Prerequisites

• I've searched the current open issues
• I've updated to the latest version of Toolbox

Toolbox version

latest as of 7/9/25

Environment

Toolbox Source: https://github.com/googleapis/genai-toolbox (commit 72a7282)
Built from source on 2025-07-09
Docker Engine: 24.0.7, macOS 14.5, M1 chip
Database: MySQL 8.0, containerized
Command: /toolbox toolbox --tools-file /app/tools.yaml --address 0.0.0.0 --port 8080

Client

MCP Inspector (Community Tool)
Latest version as of 2025-07-09 (installed via npm)
URL: http://localhost:8888/mcp
Transport: streamable-http

Expected Behavior

I expected the MCP Toolbox server to return string fields such as store, date, and total_amount as plain, human-readable text (e.g., "Trader Joe's", "2025-05-25", "148.23"), matching the output of direct SQL queries to the underlying MySQL database using JSON_UNQUOTE.

Current Behavior

All string fields in the MCP Toolbox response are returned as base64-encoded values (e.g., "VHJhZGVyIEpvZSdz" instead of "Trader Joe's"). This occurs for all tools that query these fields, even though direct SQL queries to the database return standard string values. This unexpected encoding makes the output difficult to use with clients and downstream tools, and does not match the behavior described in the documentation.

{
type:
"text"
text:
"{"date":"MjAyNS0wNS0yNg==","item_count":32,"receipt_id":20,"store":"VHJhZGVyIEpvZSdz","total_amount"..."
}

Steps to reproduce?

1. Set up a minimal MySQL 8 container with a database and user.
2. Create a receipts table with a JSON column and insert test data:

CREATE TABLE receipts (
  receipt_id INT PRIMARY KEY AUTO_INCREMENT,
  storeName JSON,
  status VARCHAR(20)
);

INSERT INTO receipts (storeName, status)
VALUES ('{"verified": "Whole Foods"}', 'verified');

3. Create a minimal tools-test.yaml for MCP Toolbox:

sources:
  test-mysql:
    kind: mysql
    host: mysql-test
    port: 3306
    database: testdb
    user: testuser
    password: testpass

tools:
  filter-test-receipts:
    kind: mysql-sql
    source: test-mysql
    description: Filter test receipts
    statement: |
      SELECT * FROM receipts
    parameters: []

toolsets:
  default:
    - filter-test-receipts

4. Start MCP Toolbox with config to connect to the MySQL and tools-test.yaml
5. Query the MCP server using MCP Inspector or HTTP POST

{
  "tool": "filter-test-receipts",
  "params": {}
}

6. Observe the output - The value for storeName in the response will be base64-encoded, e.g.

"storeName": "eyJ2ZXJpZmllZCI6ICJXaG9sZSBGb29kcyJ9"

Decoding this gives the expected JSON: {"verified": "Whole Foods"}

Additional Details

Values stored in DB are NOT base64 encoded