diff --git a/api/package.json b/api/package.json
index ec05dbf6c..62423d768 100644
--- a/api/package.json
+++ b/api/package.json
@@ -8,14 +8,14 @@
 	"type": "module",
 	"scripts": {
 		"validate": "yarn swagger-cli validate ./source/openapi.yaml",
-		"start": "yarn build:watch & wait-on ./dist && NODE_OPTIONS=--experimental-json-modules nodemon ./source/index.ts",
+		"start": "yarn clean && yarn build:watch & wait-on ./dist && NODE_OPTIONS=--experimental-json-modules nodemon -d 1s ./source/index.ts",
 		"build": "yarn build:openapi && yarn build:ts",
 		"build:watch": "yarn build:openapi:watch & yarn wait:openapi && yarn build:ts:watch --preserveWatchOutput",
 		"build:ts": "NODE_OPTIONS=--experimental-json-modules tsc",
 		"build:ts:watch": "yarn build:ts -w",
 		"wait:openapi": "wait-on ./source/openapi.json",
 		"build:openapi": "yarn run swagger-cli bundle ./source/openapi.yaml > ./source/openapi.json",
-		"build:openapi:watch": "nodemon -w ./source/openapi.yaml -x \"yarn build:openapi\"",
+		"build:openapi:watch": "nodemon -d 500ms -w ./source/openapi.yaml -x \"yarn build:openapi\"",
 		"clean": "rm -rf dist ./source/openapi.json"
 	},
 	"repository": {
diff --git a/api/source/index.ts b/api/source/index.ts
index 9cadb66b0..aa70056d5 100644
--- a/api/source/index.ts
+++ b/api/source/index.ts
@@ -4,8 +4,10 @@ import Koa from 'koa'
 import rules from 'modele-social'
 import Engine from 'publicodes'
 import { koaMiddleware as publicodesAPI } from 'publicodes-api'
+// @ts-ignore
 import openapi from './openapi.json'
 import { docRoutes } from './route/doc.js'
+import { openapiRoutes } from './route/openapi.js'
 
 type State = Koa.DefaultState
 
@@ -16,11 +18,9 @@ const router = new Router<State, Context>()
 
 app.use(cors())
 
-const apiRoutes = publicodesAPI(() => new Engine(rules), {
-	customOpenapi: openapi,
-})
+const apiRoutes = publicodesAPI(() => new Engine(rules))
 
-router.use('/v1', apiRoutes, docRoutes())
+router.use('/v1', apiRoutes, docRoutes(), await openapiRoutes(openapi))
 
 app.use(router.routes())
 app.use(router.allowedMethods())
diff --git a/api/source/route/openapi.ts b/api/source/route/openapi.ts
new file mode 100644
index 000000000..48e97f1f5
--- /dev/null
+++ b/api/source/route/openapi.ts
@@ -0,0 +1,27 @@
+import Router from '@koa/router'
+import { Context } from 'koa'
+import { openapi } from 'publicodes-api'
+import { mergeDeep } from '../utils.js'
+
+/**
+ * /openapi.json route, merge customOpenapi with publicodes-api openapi json
+ * @param customOpenapi
+ * @returns
+ */
+export const openapiRoutes = async (
+	customOpenapi?: Record<string, unknown>
+) => {
+	const router = new Router()
+	const publicodesOpenapi = await openapi()
+
+	const mergedOpenapi = customOpenapi
+		? mergeDeep(publicodesOpenapi, customOpenapi)
+		: publicodesOpenapi
+
+	router.get('/openapi.json', (ctx: Context) => {
+		ctx.type = 'application/json'
+		ctx.body = mergedOpenapi
+	})
+
+	return router.routes()
+}
diff --git a/api/source/utils.ts b/api/source/utils.ts
new file mode 100644
index 000000000..45417e99c
--- /dev/null
+++ b/api/source/utils.ts
@@ -0,0 +1,41 @@
+/**
+ * Simple object check.
+ * @param item
+ * @returns {boolean}
+ */
+export function isObject(item: unknown): item is Record<string, unknown> {
+	return !!item && typeof item === 'object' && !Array.isArray(item)
+}
+
+/**
+ * Deep merge two objects.
+ * @param target
+ * @param ...sources
+ */
+export function mergeDeep(
+	target: Record<string, unknown>,
+	...sources: Record<string, unknown>[]
+): Record<string, unknown> {
+	if (!sources.length) {
+		return target
+	}
+	const source = sources.shift()
+
+	if (isObject(target) && isObject(source)) {
+		for (const key in source) {
+			if (isObject(source[key])) {
+				if (!target[key]) {
+					Object.assign(target, { [key]: {} })
+				}
+				mergeDeep(
+					target[key] as Record<string, unknown>,
+					source[key] as Record<string, unknown>
+				)
+			} else {
+				Object.assign(target, { [key]: source[key] })
+			}
+		}
+	}
+
+	return mergeDeep(target, ...sources)
+}
diff --git a/api/tsconfig.json b/api/tsconfig.json
index 5e66a0b68..397d5b4b3 100644
--- a/api/tsconfig.json
+++ b/api/tsconfig.json
@@ -24,7 +24,7 @@
 		"noFallthroughCasesInSwitch": true,
 
 		/* Module Resolution Options */
-		"moduleResolution": "Node",
+		"moduleResolution": "NodeNext",
 		"esModuleInterop": true,
 		"resolveJsonModule": true,