workbench-mcp

A local Python MCP server for interactive PostgreSQL data exploration, API integration, and automation on Fedora/Linux systems.

Overview

Version 1 includes:

• Python virtual environment setup for Fedora/Linux systems
• PostgreSQL 18 connectivity configured via .env file
• MCP tools for:
  • Discovering tables, columns, and schema structure
  • Running read-only query previews
  • Executing guarded SQL batches with temporary table support
  • Calling PostgreSQL stored functions and procedures
  • Accessing external APIs via full URL requests
  • Executing bash scripts available in PATH
• Enforced safety: persistent schema and data modifications are blocked
• Session-scoped temporary table workflows supported within SQL batches

Fedora / Linux Setup

Start by installing required system packages:

sudo dnf install -y python3 python3-pip nodejs npm

Python 3.12 or later is required. Use pyenv or similar if managing multiple versions.

Virtual Environment Setup

From the project root, create and activate a Python virtual environment:

python3 -m venv .venv
source .venv/bin/activate
python -m pip install --upgrade pip
pip install -e .

Environment Variables

Copy the example configuration and populate PostgreSQL connection details:

cp .env.example .env

Required:

• DB_HOST — PostgreSQL server hostname
• DB_NAME — Database name
• DB_USER — Database username
• DB_PASSWORD — Database password

Optional (tuning):

• DB_PORT — Connection port (default: 5432)
• DB_SSLMODE — SSL mode (default: prefer)
• DB_APPLICATION_NAME — Application identifier
• DB_QUERY_TIMEOUT_SECONDS — Query timeout (default: 30)
• DB_MAX_ROWS — Maximum rows per result set (default: 100)
• DB_MAX_RESULT_SETS — Maximum result sets per batch (default: 5)
• DB_OBJECT_PREVIEW_CHARS — Max definition preview length (default: 4000)

Example local development:

DB_HOST=localhost
DB_PORT=5432
DB_NAME=app_dev
DB_USER=app_user
DB_PASSWORD=your-secure-password
DB_SSLMODE=prefer

Optional: HTTP Request Tuning

The HTTP tool takes a full URL per call and does not require API profile configuration.

Supported environment settings:

Variable	Purpose
API_TIMEOUT_SECONDS	HTTP request timeout
API_MAX_RESPONSE_BYTES	Max response bytes returned by HTTP tools
API_VERIFY_SSL	true / false SSL verification (local dev certs)

Example call shape:

url: https://localhost:44331/api/breakouts/filter/1871161/dd-table?ParameterSetId=231022
method: GET

For authenticated calls, set API_BEARER_TOKEN in .env (or process env). HTTP tools automatically use it.

Run Locally

After activating the virtual environment and installing dependencies, start the MCP server with either command:

workbench-mcp

python -m workbench_mcp.server

MCP Inspector

For local MCP development and debugging, the MCP Inspector provides a fast manual test loop:

npx @modelcontextprotocol/inspector .venv/bin/python -m workbench_mcp.server

To launch the MCP server under debugpy for breakpoint debugging in the Inspector:

npx @modelcontextprotocol/inspector .venv/bin/python -m debugpy --listen 127.0.0.1:5678 -m workbench_mcp.server

After launch, open the Inspector UI, connect over STDIO, and test tools such as health, describe_object, and exec_proc_preview.

Breakpoints (debugpy): Use port 5678 for the debugger, not 6274 (6274 is only the Inspector web UI). Step-by-step workflow and “what was wrong before” are in docs/DEBUG_MCP.md.

VS Code Setup

To register the local MCP server in VS Code, add an entry to the workspace MCP configuration file:

• Workspace file: .vscode/mcp.json

Example configuration:

{
  "servers": {
    "workbench-mcp": {
      "type": "stdio",
      "command": "/absolute/path/to/workbench-mcp/.venv/bin/python",
      "args": ["-m", "workbench_mcp.server"]
    }
  }
}

Replace the command path with the local repository path to your virtual environment Python.

Secrets and Environment Values

You can supply environment values in either place:

1. workbench-mcp/.env
2. env in .vscode/mcp.json — VS Code injects these into the MCP server process.

Precedence: process environment (including .vscode/mcp.json → env) overrides values from .env for the same key.

Example with HTTP tuning in VS Code:

{
  "servers": {
    "workbench-mcp": {
      "type": "stdio",
      "command": "/absolute/path/to/workbench-mcp/.venv/bin/python",
      "args": ["-m", "workbench_mcp.server"],
      "env": {
        "API_TIMEOUT_SECONDS": "30",
        "API_MAX_RESPONSE_BYTES": "2097152",
        "API_VERIFY_SSL": "false"
      }
    }
  }
}

Do not commit real tokens. Prefer a local-only workspace configuration or omit env and use .env (which should stay out of git).

If other MCP servers are already configured, add workbench-mcp inside the existing servers object instead of replacing the entire file.

After saving .vscode/mcp.json, reload VS Code or refresh MCP servers so the new server is discovered. After the server loads, run the health tool before testing database procedures.

Initial Tools

• health
• describe_object
• list_tables_and_columns
• preview_query
• execute_readonly_sql
• exec_proc_preview
• exec_function_preview
• insert_row
• insert_rows
• http_get
• http_head
• http_post
• http_put
• http_patch
• http_delete
• execute_path_bash_script (script name resolved via PATH)

Safety Model

• Persistent DDL and DML are blocked in ad-hoc PostgreSQL batches
• Only temp-table writes are allowed, and only for temp tables created in the current batch
• preview_query allows only SELECT statements and CTE-based reads
• exec_proc_preview can execute PostgreSQL procedures and functions; overloaded routines should be passed with a signature such as public.my_func(integer, text)
• execute_path_bash_script only accepts script names (not paths), resolves them via PATH, and executes through bash

Suggested First Checks

After .env is configured, a typical validation flow is:

1. Describe the function, procedure, table, or view to inspect.
2. Preview the supporting configuration or reference data needed to understand that object.
3. Run exec_proc_preview, preview_query, or execute_readonly_sql with known inputs.
4. Compare the returned shape with the feature, investigation, or debugging scenario being evaluated.

Function Execution Example

For positional PostgreSQL function calls, use exec_function_preview. Pass PostgreSQL arrays as normal JSON lists.

Example SQL target:

select * from sales."Fn_GetSalesChamps"(2, 2025, array[1,2,5,6,7,8,9,10,11,12,15,16,18,19], 5);

Equivalent MCP tool input:

{
  "function_name": "sales.\"Fn_GetSalesChamps\"",
  "parameters": [2, 2025, [1, 2, 5, 6, 7, 8, 9, 10, 11, 12, 15, 16, 18, 19], 5]
}

Insert Examples

Single row insert:

{
  "table_name": "sales.orders",
  "row": {
    "customer_id": 10,
    "status": "new"
  },
  "returning_columns": ["order_id"]
}

Batch insert:

{
  "table_name": "sales.orders",
  "rows": [
    {"customer_id": 10, "status": "new"},
    {"customer_id": 11, "status": "pending"}
  ]
}