diff --git a/docs/README.md b/docs/README.md
index cf5c33d9..5526de76 100644
--- a/docs/README.md
+++ b/docs/README.md
@@ -163,6 +163,10 @@ If you want to inline sourcemap, you can try:
 tsup index.ts --sourcemap inline
 ```
 
+> Warn: Note that inline sourcemap is solely used for development, e.g. when developing a browser extension and the access to `.map` file is not allowed, and it's not recommended for production.
+
+> Warn: Source map is not supported in `--dts` build.
+
 ### Bundle formats
 
 Supported format: `esm`, `cjs`, (default) and `iife`.
diff --git a/src/cli-main.ts b/src/cli-main.ts
index edf3478f..42e1a5fd 100644
--- a/src/cli-main.ts
+++ b/src/cli-main.ts
@@ -39,8 +39,8 @@ export async function main(options: Options = {}) {
     .option('--dts-resolve', 'Resolve externals types used for d.ts files')
     .option('--dts-only', 'Emit declaration files only')
     .option(
-      '--sourcemap [option]',
-      'Generate sourcemap, "external", "inline", "both"'
+      '--sourcemap [inline]',
+      'Generate external sourcemap, or inline source: --sourcemap inline'
     )
     .option(
       '--watch [path]',
diff --git a/src/esbuild/index.ts b/src/esbuild/index.ts
index 448da15c..f4bd0cd4 100644
--- a/src/esbuild/index.ts
+++ b/src/esbuild/index.ts
@@ -237,7 +237,7 @@ export async function runEsbuild(
     logger.success(format, `⚡️ Build success in ${Math.floor(timeInMs)}ms`)
 
     await pluginContainer.buildFinished({
-      files: result.outputFiles,
+      outputFiles: result.outputFiles,
       metafile: result.metafile,
     })
   }
diff --git a/src/lib/report-size.ts b/src/lib/report-size.ts
index 3c87fa5c..f121502e 100644
--- a/src/lib/report-size.ts
+++ b/src/lib/report-size.ts
@@ -2,6 +2,7 @@ import * as colors from 'colorette'
 import { Logger } from '../log'
 
 const prettyBytes = (bytes: number) => {
+  if (bytes === 0) return '0 B'
   const unit = ['B', 'KB', 'MB', 'GB', 'TB', 'PB', 'EB', 'ZB', 'YB']
   const exp = Math.floor(Math.log(bytes) / Math.log(1024))
   return `${(bytes / Math.pow(1024, exp)).toFixed(2)} ${unit[exp]}`
diff --git a/src/options.ts b/src/options.ts
index 5be70077..df37a3d8 100644
--- a/src/options.ts
+++ b/src/options.ts
@@ -58,7 +58,7 @@ export type Options = {
     [k: string]: string
   }
   dts?: boolean | string | DtsConfig
-  sourcemap?: boolean
+  sourcemap?: boolean | 'inline'
   /** Always bundle modules matching given patterns */
   noExternal?: (string | RegExp)[]
   /** Don't bundle these modules */
diff --git a/src/plugin.ts b/src/plugin.ts
index 2237826c..c3b5269a 100644
--- a/src/plugin.ts
+++ b/src/plugin.ts
@@ -41,7 +41,7 @@ export type RenderChunk = (
 export type BuildStart = (this: PluginContext) => MaybePromise<void>
 export type BuildEnd = (
   this: PluginContext,
-  ctx: { metafile?: Metafile }
+  ctx: { writtenFiles: WrittenFile[] }
 ) => MaybePromise<void>
 
 export type ModifyEsbuildOptions = (
@@ -68,6 +68,8 @@ export type PluginContext = {
   logger: Logger
 }
 
+export type WrittenFile = { readonly name: string; readonly size: number }
+
 const parseSourceMap = (map?: string | object | null) => {
   return typeof map === 'string' ? JSON.parse(map) : map
 }
@@ -109,27 +111,31 @@ export class PluginContainer {
   }
 
   async buildFinished({
-    files,
+    outputFiles,
     metafile,
   }: {
-    files: OutputFile[]
+    outputFiles: OutputFile[]
     metafile?: Metafile
   }) {
+    const files: Array<ChunkInfo | AssetInfo> = outputFiles
+      .filter((file) => !file.path.endsWith('.map'))
+      .map((file) => {
+        if (isJS(file.path) || isCSS(file.path)) {
+          return {
+            type: 'chunk',
+            path: file.path,
+            code: file.text,
+            map: outputFiles.find((f) => f.path === `${file.path}.map`)?.text,
+          }
+        } else {
+          return { type: 'asset', path: file.path, contents: file.contents }
+        }
+      })
+
+    const writtenFiles: WrittenFile[] = []
+
     await Promise.all(
-      files.map(async (file) => {
-        const info: AssetInfo | ChunkInfo =
-          isJS(file.path) || isCSS(file.path)
-            ? {
-                type: 'chunk',
-                path: file.path,
-                code: file.text,
-                map: files.find((f) => f.path === `${file.path}.map`)?.text,
-              }
-            : {
-                type: 'asset',
-                path: file.path,
-                contents: file.contents,
-              }
+      files.map(async (info) => {
         for (const plugin of this.plugins) {
           if (info.type === 'chunk' && plugin.renderChunk) {
             const result = await plugin.renderChunk.call(
@@ -157,35 +163,67 @@ export class PluginContainer {
           }
         }
 
-        await outputFile(
-          info.path,
+        const inlineSourceMap = this.context!.options.sourcemap === 'inline'
+        const contents =
           info.type === 'chunk'
-            ? info.code + getSourcemapComment(!!info.map, info.path, isCSS(file.path))
-            : info.contents,
-          { mode: info.type === 'chunk' ? info.mode : undefined }
-        )
-        if (info.type === 'chunk' && info.map) {
+            ? info.code +
+              getSourcemapComment(
+                inlineSourceMap,
+                info.map,
+                info.path,
+                isCSS(info.path)
+              )
+            : info.contents
+        await outputFile(info.path, contents, {
+          mode: info.type === 'chunk' ? info.mode : undefined,
+        })
+        writtenFiles.push({
+          get name() {
+            return path.relative(process.cwd(), info.path)
+          },
+          get size() {
+            return contents.length
+          },
+        })
+        if (info.type === 'chunk' && info.map && !inlineSourceMap) {
           const map =
             typeof info.map === 'string' ? JSON.parse(info.map) : info.map
-          // map.sources = map.sources?.map((name: string) =>
-          //   path.relative(path.dirname(info.path), name)
-          // )
-          await outputFile(`${info.path}.map`, JSON.stringify(map))
+          const outPath = `${info.path}.map`
+          const contents = JSON.stringify(map)
+          await outputFile(outPath, contents)
+          writtenFiles.push({
+            get name() {
+              return path.relative(process.cwd(), outPath)
+            },
+            get size() {
+              return contents.length
+            },
+          })
         }
       })
     )
 
     for (const plugin of this.plugins) {
       if (plugin.buildEnd) {
-        await plugin.buildEnd.call(this.getContext(), { metafile })
+        await plugin.buildEnd.call(this.getContext(), { writtenFiles })
       }
     }
   }
 }
 
-const getSourcemapComment = (hasMap: boolean, filepath: string, isCssFile: boolean) => {
-  if (!hasMap) return ''
+const getSourcemapComment = (
+  inline: boolean,
+  map: RawSourceMap | string | null | undefined,
+  filepath: string,
+  isCssFile: boolean
+) => {
+  if (!map) return ''
   const prefix = isCssFile ? '/*' : '//'
   const suffix = isCssFile ? ' */' : ''
-  return `${prefix}# sourceMappingURL=${path.basename(filepath)}.map${suffix}`
+  const url = inline
+    ? `data:application/json;base64,${Buffer.from(
+        typeof map === 'string' ? map : JSON.stringify(map)
+      ).toString('base64')}`
+    : `${path.basename(filepath)}.map`
+  return `${prefix}# sourceMappingURL=${url}${suffix}`
 }
diff --git a/src/plugins/size-reporter.ts b/src/plugins/size-reporter.ts
index c70d1028..2239ed9f 100644
--- a/src/plugins/size-reporter.ts
+++ b/src/plugins/size-reporter.ts
@@ -5,15 +5,14 @@ export const sizeReporter = (): Plugin => {
   return {
     name: 'size-reporter',
 
-    buildEnd({ metafile }) {
-      if (!metafile) return
+    buildEnd({ writtenFiles }) {
       reportSize(
         this.logger,
         this.format,
-        Object.keys(metafile.outputs).reduce((res, name) => {
+        writtenFiles.reduce((res, file) => {
           return {
             ...res,
-            [name]: metafile!.outputs[name].bytes,
+            [file.name]: file.size,
           }
         }, {})
       )
diff --git a/test/index.test.ts b/test/index.test.ts
index c2fc109c..2abe9501 100644
--- a/test/index.test.ts
+++ b/test/index.test.ts
@@ -162,7 +162,7 @@ test('enable --dts-resolve for specific module', async (t) => {
 })
 
 test('bundle graphql-tools with --sourcemap flag', async (t) => {
-  await run(
+  const { outFiles } = await run(
     t.title,
     {
       'input.ts': `export { makeExecutableSchema } from 'graphql-tools'`,
@@ -171,11 +171,11 @@ test('bundle graphql-tools with --sourcemap flag', async (t) => {
       flags: ['--sourcemap'],
     }
   )
-  t.pass()
+  t.deepEqual(outFiles, ['input.js', 'input.js.map'])
 })
 
 test('bundle graphql-tools with --sourcemap inline flag', async (t) => {
-  const { output } = await run(
+  const { output, outFiles } = await run(
     t.title,
     {
       'input.ts': `export { makeExecutableSchema } from 'graphql-tools'`,
@@ -185,7 +185,8 @@ test('bundle graphql-tools with --sourcemap inline flag', async (t) => {
     }
   )
 
-  t.assert(output.includes('//# sourceMappingURL='))
+  t.assert(output.includes('//# sourceMappingURL=data:application/json;base64'))
+  t.deepEqual(outFiles, ['input.js'])
 })
 
 test('multiple formats', async (t) => {