diff --git a/apps/sim/tools/knowledge/create_document.ts b/apps/sim/tools/knowledge/create_document.ts
index 5b82d504a7..e209a0e9bd 100644
--- a/apps/sim/tools/knowledge/create_document.ts
+++ b/apps/sim/tools/knowledge/create_document.ts
@@ -1,4 +1,7 @@
-import type { KnowledgeCreateDocumentResponse } from '@/tools/knowledge/types'
+import {
+  inferDocumentFileInfo,
+  type KnowledgeCreateDocumentResponse,
+} from '@/tools/knowledge/types'
 import { enrichKBTagsSchema } from '@/tools/schema-enrichers'
 import { formatDocumentTagsForAPI, parseDocumentTags } from '@/tools/shared/tags'
 import type { ToolConfig } from '@/tools/types'
@@ -63,30 +66,36 @@ export const knowledgeCreateDocumentTool: ToolConfig<any, KnowledgeCreateDocumen
       if (!textContent || textContent.length < 1) {
         throw new Error('Document content cannot be empty')
       }
-      if (textContent.length > 1000000) {
+      const utf8Bytes = new TextEncoder().encode(textContent)
+      const contentBytes = utf8Bytes.length
+
+      if (contentBytes > 1_000_000) {
         throw new Error('Document content exceeds maximum size of 1MB')
       }
 
-      const contentBytes = new TextEncoder().encode(textContent).length
-
-      const utf8Bytes = new TextEncoder().encode(textContent)
-      const base64Content =
-        typeof Buffer !== 'undefined'
-          ? Buffer.from(textContent, 'utf8').toString('base64')
-          : btoa(String.fromCharCode(...utf8Bytes))
+      let base64Content: string
+      if (typeof Buffer !== 'undefined') {
+        base64Content = Buffer.from(textContent, 'utf8').toString('base64')
+      } else {
+        let binary = ''
+        for (let i = 0; i < utf8Bytes.length; i++) {
+          binary += String.fromCharCode(utf8Bytes[i])
+        }
+        base64Content = btoa(binary)
+      }
 
-      const dataUri = `data:text/plain;base64,${base64Content}`
+      const { filename, mimeType } = inferDocumentFileInfo(documentName)
+      const dataUri = `data:${mimeType};base64,${base64Content}`
 
-      // Parse document tags from various formats (object, array, JSON string)
       const parsedTags = parseDocumentTags(params.documentTags)
       const tagData = formatDocumentTagsForAPI(parsedTags)
 
       const documents = [
         {
-          filename: documentName.endsWith('.txt') ? documentName : `${documentName}.txt`,
+          filename,
           fileUrl: dataUri,
           fileSize: contentBytes,
-          mimeType: 'text/plain',
+          mimeType,
           ...tagData,
         },
       ]
diff --git a/apps/sim/tools/knowledge/types.ts b/apps/sim/tools/knowledge/types.ts
index 49fb6d8c33..3fa87ccaad 100644
--- a/apps/sim/tools/knowledge/types.ts
+++ b/apps/sim/tools/knowledge/types.ts
@@ -1,3 +1,38 @@
+import {
+  getFileExtension,
+  getMimeTypeFromExtension as getUploadMimeType,
+} from '@/lib/uploads/utils/file-utils'
+
+const TEXT_COMPATIBLE_MIME_TYPES = new Set([
+  'text/plain',
+  'text/html',
+  'text/markdown',
+  'text/csv',
+  'application/json',
+  'application/xml',
+  'application/x-yaml',
+])
+
+/**
+ * Extracts extension from a filename and returns the normalized filename and MIME type.
+ * If the extension maps to a recognized text-compatible MIME type, it is preserved.
+ * Otherwise, the filename is normalized to `.txt` with `text/plain`.
+ */
+export function inferDocumentFileInfo(documentName: string): {
+  filename: string
+  mimeType: string
+} {
+  const ext = getFileExtension(documentName)
+  if (ext) {
+    const mimeType = getUploadMimeType(ext)
+    if (TEXT_COMPATIBLE_MIME_TYPES.has(mimeType)) {
+      return { filename: documentName, mimeType }
+    }
+  }
+  const base = ext ? documentName.slice(0, documentName.lastIndexOf('.')) : documentName
+  return { filename: `${base || documentName}.txt`, mimeType: 'text/plain' }
+}
+
 export interface KnowledgeSearchResult {
   documentId: string
   documentName: string
diff --git a/apps/sim/tools/knowledge/upsert_document.ts b/apps/sim/tools/knowledge/upsert_document.ts
index 0314350a0d..5d1155f78a 100644
--- a/apps/sim/tools/knowledge/upsert_document.ts
+++ b/apps/sim/tools/knowledge/upsert_document.ts
@@ -1,6 +1,7 @@
-import type {
-  KnowledgeUpsertDocumentParams,
-  KnowledgeUpsertDocumentResponse,
+import {
+  inferDocumentFileInfo,
+  type KnowledgeUpsertDocumentParams,
+  type KnowledgeUpsertDocumentResponse,
 } from '@/tools/knowledge/types'
 import { enrichKBTagsSchema } from '@/tools/schema-enrichers'
 import { formatDocumentTagsForAPI, parseDocumentTags } from '@/tools/shared/tags'
@@ -94,18 +95,17 @@ export const knowledgeUpsertDocumentTool: ToolConfig<
         base64Content = btoa(binary)
       }
 
-      const dataUri = `data:text/plain;base64,${base64Content}`
+      const { filename, mimeType } = inferDocumentFileInfo(documentName)
+      const dataUri = `data:${mimeType};base64,${base64Content}`
 
       const parsedTags = parseDocumentTags(params.documentTags)
       const tagData = formatDocumentTagsForAPI(parsedTags)
 
-      const filename = documentName.endsWith('.txt') ? documentName : `${documentName}.txt`
-
       const requestBody: Record<string, unknown> = {
         filename,
         fileUrl: dataUri,
         fileSize: contentBytes,
-        mimeType: 'text/plain',
+        mimeType,
         ...tagData,
         processingOptions: {
           chunkSize: 1024,