diff --git a/examples/types.yaml b/examples/types.yaml
index 9c1d793..d41fdef 100644
--- a/examples/types.yaml
+++ b/examples/types.yaml
@@ -1,57 +1,126 @@
 # Ejemplo OSINT — tipos comunes en investigacion de entidades.
 # Color como "#RRGGBB" (con o sin alpha "#RRGGBBAA").
-# Shapes: el campo `shape` se ignora — todos los nodos son circulo, salvo
-# el tipo "Table" que es cuadrado (regla de forma aplicada en
-# types_registry.cpp::apply_types_yaml).
-# Iconos: nombres ti-* mapeados en types_registry.cpp::tabler_codepoint_by_name
-# Estilos de relacion: solid | dashed | dotted
+# Shapes: campo `shape` ignorado — todos los nodos son circulo, salvo
+# el tipo "Table" que es cuadrado (regla en types_registry.cpp::apply_types_yaml).
+# Iconos: nombres ti-* mapeados en tabler_codepoint_by_name.
+# Fields: schema por tipo, formato inline-map.
+#   tipos: string | int | float | bool | date | url | enum
+#   enum requiere `values: [...]`
+#   `principal_field` (opcional) es el nombre del field que sirve de label
+#   visible en el grafo; default = "name".
 
 entities:
   - name: Person
     color: "#5B8DEF"
     icon: ti-user
+    principal_field: name
+    fields:
+      - { name: name,        type: string, required: true }
+      - { name: first_name,  type: string }
+      - { name: last_name,   type: string }
+      - { name: age,         type: int }
+      - { name: nationality, type: string }
+      - { name: birth_date,  type: date }
+      - { name: gender,      type: enum, values: [male, female, other] }
+      - { name: occupation,  type: string }
 
   - name: Email
     color: "#58CA8C"
     icon: ti-mail
+    principal_field: address
+    fields:
+      - { name: address,  type: string, required: true }
+      - { name: provider, type: string }
+      - { name: verified, type: bool }
 
   - name: Domain
     color: "#F4B860"
     icon: ti-world
+    principal_field: name
+    fields:
+      - { name: name,         type: string, required: true }
+      - { name: registrar,    type: string }
+      - { name: created_at,   type: date }
+      - { name: expires_at,   type: date }
 
   - name: Phone
     color: "#E36AC0"
     icon: ti-phone
+    principal_field: number
+    fields:
+      - { name: number,       type: string, required: true }
+      - { name: country_code, type: string }
+      - { name: kind,         type: enum, values: [mobile, landline, voip] }
 
   - name: Org
     color: "#C780E8"
     icon: ti-building
+    principal_field: name
+    fields:
+      - { name: name,    type: string, required: true }
+      - { name: country, type: string }
+      - { name: kind,    type: enum, values: [company, ngo, gov, other] }
+      - { name: website, type: url }
 
   - name: IBAN
     color: "#52CDF2"
     icon: ti-building-bank
+    principal_field: iban
+    fields:
+      - { name: iban,        type: string, required: true }
+      - { name: country,     type: string }
+      - { name: bank_name,   type: string }
 
   - name: Account
     color: "#7FD3A0"
     icon: ti-id
+    principal_field: handle
+    fields:
+      - { name: handle,    type: string, required: true }
+      - { name: platform,  type: string }
+      - { name: url,       type: url }
+      - { name: verified,  type: bool }
 
   - name: Document
     color: "#C9C9C9"
     icon: ti-file
+    principal_field: title
+    fields:
+      - { name: title,    type: string, required: true }
+      - { name: url,      type: url }
+      - { name: kind,     type: string }
+      - { name: created,  type: date }
 
   - name: Address
     color: "#FFB870"
     icon: ti-map-pin
+    principal_field: line1
+    fields:
+      - { name: line1,    type: string, required: true }
+      - { name: city,     type: string }
+      - { name: country,  type: string }
+      - { name: postcode, type: string }
 
   - name: Url
     color: "#89E0FC"
     icon: ti-link
+    principal_field: url
+    fields:
+      - { name: url,    type: url, required: true }
+      - { name: title,  type: string }
+      - { name: domain, type: string }
 
   # Nodo tabla — cuadrado (regla de forma). Issue 0010: contenedor con
   # filas que son nodos del grafo.
   - name: Table
     color: "#0EA5E9"
     icon: ti-database
+    principal_field: name
+    fields:
+      - { name: name,     type: string, required: true }
+      - { name: row_type, type: string }
+      - { name: columns,  type: string }
+      - { name: expanded, type: bool }
 
 relations:
   - name: owns
diff --git a/main.cpp b/main.cpp
index 442ad87..c4ea31f 100644
--- a/main.cpp
+++ b/main.cpp
@@ -189,9 +189,17 @@ static bool load_input() {
             g_atlas_bound = false;
             if (g_atlas) { graph_icons_destroy(g_atlas); g_atlas = nullptr; }
             g_atlas = ge::build_icon_atlas(codepoints);
+            int total_fields = 0;
+            int with_schema  = 0;
+            for (const auto& e : pt.entities) {
+                total_fields += (int)e.fields.size();
+                if (!e.fields.empty()) ++with_schema;
+            }
             std::fprintf(stdout,
-                "[graph_explorer] types.yaml: %zu entities, %zu relations, %zu icons\n",
-                pt.entities.size(), pt.relations.size(), codepoints.size());
+                "[graph_explorer] types.yaml: %zu entities (%d con schema, %d fields totales),"
+                " %zu relations, %zu icons\n",
+                pt.entities.size(), with_schema, total_fields,
+                pt.relations.size(), codepoints.size());
         }
     }
 
@@ -765,7 +773,75 @@ static void usage() {
         "       graph_explorer --input operations <path>\n"
         "       graph_explorer --types <types.yaml>\n"
         "       graph_explorer --layout force|grid|circular|radial|hierarchical|fixed\n"
-        "       graph_explorer --project <slug>\n");
+        "       graph_explorer --project <slug>\n"
+        "       graph_explorer --test-types-yaml <path>   (load+save+reload smoke test)\n");
+}
+
+// Smoke test del parser+writer (issue 0005 round-trip): carga `path`,
+// serializa a un temporal y vuelve a cargar. Compara campos clave de
+// ParsedTypes. Devuelve exit code 0 si OK, 1 si discrepancia, 2 si error.
+static int test_types_yaml_roundtrip(const char* path) {
+    ge::ParsedTypes pt1;
+    std::string err;
+    if (!ge::types_load_yaml(path, &pt1, &err)) {
+        std::fprintf(stderr, "[test] load1 fail: %s\n", err.c_str());
+        return 2;
+    }
+    std::string tmp = std::string(path) + ".roundtrip.yaml";
+    if (!ge::types_save_yaml(tmp.c_str(), pt1, &err)) {
+        std::fprintf(stderr, "[test] save fail: %s\n", err.c_str());
+        return 2;
+    }
+    ge::ParsedTypes pt2;
+    if (!ge::types_load_yaml(tmp.c_str(), &pt2, &err)) {
+        std::fprintf(stderr, "[test] load2 fail: %s\n", err.c_str());
+        return 2;
+    }
+
+    auto cmp = [&]() -> bool {
+        if (pt1.entities.size() != pt2.entities.size()) return false;
+        if (pt1.relations.size() != pt2.relations.size()) return false;
+        for (size_t i = 0; i < pt1.entities.size(); ++i) {
+            const auto& a = pt1.entities[i];
+            const auto& b = pt2.entities[i];
+            if (a.name != b.name)                       return false;
+            if (a.color != b.color)                     return false;
+            if (a.icon_name != b.icon_name)             return false;
+            if (a.principal_field != b.principal_field) return false;
+            if (a.fields.size() != b.fields.size())     return false;
+            for (size_t j = 0; j < a.fields.size(); ++j) {
+                const auto& fa = a.fields[j];
+                const auto& fb = b.fields[j];
+                if (fa.name != fb.name)             return false;
+                if (fa.kind != fb.kind)             return false;
+                if (fa.required != fb.required)     return false;
+                if (fa.enum_values != fb.enum_values) return false;
+            }
+        }
+        for (size_t i = 0; i < pt1.relations.size(); ++i) {
+            const auto& a = pt1.relations[i];
+            const auto& b = pt2.relations[i];
+            if (a.name != b.name)   return false;
+            if (a.color != b.color) return false;
+            if (a.style != b.style) return false;
+        }
+        return true;
+    };
+
+    int total_fields = 0;
+    for (const auto& e : pt1.entities) total_fields += (int)e.fields.size();
+
+    if (cmp()) {
+        std::fprintf(stdout,
+            "[test] PASS — %zu entities, %d fields, %zu relations (round-trip estable)\n",
+            pt1.entities.size(), total_fields, pt1.relations.size());
+        std::remove(tmp.c_str());
+        return 0;
+    }
+    std::fprintf(stderr,
+        "[test] FAIL — discrepancia tras round-trip. dump preservado en %s\n",
+        tmp.c_str());
+    return 1;
 }
 
 int main(int argc, char** argv) {
@@ -790,6 +866,8 @@ int main(int argc, char** argv) {
             g_layout_initial = argv[++i];
         } else if (std::strcmp(a, "--project") == 0 && i + 1 < argc) {
             project_arg = argv[++i];
+        } else if (std::strcmp(a, "--test-types-yaml") == 0 && i + 1 < argc) {
+            return test_types_yaml_roundtrip(argv[++i]);
         } else if (std::strcmp(a, "--help") == 0 || std::strcmp(a, "-h") == 0) {
             usage();
             return 0;
diff --git a/project_manager.cpp b/project_manager.cpp
index 18a7851..51d4024 100644
--- a/project_manager.cpp
+++ b/project_manager.cpp
@@ -123,29 +123,33 @@ CREATE TABLE IF NOT EXISTS logs (
 );
 )SQL";
 
-// Semilla types.yaml minima si examples/types.yaml no se encuentra.
+// Semilla types.yaml minima si examples/types.yaml no se encuentra. Incluye
+// `fields` (issue 0005) y el tipo Table como cuadrado (issue 0010 preview).
 static const char* k_seed_types_yaml = R"YAML(# types.yaml — generado al crear el proyecto. Editable desde el Type Editor.
 # Todos los nodos son circulo, salvo "Table" que es cuadrado.
-# Iconos: nombres ti-* mapeados en types_registry.cpp
-# Estilos de relacion: solid | dashed | dotted
+# Tipos de campo: string | int | float | bool | date | url | enum.
 
 entities:
   - name: Person
     color: "#5B8DEF"
     icon: ti-user
+    principal_field: name
+    fields:
+      - { name: name,       type: string, required: true }
+      - { name: first_name, type: string }
+      - { name: last_name,  type: string }
 
   - name: Email
     color: "#58CA8C"
     icon: ti-mail
+    principal_field: address
+    fields:
+      - { name: address, type: string, required: true }
 
   - name: Domain
     color: "#F4B860"
     icon: ti-world
 
-  - name: Phone
-    color: "#E36AC0"
-    icon: ti-phone
-
   - name: Org
     color: "#C780E8"
     icon: ti-building
@@ -154,10 +158,13 @@ entities:
     color: "#C9C9C9"
     icon: ti-file
 
-  # Nodo tabla — cuadrado (issue 0010).
   - name: Table
     color: "#0EA5E9"
     icon: ti-database
+    principal_field: name
+    fields:
+      - { name: name,     type: string, required: true }
+      - { name: row_type, type: string }
 
 relations:
   - name: owns