diff --git a/packages/build/src/index.ts b/packages/build/src/index.ts
index d0b3aeb28a..5bac128ab0 100644
--- a/packages/build/src/index.ts
+++ b/packages/build/src/index.ts
@@ -1,7 +1,7 @@
 import { buildSite } from './core/main.js'
 
 // export the legacy types
-export type * from '../types/index.d.ts'
+export type * from '../types/index.js'
 
 // actual main types
 export { startDev } from './core/dev.js'
diff --git a/packages/build/types/config/inputs.d.ts b/packages/build/types/config/inputs.d.ts
index 8772165c0e..a463439737 100644
--- a/packages/build/types/config/inputs.d.ts
+++ b/packages/build/types/config/inputs.d.ts
@@ -1,4 +1,4 @@
-import type { JSONValue } from '../utils/json_value.d.ts'
+import type { JSONValue } from '../utils/json_value.js'
 
 // Helper type to be used as a workaround for the fact that `interface`s don't have implicit
 // index signatures: https://github.com/microsoft/TypeScript/issues/15300
diff --git a/packages/build/types/config/netlify_config.d.ts b/packages/build/types/config/netlify_config.d.ts
index 4a856c615a..05d30c48ea 100644
--- a/packages/build/types/config/netlify_config.d.ts
+++ b/packages/build/types/config/netlify_config.d.ts
@@ -1,8 +1,8 @@
-import type { Many } from '../utils/many.d.ts'
+import type { Many } from '../utils/many.js'
 
-import type { Build } from './build.d.ts'
-import type { Functions } from './functions.d.ts'
-import type { PluginInputs } from './inputs.d.ts'
+import type { Build } from './build.js'
+import type { Functions } from './functions.js'
+import type { PluginInputs } from './inputs.js'
 
 type HttpStatusCode = number
 
diff --git a/packages/build/types/index.d.ts b/packages/build/types/index.d.ts
index ca8860a302..8d15574374 100644
--- a/packages/build/types/index.d.ts
+++ b/packages/build/types/index.d.ts
@@ -1,7 +1,7 @@
-export type { NetlifyPlugin } from './netlify_plugin.d.ts'
-export type { NetlifyPluginOptions } from './netlify_plugin_options.d.ts'
-export type { OnBuild, OnEnd, OnError, OnPostBuild, OnPreBuild, OnSuccess } from './netlify_event_handler.d.ts'
-export type { NetlifyConfig } from './config/netlify_config.d.ts'
+export type { NetlifyPlugin } from './netlify_plugin.js'
+export type { NetlifyPluginOptions } from './netlify_plugin_options.js'
+export type { OnBuild, OnEnd, OnError, OnPostBuild, OnPreBuild, OnSuccess } from './netlify_event_handler.js'
+export type { NetlifyConfig } from './config/netlify_config.js'
 export type { NetlifyPluginUtils } from './options/netlify_plugin_utils.js'
-export type { NetlifyPluginConstants } from './netlify_plugin_constants.d.ts'
-export type { ListedFunction, ListedFunctionFile } from './options/netlify_plugin_functions_util.d.ts'
+export type { NetlifyPluginConstants } from './netlify_plugin_constants.js'
+export type { ListedFunction, ListedFunctionFile } from './options/netlify_plugin_functions_util.js'
diff --git a/packages/build/types/netlify_event_handler.d.ts b/packages/build/types/netlify_event_handler.d.ts
index 6470e6e857..cb768c1051 100644
--- a/packages/build/types/netlify_event_handler.d.ts
+++ b/packages/build/types/netlify_event_handler.d.ts
@@ -1,5 +1,5 @@
-import type { PluginInputs, StringKeys } from './config/inputs.d.ts'
-import type { NetlifyPluginOptions } from './netlify_plugin_options.d.ts'
+import type { PluginInputs, StringKeys } from './config/inputs.js'
+import type { NetlifyPluginOptions } from './netlify_plugin_options.js'
 
 interface NetlifyEventHandler<PluginOptions extends NetlifyPluginOptions = NetlifyPluginOptions> {
   (options: PluginOptions): void | Promise<void>
diff --git a/packages/build/types/netlify_plugin.d.ts b/packages/build/types/netlify_plugin.d.ts
index da1778816c..fa2d3abdab 100644
--- a/packages/build/types/netlify_plugin.d.ts
+++ b/packages/build/types/netlify_plugin.d.ts
@@ -1,5 +1,5 @@
-import type { PluginInputs } from './config/inputs.d.ts'
-import type { OnBuild, OnEnd, OnError, OnPostBuild, OnPreBuild, OnSuccess } from './netlify_event_handler.d.ts'
+import type { PluginInputs } from './config/inputs.js'
+import type { OnBuild, OnEnd, OnError, OnPostBuild, OnPreBuild, OnSuccess } from './netlify_event_handler.js'
 
 export interface NetlifyPlugin<TInputs extends PluginInputs = PluginInputs> {
   /**
diff --git a/packages/build/types/netlify_plugin_options.d.ts b/packages/build/types/netlify_plugin_options.d.ts
index 0347e9c6d8..83c1971cf4 100644
--- a/packages/build/types/netlify_plugin_options.d.ts
+++ b/packages/build/types/netlify_plugin_options.d.ts
@@ -1,8 +1,8 @@
-import type { PluginInputs, StringKeys } from './config/inputs.d.ts'
-import type { NetlifyConfig } from './config/netlify_config.d.ts'
-import type { NetlifyPluginConstants } from './netlify_plugin_constants.d.ts'
-import type { NetlifyPluginUtils } from './options/netlify_plugin_utils.d.ts'
-import type { JSONValue } from './utils/json_value.d.ts'
+import type { PluginInputs, StringKeys } from './config/inputs.js'
+import type { NetlifyConfig } from './config/netlify_config.js'
+import type { NetlifyPluginConstants } from './netlify_plugin_constants.js'
+import type { NetlifyPluginUtils } from './options/netlify_plugin_utils.js'
+import type { JSONValue } from './utils/json_value.js'
 
 export interface NetlifyPluginOptions<TInputs extends PluginInputs<StringKeys<TInputs>> = PluginInputs> {
   /**
diff --git a/packages/build/types/options/netlify_plugin_cache_util.d.ts b/packages/build/types/options/netlify_plugin_cache_util.d.ts
index 66c3e83b1c..32d471f445 100644
--- a/packages/build/types/options/netlify_plugin_cache_util.d.ts
+++ b/packages/build/types/options/netlify_plugin_cache_util.d.ts
@@ -1,4 +1,4 @@
-import type { Many } from '../utils/many.d.ts'
+import type { Many } from '../utils/many.js'
 
 /**
  * Cache files between builds
diff --git a/packages/build/types/options/netlify_plugin_utils.d.ts b/packages/build/types/options/netlify_plugin_utils.d.ts
index 0a398eabb3..94f397d0c9 100644
--- a/packages/build/types/options/netlify_plugin_utils.d.ts
+++ b/packages/build/types/options/netlify_plugin_utils.d.ts
@@ -1,9 +1,9 @@
-import type { NetlifyPluginBuildUtil } from './netlify_plugin_build_util.d.ts'
-import type { NetlifyPluginCacheUtil } from './netlify_plugin_cache_util.d.ts'
-import type { NetlifyPluginFunctionsUtil } from './netlify_plugin_functions_util.d.ts'
-import type { NetlifyPluginGitUtil } from './netlify_plugin_git_util.d.ts'
-import type { NetlifyPluginRunUtil } from './netlify_plugin_run_util.d.ts'
-import type { NetlifyPluginStatusUtil } from './netlify_plugin_status_util.d.ts'
+import type { NetlifyPluginBuildUtil } from './netlify_plugin_build_util.js'
+import type { NetlifyPluginCacheUtil } from './netlify_plugin_cache_util.js'
+import type { NetlifyPluginFunctionsUtil } from './netlify_plugin_functions_util.js'
+import type { NetlifyPluginGitUtil } from './netlify_plugin_git_util.js'
+import type { NetlifyPluginRunUtil } from './netlify_plugin_run_util.js'
+import type { NetlifyPluginStatusUtil } from './netlify_plugin_status_util.js'
 
 export interface NetlifyPluginUtils {
   build: NetlifyPluginBuildUtil