jmd-mcp-sql 0.6.0

JMD-based MCP server for SQLite — natural language database interface

jmd-mcp-sql

MCP server that exposes a SQLite database through four JMD tools — a natural language database interface for LLM-driven workflows.

What is JMD?

JMD (JSON Markdown) is a lightweight document format that combines Markdown headings with key: value pairs. It is designed as a structured data format that LLMs can read and write naturally — without JSON brackets or SQL syntax. A heading line sets the document type and target table; the body carries the data:

# Order
id: 42
status: shipped
total: 149.99

A prefix on the heading selects the operation: # for data, #? for queries, #! for schema, #- for deletes. See the JMD specification for the full format definition.

Tools

Tool	# Data	#? Query	#! Schema	#- Delete
open	Open database / show status	—	—	—
read	SELECT by fields	SELECT with filters + aggregation	PRAGMA (describe table)	—
write	INSERT OR REPLACE	—	CREATE / ALTER TABLE	—
delete	—	—	DROP TABLE	DELETE WHERE

All inputs and outputs are JMD documents. The LLM speaks JMD — no SQL required.

Installation

Install from PyPI:

pip install jmd-mcp-sql

Or with uv (no manual install needed — uvx fetches it on demand):

uvx jmd-mcp-sql

Alternatively, install directly from GitHub:

pip install git+https://github.com/ostermeyer/jmd-mcp-sql.git

Configuration

The server runs as a stdio-based MCP server. Without arguments it starts with the bundled Northwind demo database. Pass a path to use your own SQLite file:

jmd-mcp-sql /path/to/your.db

The demo database ships as northwind.sql (plain text, version-controlled). On the first run without an explicit path, the server creates northwind.db from that dump automatically.

Claude Code

Add the server via CLI:

claude mcp add --transport stdio sql -- uvx jmd-mcp-sql

With a custom database:

claude mcp add --transport stdio sql -- uvx jmd-mcp-sql /path/to/your.db

This writes a .mcp.json in the project root (shareable via version control). You can also create it manually:

{
  "mcpServers": {
    "sql": {
      "command": "uvx",
      "args": ["jmd-mcp-sql"]
    }
  }
}

Claude Desktop / Cowork

Claude Cowork runs inside Claude Desktop. MCP servers configured in the Desktop config are automatically available in Cowork sessions.

Edit claude_desktop_config.json:

• macOS: ~/Library/Application Support/Claude/claude_desktop_config.json
• Windows: %APPDATA%\Claude\claude_desktop_config.json

{
  "mcpServers": {
    "sql": {
      "command": "uvx",
      "args": ["jmd-mcp-sql"]
    }
  }
}

With a custom database:

{
  "mcpServers": {
    "sql": {
      "command": "uvx",
      "args": ["jmd-mcp-sql", "/path/to/your.db"]
    }
  }
}

Restart Claude Desktop after saving the file. The server will appear as a tool in both Chat and Cowork mode.

VS Code

Create .vscode/mcp.json in the project root:

{
  "servers": {
    "sql": {
      "type": "stdio",
      "command": "uvx",
      "args": ["jmd-mcp-sql"]
    }
  }
}

Alternatively, add it to your VS Code settings.json (user or workspace):

{
  "mcp": {
    "servers": {
      "sql": {
        "type": "stdio",
        "command": "uvx",
        "args": ["jmd-mcp-sql"]
      }
    }
  }
}

JMD Document Syntax

Every document starts with a heading line that sets the document type and table name, followed by key: value pairs (one per line):

# Product          → data document   (exact lookup / insert-or-replace)
#? Product         → query document  (filter / list / aggregate)
#! Product         → schema document (describe / create / drop table)
#- Product         → delete document (delete matching records)

key: value         → string, integer, or float — inferred automatically
key: true/false    → boolean

Opening a Database

Open a different SQLite database at any time:

open("# Database\npath: /path/to/mydb.db")

If the file does not exist, a new empty database is created. The previous database is closed automatically. The response uses frontmatter for metadata and lists tables in the body:

path: /path/to/mydb.db
table-count: 3

# Database
## tables[]
- Customers
- Orders
- Products

Check which database is currently active:

open("# Database")

Path Restriction

The server reads optional settings from ~/.config/jmd/sql.jmd:

# Config
root: /Users/me/data

Field	Default	Description
root	(none)	Restricts open to databases under this directory tree

Without a config file, no restrictions apply and the server accepts any path.

Discovering the Database

To see which tables exist, read each table's schema:

read("#! Customers")

This returns a #! document with column names, JMD types, and modifiers (readonly = primary key, optional = nullable).

Typical Workflows

List all rows (small tables only):

read("#? Orders")

Filter rows — equality:

read("#? Orders\nstatus: shipped")

Filter rows — comparison:

read("#? Orders\nFreight: > 50")

Filter rows — alternation (OR):

read("#? Orders\nShipCountry: Germany|France|UK")

Filter rows — contains (case-insensitive substring):

read("#? Customers\nCompanyName: ~Corp")

Filter rows — regex pattern:

read("#? Products\nProductName: ^Chai.*")

Filter rows — negation (composes with any operator):

read("#? Orders\nShipCountry: !Germany")
read("#? Products\nProductName: !^LEGACY.*")

Look up one record:

read("# Customers\nid: 42")

Insert or replace a record:

write("# Orders\nid: 1\nstatus: pending\ntotal: 99.90")

Create a table:

write("#! Products\nid: integer readonly\nname: string\nprice: float optional")

Delete a record:

delete("#- Orders\nid: 1")

Drop a table:

delete("#! OldTable")

Pagination

Always use pagination when querying tables that may contain many rows.

Use frontmatter fields before the #? heading to control pagination:

read("page-size: 50\npage: 1\n\n#? Orders")

The response carries pagination metadata as frontmatter — before the root heading:

total: 830
page: 1
pages: 17
page-size: 50

# Orders
## data[]
- OrderID: 10248
  ...

Count only (no rows returned):

read("count: true\n\n#? Orders")

Returns:

count: 830

# Orders

Use total and pages to determine whether to fetch more pages. For tables with fewer than ~20 rows pagination is optional.

Field Projection

Use select: frontmatter to return only specific columns. This keeps responses small and context windows focused.

read("select: OrderID, EmployeeID\npage-size: 50\n\n#? Orders")

Works with both # (data) and #? (query) documents. When combined with aggregation, select: filters the result columns after the GROUP BY.

Joins

Use join: frontmatter to query across multiple tables in one call. The value is <TableName> on <JoinColumn> (INNER JOIN, equi-join on a column that exists in both tables).

read("join: Order Details on OrderID\nsum: UnitPrice * Quantity * (1 - Discount) as revenue\ngroup: EmployeeID\nsort: revenue desc\n\n#? Orders")

Multiple joins — comma-separated in a single join: value:

join: Order Details on OrderID, Employees on EmployeeID

Expression syntax — use <expression> as <alias> in aggregate functions to compute derived values across joined columns:

sum: UnitPrice * Quantity * (1 - Discount) as revenue

The alias becomes the result column name. Without as, the default alias <func>_<field> applies (e.g. sum_Freight).

Allowed in expressions: column names, numeric literals, arithmetic operators (+, -, *, /), and standard SQL functions (SUM, AVG, ROUND, …). Subqueries and SQL keywords are not permitted.

Projection rules for join queries:

• Unambiguous columns (appear in exactly one table) resolve automatically.
• Join key columns always resolve to the main table.
• Columns present in multiple tables (other than join keys) require explicit qualification — specify them via select: or filter on the unambiguous side.

Aggregation

Aggregation is expressed as frontmatter before the #? heading. QBE filter fields narrow rows before aggregation (SQL WHERE). The having: key filters after aggregation (SQL HAVING).

Key	SQL	Result column name
group: f1, f2	GROUP BY	grouping keys pass through unchanged
sum: field	SUM(field)	sum_field
avg: field	AVG(field)	avg_field
min: field	MIN(field)	min_field
max: field	MAX(field)	max_field
count	COUNT(*)	count

Multiple fields per function: sum: Freight, Total → sum_Freight and sum_Total.

Frontmatter	Meaning
sort: sum_revenue desc, EmployeeID asc	ORDER BY (multiple columns, mixed)
having: count > 5	HAVING COUNT(*) > 5
having: sum_Freight > 1000, count > 2	HAVING … AND … (comma = AND)

having: supports: >, >=, <, <=, =. sort: references any result column — grouping keys or aggregate aliases. page-size: and page: apply to the aggregated result set.

Example — top 3 employees by revenue:

read("group: EmployeeID\nsum: revenue\nsort: sum_revenue desc\npage-size: 3\n\n#? OrderDetails")

Error Handling

All tools return a # Error document on failure:

# Error
status: 400
code: not_found
message: No records found in Orders

Check the code field to decide how to proceed.

Specification

The JMD format is documented at jmd-spec.

License

MIT License. See LICENSE.