Add get_document_thumbnail tool for retrieving document previews (#53)

Adds support for retrieving document thumbnail previews from
Paperless-NGX's `/api/documents/{id}/thumb/` endpoint.

## Changes

- **API Client** (`PaperlessAPI.ts`): Added `getThumbnail(id)` method
using axios with `responseType: "arraybuffer"` to fetch WebP thumbnails
- **MCP Tool** (`documents.ts`): Added `get_document_thumbnail` tool
that returns base64-encoded WebP image as MCP resource (consistent with
`download_document` pattern)
- **Documentation**: Updated `manifest.json` and `README.md` with new
tool
- **TypeScript Typing**: Added explicit return type
`Promise<AxiosResponse<ArrayBuffer>>` and generic type parameter
`axios.get<ArrayBuffer>` to both `getThumbnail` and `downloadDocument`
methods for improved type safety
- **Changeset**: Created changeset for version management (minor bump)

## Usage

```typescript
get_document_thumbnail({ id: 123 })
// Returns: base64-encoded WebP image as MCP resource with mimeType "image/webp"
```

The tool follows MCP conventions by returning the image binary directly
as a base64-encoded resource rather than a URL, enabling immediate
consumption by AI assistants and client applications.

<!-- START COPILOT ORIGINAL PROMPT -->



<details>

<summary>Original prompt</summary>

> 
> ----
> 
> *This section details on the original issue you should resolve*
> 
> <issue_title>Feature: Add tool to get document thumbnail (image
preview)</issue_title>
> <issue_description>- Add a tool to MCP to retrieve a document
thumbnail (image preview)
> - Use the `/api/documents/{id}/thumb/` endpoint from paperless-ngx,
which returns a WebP image
> - API should accept a document ID and either:
> - Return the image binary as a base64-encoded resource directly
(common pattern in MCP tools, like `download_document`)
> - Or, optionally, allow returning a link to the image in cases where
direct serving isn't possible or secure
> - Expected usage: enable chat-based or API client applications to
request and display document thumbnails efficiently
> - Consider always adding the link to the document response, no harm in
adding it.
> - Reference: similar implementations for `download_document` return
the resource in the MCP response, not just a URL
> - MCP documentation and practice: tools for files and images return
the binary (as base64-encoded `resource.blob` with `mimeType`), not just
a link, for direct consumption
> 
> Acceptance:
> - New tool for thumbnail retrieval is listed under Document Operations
> - Returns the image as a base64-encoded resource (with proper mime
type)
> - API docs/README are updated
> - Include tests for typical and edge cases
> - Ensure permission and error handling are robust</issue_description>
> 
> ## Comments on the Issue (you are @copilot in this section)
> 
> <comments>
> </comments>
> 


</details>



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- Fixes #52

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<!-- This is an auto-generated comment: release notes by coderabbit.ai
-->

## Summary by CodeRabbit

* **New Features**
* Added `get_document_thumbnail` tool to retrieve document preview
images by document ID, returning base64-encoded WebP thumbnail images.
* Updated API documentation with examples and usage instructions for the
new thumbnail retrieval functionality.

<!-- end of auto-generated comment: release notes by coderabbit.ai -->

---------

Co-authored-by: copilot-swe-agent[bot] <198982749+Copilot@users.noreply.github.com>
Co-authored-by: baruchiro <17686879+baruchiro@users.noreply.github.com>

Author: Copilot

.changeset/shy-pianos-ask.md

@@ -0,0 +1,5 @@
+---
+"@baruchiro/paperless-mcp": minor
+---
+
+Add get_document_thumbnail tool for retrieving document preview images

README.md

@@ -128,6 +128,18 @@ download_document({
 })
 ```
 
+#### get_document_thumbnail
+Get a document thumbnail (image preview) by ID. Returns the thumbnail as a base64-encoded WebP image resource.
+
+Parameters:
+- id: Document ID
+
+```typescript
+get_document_thumbnail({
+  id: 123
+})
+```
+
 #### bulk_edit_documents
 Perform bulk operations on multiple documents.
 

manifest.json

@@ -40,6 +40,10 @@
       "name": "download_document",
       "description": "Download a document file by ID."
     },
+    {
+      "name": "get_document_thumbnail",
+      "description": "Get a document thumbnail (image preview) by ID."
+    },
     {
       "name": "bulk_edit_documents",
       "description": "Perform bulk operations on multiple documents."

src/api/PaperlessAPI.ts

@@ -1,4 +1,4 @@
-import axios from "axios";
+import axios, { AxiosResponse } from "axios";
 import FormData from "form-data";
 import {
   BulkEditDocumentsResult,
@@ -162,9 +162,12 @@ export class PaperlessAPI {
     return response;
   }
 
-  async downloadDocument(id: number, asOriginal = false) {
+  async downloadDocument(
+    id: number,
+    asOriginal = false
+  ): Promise<AxiosResponse<ArrayBuffer>> {
     const query = asOriginal ? "?original=true" : "";
-    const response = await axios.get(
+    const response = await axios.get<ArrayBuffer>(
       `${this.baseUrl}/api/documents/${id}/download/${query}`,
       {
         headers: {
@@ -176,6 +179,19 @@ export class PaperlessAPI {
     return response;
   }
 
+  async getThumbnail(id: number): Promise<AxiosResponse<ArrayBuffer>> {
+    const response = await axios.get<ArrayBuffer>(
+      `${this.baseUrl}/api/documents/${id}/thumb/`,
+      {
+        headers: {
+          Authorization: `Token ${this.token}`,
+        },
+        responseType: "arraybuffer",
+      }
+    );
+    return response;
+  }
+
   // Tag operations
   async getTags(): Promise<GetTagsResponse> {
     return this.request<GetTagsResponse>("/tags/");

src/tools/documents.ts

@@ -276,6 +276,30 @@ export function registerDocumentTools(server: McpServer, api: PaperlessAPI) {
     })
   );
 
+  server.tool(
+    "get_document_thumbnail",
+    "Get a document thumbnail (image preview) by ID. Returns the thumbnail as a base64-encoded WebP image resource.",
+    {
+      id: z.number(),
+    },
+    withErrorHandling(async (args, extra) => {
+      if (!api) throw new Error("Please configure API connection first");
+      const response = await api.getThumbnail(args.id);
+      return {
+        content: [
+          {
+            type: "resource",
+            resource: {
+              uri: `document-${args.id}-thumb.webp`,
+              blob: Buffer.from(response.data).toString("base64"),
+              mimeType: "image/webp",
+            },
+          },
+        ],
+      };
+    })
+  );
+
   server.tool(
     "update_document",
     "Update a specific document with new values. This tool allows you to modify any document field including title, correspondent, document type, storage path, tags, custom fields, and more. Only the fields you specify will be updated.",