diff --git a/docs/3.results/4.table_changes.md b/docs/3.results/4.table_changes.md
index ca4f77b..5817dfd 100644
--- a/docs/3.results/4.table_changes.md
+++ b/docs/3.results/4.table_changes.md
@@ -17,9 +17,25 @@ Field types describe the structure of each field:
 
 ```typescript
 type FieldType =
-  | string                          // Primitive type name (e.g., "string", "number")
-  | Array<FieldType>                // Array of a given type
-  | { [subfield: string]: FieldType }; // Nested object
+  | string                              // Primitive type name (e.g., "string", "number")
+  | Array<StringFieldType>              // Array of a given type
+  | { [subfield: string]: StringFieldType } // Nested object
+  | import("io-ts").Mixed;              // io-ts codec at the field root
+```
+
+A field can be described either with the string-token vocabulary (primitives, arrays, nested records) or with a single [io-ts](https://github.com/gcanti/io-ts) codec at the root of the field. Codecs are not mixed inside string-tree records — use io-ts combinators (`t.type`, `t.array`, …) to nest within a codec.
+
+```typescript
+import * as t from "io-ts";
+
+const Order = {
+  fields: {
+    id: "string",
+    status: t.union([t.literal("open"), t.literal("closed")]),
+    meta: t.type({ source: t.string, retries: t.number }),
+  },
+  indexes: {},
+};
 ```
 
 ## Define Tables in a Schema
diff --git a/package.json b/package.json
index a25d153..5d3dcb7 100644
--- a/package.json
+++ b/package.json
@@ -72,6 +72,8 @@
     "@types/node": "^22.19.15",
     "@types/semver": "^7.7.1",
     "chai": "^4.5.0",
+    "fp-ts": "^2.16.0",
+    "io-ts": "^2.2.0",
     "mongodb-memory-server-core": "^11.0.1",
     "release-it": "^19.2.4",
     "release-it-changelogen": "^0.1.0",
diff --git a/pnpm-lock.yaml b/pnpm-lock.yaml
index 7b3e80e..7d66232 100644
--- a/pnpm-lock.yaml
+++ b/pnpm-lock.yaml
@@ -30,6 +30,12 @@ importers:
       chai:
         specifier: ^4.5.0
         version: 4.5.0
+      fp-ts:
+        specifier: ^2.16.0
+        version: 2.16.11
+      io-ts:
+        specifier: ^2.2.0
+        version: 2.2.22(fp-ts@2.16.11)
       mongodb-memory-server-core:
         specifier: ^11.0.1
         version: 11.0.1(socks@2.8.7)
@@ -669,6 +675,9 @@ packages:
       debug:
         optional: true
 
+  fp-ts@2.16.11:
+    resolution: {integrity: sha512-LaI+KaX2NFkfn1ZGHoKCmcfv7yrZsC3b8NtWsTVQeHkq4F27vI5igUuO53sxqDEa2gNQMHFPmpojDw/1zmUK7w==}
+
   fs-minipass@2.1.0:
     resolution: {integrity: sha512-V/JgOLFCS+R6Vcq0slCuaeWEdNC3ouDlJMNIsacH2VtALiu9mV4LPrHc5cDl8k5aw6J8jwgWWpiTo5RYhmIzvg==}
     engines: {node: '>= 8'}
@@ -740,6 +749,11 @@ packages:
       '@types/node':
         optional: true
 
+  io-ts@2.2.22:
+    resolution: {integrity: sha512-FHCCztTkHoV9mdBsHpocLpdTAfh956ZQcIkWQxxS0U5HT53vtrcuYdQneEJKH6xILaLNzXVl2Cvwtoy8XNN0AA==}
+    peerDependencies:
+      fp-ts: ^2.5.0
+
   ip-address@10.1.0:
     resolution: {integrity: sha512-XXADHxXmvT9+CRxhXg56LJovE+bmWnEWB78LB83VZTprKTmaC5QfruXocxzTZ2Kl0DNwKuBdlIhjL8LeY8Sf8Q==}
     engines: {node: '>= 12'}
@@ -1940,6 +1954,8 @@ snapshots:
     optionalDependencies:
       debug: 4.4.3
 
+  fp-ts@2.16.11: {}
+
   fs-minipass@2.1.0:
     dependencies:
       minipass: 3.3.6
@@ -2031,6 +2047,10 @@ snapshots:
     optionalDependencies:
       '@types/node': 22.19.15
 
+  io-ts@2.2.22(fp-ts@2.16.11):
+    dependencies:
+      fp-ts: 2.16.11
+
   ip-address@10.1.0: {}
 
   is-binary-path@2.1.0:
diff --git a/src/schema.ts b/src/schema.ts
index df00a51..3220747 100644
--- a/src/schema.ts
+++ b/src/schema.ts
@@ -18,10 +18,22 @@ export interface IndexDefinition {
   multi?: boolean;
 }
 
-export type FieldType =
+export type StringFieldType =
   | string
-  | Array<FieldType>
-  | { [subfield: string]: FieldType };
+  | Array<StringFieldType>
+  | { [subfield: string]: StringFieldType };
+
+interface IoTsCodec {
+  readonly _A: unknown;
+  readonly _O: unknown;
+  readonly _I: unknown;
+  readonly name: string;
+  is(u: unknown): boolean;
+  encode(a: never): unknown;
+  decode(i: unknown): unknown;
+}
+
+export type FieldType = StringFieldType | IoTsCodec;
 
 /**
  * Schema table definition
diff --git a/src/tests/datasets/codec_fields.ts b/src/tests/datasets/codec_fields.ts
new file mode 100644
index 0000000..a1346e2
--- /dev/null
+++ b/src/tests/datasets/codec_fields.ts
@@ -0,0 +1,16 @@
+import * as t from "io-ts";
+import type { SchemaDefinition } from "../../schema";
+
+export const definition: SchemaDefinition = {
+  orders: {
+    fields: {
+      id: "string",
+      status: t.union([t.literal("open"), t.literal("closed")]),
+      meta: t.type({ source: t.string, retries: t.number }),
+      tags: "string[]",
+    },
+    indexes: {
+      status: {},
+    },
+  },
+};