diff --git a/bunfig.toml b/bunfig.toml
new file mode 100644
index 0000000..0f705fb
--- /dev/null
+++ b/bunfig.toml
@@ -0,0 +1,2 @@
+[test]
+preload = "./test/init.ts"
diff --git a/package.json b/package.json
index 1c2a704..b7ade4c 100644
--- a/package.json
+++ b/package.json
@@ -6,9 +6,9 @@
     "test": "bun test",
     "typecheck": "tsc --noEmit"
   },
-
   "dependencies": {
-    "log": "git+https://git.pband.ch/typescript/log.git"
+    "log": "git+https://git.pband.ch/typescript/log.git",
+    "yup": "^1.7.0"
   },
   "devDependencies": {
     "@eslint/js": "^9.35.0",
@@ -17,15 +17,15 @@
     "eslint": "^9.35.0",
     "globals": "^16.4.0",
     "jiti": "^2.5.1",
+    "logger-console": "git+https://git.pband.ch/typescript/logger-console.git",
     "prettier": "^3.6.2",
+    "tmp": "^0.2.5",
     "typescript": "^5.9.2",
     "typescript-eslint": "^8.43.0"
   },
-
   "name": "config",
   "description": "Parse configuration from env or files",
   "version": "1.0.0",
-
   "author": "Pascal Perrenoud <pascal@pband.ch>",
   "type": "module",
   "main": "./src/index.ts",
diff --git a/src/helpers.ts b/src/helpers.ts
index b73984f..088127f 100644
--- a/src/helpers.ts
+++ b/src/helpers.ts
@@ -1 +1 @@
-export type Ok<T> = {ok: true, data: T} | {ok: false}
+export type Ok<T> = {ok: true, data: T} | {ok?: false}
diff --git a/src/index.ts b/src/index.ts
index 3fbfcd6..7bedb1c 100644
--- a/src/index.ts
+++ b/src/index.ts
@@ -1,17 +1,27 @@
 import logger from 'log'
+import * as yup from 'yup'
 
-import {Ok} from './helpers'
+import * as parsing from './parsing'
+import type {Ok} from './helpers'
 
-// TODO : re-export types used to describe schema
+export * as yup from 'yup'
 
 const log = logger('config')
 
-export async function parse<S>(schema: S): Promise<Ok<unknown>> {
-    log.info("Parse configuration from env")
+export async function parse<S extends yup.Maybe<yup.AnyObject>>(schema: yup.ObjectSchema<S>): Promise<Ok<S>> {
+    log.info("Parse from env")
 
-    // TODO : Read config from env
+    log.trace("Start parsing")
+    const config = await parsing.object(schema)
+    if (!config.ok) return config
 
-    // TODO : maybe double check config
+    log.trace("double-check")
+    const res = await schema.isValid(config.data, {strict: true})
+    if (!res) {
+        log.error("Double-check failed")
+        log.debug('Config', config.data)
+        return {ok: false}
+    }
 
-    return {ok: false}
+    return config
 }
diff --git a/src/parsing.ts b/src/parsing.ts
new file mode 100644
index 0000000..50a49d3
--- /dev/null
+++ b/src/parsing.ts
@@ -0,0 +1,62 @@
+import * as yup from 'yup'
+import logger from 'log'
+
+import {read_env} from './env'
+import type {Ok} from './helpers'
+
+const log = logger('config:parsing')
+
+export async function object<S extends yup.Maybe<yup.AnyObject>>(schema: yup.ObjectSchema<S>, base_name: string = ""): Promise<Ok<S>> {
+    log.debug("Object")
+    if (base_name.length !== 0) base_name = base_name + "_"
+
+    // @ts-expect-error Ugly hack with type S
+    const data: S = {}
+    
+    for (const key in schema.fields) {
+        const sub_key = base_name + key.toUpperCase()
+
+        const sub_scheme = schema.fields[key]
+        let value: Ok<unknown>
+
+        // TODO : If array, add a transform
+        if (sub_scheme.describe().type === 'object') {
+            value = await object(sub_scheme, sub_key)
+        } else {
+            value = await generic(sub_scheme, sub_key)
+        }
+
+        if (!value.ok) return value
+        if (value.data === undefined) continue
+
+        data[key] = value.data
+    }
+
+    return {ok: true, data}
+}
+
+export async function generic<S>(scheme: yup.AnySchema<S>, key: string): Promise<Ok<S | undefined>> {
+    log.debug('Generic', scheme.describe().type)
+
+    const value = await read_env(key)
+    if (!value.ok) return value
+
+    if (value.data === undefined) {
+        const def = scheme.getDefault()
+        if (def !== undefined) return {ok: true, data: def}
+        else if (scheme.spec.optional) return {ok: true, data: undefined}
+        
+        log.warn('Missing value for', key)
+        return {}
+    }
+
+    if (!(await scheme.isValid(value.data))) {
+        log.warn('Invaid value for', key)
+        log.debug('Value:', value.data)
+        return {}
+    }
+    
+    const res = scheme.cast(value.data)
+
+    return {ok: true, data: res}
+}