diff --git a/include/mimalloc-internal.h b/include/mimalloc-internal.h
index 90bf6f82..feb3abae 100644
--- a/include/mimalloc-internal.h
+++ b/include/mimalloc-internal.h
@@ -148,6 +148,7 @@ mi_block_t* _mi_page_ptr_unalign(const mi_segment_t* segment, const mi_page_t* p
 bool        _mi_free_delayed_block(mi_block_t* block);
 void        _mi_block_zero_init(const mi_page_t* page, void* p, size_t size);
 size_t      _mi_path_max(void);
+void        _mi_page_block_info(const mi_page_t* page, const mi_block_t* block, mi_block_info_t* info);
 
 mi_decl_restrict void* _mi_base_malloc_zero(mi_heap_t* heap, size_t size, bool zero  MI_SOURCE_XPARAM) mi_attr_malloc mi_attr_alloc_size(2);
 void*       _mi_base_realloc_zero(mi_heap_t* heap, void* p, size_t newsize, bool zero  MI_SOURCE_XPARAM) mi_attr_alloc_size(2);
diff --git a/include/mimalloc.h b/include/mimalloc.h
index f79a4ff6..876ee89b 100644
--- a/include/mimalloc.h
+++ b/include/mimalloc.h
@@ -282,7 +282,17 @@ typedef struct mi_heap_area_s {
   size_t block_size;  // size in bytes of each block
 } mi_heap_area_t;
 
-typedef bool (mi_cdecl mi_block_visit_fun)(const mi_heap_t* heap, const mi_heap_area_t* area, void* block, size_t block_size, void* arg);
+// Information about a block
+typedef struct mi_block_info_s {
+  void*       block;          // start of the block
+  size_t      size;           // full size including padding etc.
+  size_t      usable_size;    // usable size (available for in-place realloc)
+  size_t      allocated_size; // actual allocated size (only precise in debug mode with padding)
+  bool        valid;          // is the block valid? (only detects corrupt blocks with padding enabled)
+  mi_source_t source;         // the source location that allocated this block (only valid in debug mode with padding)
+} mi_block_info_t;
+
+typedef bool (mi_cdecl mi_block_visit_fun)(const mi_heap_t* heap, const mi_heap_area_t* area, const mi_block_info_t* block_info, void* arg);
 
 mi_decl_export bool mi_heap_visit_blocks(const mi_heap_t* heap, bool visit_all_blocks, mi_block_visit_fun* visitor, void* arg);
 
diff --git a/src/alloc.c b/src/alloc.c
index ba0a5b5d..15c6e12f 100644
--- a/src/alloc.c
+++ b/src/alloc.c
@@ -18,6 +18,7 @@ terms of the MIT license. A copy of the license can be found in the file
 #include "alloc-override.c"
 #undef MI_IN_ALLOC_C
 
+#define MI_PADDING_MAX_VALIDATE   (4*1024)   // max. bytes validated for overwrites
 
 // ----------------------------------------------------------------------------------------
 // Allocation
@@ -58,7 +59,7 @@ extern inline void* _mi_page_malloc(mi_heap_t* heap, mi_page_t* page, size_t siz
   padding->delta  = (uint32_t)(delta);
   padding->source = __mi_source;
   uint8_t* fill = (uint8_t*)padding - delta;
-  const size_t maxpad = (delta > 4096 ? 4096 : delta); // set at most N initial padding bytes
+  const size_t maxpad = (delta > MI_PADDING_MAX_VALIDATE ? MI_PADDING_MAX_VALIDATE : delta); // set at most N initial padding bytes
   for (size_t i = 0; i < maxpad; i++) { fill[i] = MI_DEBUG_PADDING; }
 #endif
   return block;
@@ -211,9 +212,13 @@ static inline bool mi_check_is_double_free(const mi_page_t* page, const mi_block
 #if defined(MI_PADDING) && defined(MI_ENCODE_FREELIST)
 static void mi_check_padding(const mi_page_t* page, const mi_block_t* block);
 
-static bool mi_page_decode_padding(const mi_page_t* page, const mi_block_t* block, size_t* delta, size_t* bsize) {
+static const mi_padding_t* mi_page_get_padding(const mi_page_t* page, const mi_block_t* block, size_t* bsize) {
   *bsize = mi_page_usable_block_size(page);
-  const mi_padding_t* const padding = (mi_padding_t*)((uint8_t*)block + *bsize);
+  return (mi_padding_t*)((uint8_t*)block + *bsize);
+}
+
+static bool mi_page_decode_padding(const mi_page_t* page, const mi_block_t* block, size_t* delta, size_t* bsize) {
+  const mi_padding_t* const padding = mi_page_get_padding(page, block, bsize);
   *delta = padding->delta;
   return ((uint32_t)mi_ptr_encode(page,block,page->keys) == padding->canary && *delta <= *bsize);
 }
@@ -237,7 +242,7 @@ static bool mi_verify_padding(const mi_page_t* page, const mi_block_t* block, si
   mi_assert_internal(bsize >= delta);
   *size = bsize - delta;
   uint8_t* fill = (uint8_t*)block + bsize - delta;
-  const size_t maxpad = (delta > MI_MAX_ALIGN_SIZE ? MI_MAX_ALIGN_SIZE : delta); // check at most the first N padding bytes
+  const size_t maxpad = (delta > MI_PADDING_MAX_VALIDATE ? MI_PADDING_MAX_VALIDATE : delta); // check at most the first N padding bytes
   for (size_t i = 0; i < maxpad; i++) {
     if (fill[i] != MI_DEBUG_PADDING) {
       *wrong = bsize - delta + i;
@@ -323,6 +328,25 @@ static void mi_padding_shrink(const mi_page_t* page, const mi_block_t* block, co
 }
 #endif
 
+void _mi_page_block_info(const mi_page_t* page, const mi_block_t* block, mi_block_info_t* info) {
+  mi_assert_internal(page!=NULL);
+  mi_assert_internal(block!=NULL);
+  mi_assert_internal(info!=NULL);
+  memset(info, 0, sizeof(*info));
+  info->block = (void*)block;
+  info->size = mi_page_block_size(page);
+#if MI_PADDING
+  const mi_padding_t* padding = mi_page_get_padding(page, block, &info->usable_size);
+  info->source = padding->source;
+  size_t wrong;
+  info->valid = mi_verify_padding(page, block, &info->allocated_size, &wrong);
+#else
+  info->usable_size = mi_usable_size(block);
+  info->allocated_size = info->usable_size;
+#endif
+}
+
+
 // ------------------------------------------------------
 // Free
 // ------------------------------------------------------
diff --git a/src/heap.c b/src/heap.c
index 5d0d4b8a..ec22889b 100644
--- a/src/heap.c
+++ b/src/heap.c
@@ -468,7 +468,10 @@ static bool mi_heap_area_visit_blocks(const mi_heap_area_ex_t* xarea, mi_block_v
   if (page->capacity == 1) {
     // optimize page with one block
     mi_assert_internal(page->used == 1 && page->free == NULL);
-    return visitor(mi_page_heap(page), area, pstart, bsize, arg);
+    mi_block_info_t info;
+    mi_block_t* block = (mi_block_t*)(pstart);
+    _mi_page_block_info(page, block, &info);
+    return visitor(mi_page_heap(page), area, &info, arg);
   }
 
   // create a bitmap of free blocks.
@@ -501,8 +504,10 @@ static bool mi_heap_area_visit_blocks(const mi_heap_area_ex_t* xarea, mi_block_v
     }
     else if ((m & ((uintptr_t)1 << bit)) == 0) {
       used_count++;
-      uint8_t* block = pstart + (i * bsize);
-      if (!visitor(mi_page_heap(page), area, block, bsize, arg)) return false;
+      mi_block_info_t info;
+      mi_block_t*     block = (mi_block_t*)(pstart + (i * bsize));
+      _mi_page_block_info(page, block, &info);
+      if (!visitor(mi_page_heap(page), area, &info, arg)) return false;
     }
   }
   mi_assert_internal(page->used == used_count);
@@ -522,7 +527,7 @@ static bool mi_heap_visit_areas_page(mi_heap_t* heap, mi_page_queue_t* pq, mi_pa
   xarea.area.reserved = page->reserved * bsize;
   xarea.area.committed = page->capacity * bsize;
   xarea.area.blocks = _mi_page_start(_mi_page_segment(page), page, NULL);
-  xarea.area.used = page->used;
+  xarea.area.used = page->used * bsize;
   xarea.area.block_size = bsize;
   return fun(heap, &xarea, arg);
 }
@@ -542,7 +547,7 @@ typedef struct mi_visit_blocks_args_s {
 
 static bool mi_heap_area_visitor(const mi_heap_t* heap, const mi_heap_area_ex_t* xarea, void* arg) {
   mi_visit_blocks_args_t* args = (mi_visit_blocks_args_t*)arg;
-  if (!args->visitor(heap, &xarea->area, NULL, xarea->area.block_size, args->arg)) return false;
+  if (!args->visitor(heap, &xarea->area, NULL, args->arg)) return false;
   if (args->visit_blocks) {
     return mi_heap_area_visit_blocks(xarea, args->visitor, args->arg);
   }
diff --git a/test/main-override-static.c b/test/main-override-static.c
index 2082c024..0b5b9bf2 100644
--- a/test/main-override-static.c
+++ b/test/main-override-static.c
@@ -7,6 +7,44 @@
 #include <mimalloc.h>
 #include <mimalloc-override.h>  // redefines malloc etc.
 
+
+typedef struct mi_visit_info_s {
+  size_t area_count;
+  size_t block_count;
+} mi_visit_info_t;
+
+static bool visit(const mi_heap_t* heap, const mi_heap_area_t* area, const mi_block_info_t* info, void* arg) {
+  mi_visit_info_t* varg = (mi_visit_info_t*)(arg);
+  if (info==NULL) {
+    printf(varg->area_count==0 ? " {" : "  ]\n}\n,{");
+    varg->area_count++;
+    varg->block_count = 0;
+    printf("\"area\": %zu, \"start\": 0x%p, \"block_size\": %zu, \"used_size\": %zu,\n  \"reserved\": %zu, \"committed\": %zu,", varg->area_count, area->blocks, area->block_size, area->used, area->reserved, area->committed);
+    printf(" \"blocks\": [\n");
+  }
+  else {
+    printf(varg->block_count==0 ? "   {" : "  ,{");
+    varg->block_count++;
+    printf("\"block\": 0x%p, \"valid\": %s, \"size\": %zu, \"usable_size\": %zu, \"allocated_size\": %zu,\n    ", info->block, info->valid ? "true" : "false", info->size, info->usable_size, info->allocated_size);
+    int lineno;
+    const char* fname;
+    void* ret = mi_source_unpack(info->source, &fname, &lineno);
+    if (fname!=NULL) printf("\"source\": \"%s:%i\" }\n", fname, lineno);
+    else if (ret != NULL) printf("\"source\": \"(%p)\" }\n", ret);
+    else printf("\"source\": \"\" }\n");
+  }
+}
+
+static void mi_heap_to_json(mi_heap_t* heap) {
+  if (heap==NULL) heap = mi_heap_get_default();
+  mi_visit_info_t info = { 0, 0 };
+  printf("[\n");
+  mi_heap_visit_blocks(heap, true, &visit, &info);
+  printf(info.area_count==0 ? "]\n" : "  ] }\n]\n");
+}
+
+
+
 static void double_free1();
 static void double_free2();
 static void corrupt_free();
@@ -22,7 +60,7 @@ int main() {
   // double_free2();
   // corrupt_free();
   // block_overflow1();
-  block_overflow2();
+  // block_overflow2();
   // dangling_ptr_write();
 
   void* p1 = malloc(78);
@@ -52,7 +90,6 @@ static void block_overflow1() {
   p[18] = 0;
   free(p);
 }
-
 static void block_overflow2() {
   void* p[100];
   for (int i = 0; i < 100; i++) {