    "nodechanges": {"aa70f0fe546a3536a4b9d49297099d140203494f": ["329a7569e12e1828787ecfebc262b012abcf7077"], "f2987ebe583896be81f8361000878a6f4b30e53a": ["329a7569e12e1828787ecfebc262b012abcf7077"]}
+   }
+  ]
+
+  $ hg fold --from -r '.^' -T '{nodechanges|json}' -q
+  {"329a7569e12e1828787ecfebc262b012abcf7077": ["befa2830d024c4b14c1d5331052d7a13ec2df124"], "cb14eba0ad9cc49472e54fe97c261f5f78a79dab": ["befa2830d024c4b14c1d5331052d7a13ec2df124"]} (no-eol)
+
+  $ showgraph
+  @  7 r3
+  |
+  o  2 r2
+  |
+  o  1 r1
+  |
+  o  0 r0
+
+XXX: maybe we also want the rebase nodechanges here.
+When rebase is involved
+  $ hg fold --exact 1 2 -Tjson -q
+  [
+   {
+    "count": 2,
+    "nodechanges": {"09bb8c08de89bca9fffcd6ed3530d6178f07d9e2": ["d65bf110c68ee2cf0a0ba076da90df3fcf76229b"], "f07e66f449d06b214d0a8a9b1a6fa8af2f5f79a5": ["d65bf110c68ee2cf0a0ba076da90df3fcf76229b"]}
+   }
+  ]
+
+  $ hg fold --exact 0 8 -T '{nodechanges|json}' -q
+  {"d65bf110c68ee2cf0a0ba076da90df3fcf76229b": ["785c10c9aad58fba814a235f074a79bdc5535083"], "fdaccbb26270c9a42503babe11fd846d7300df0b": ["785c10c9aad58fba814a235f074a79bdc5535083"]} (no-eol)