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USQL MCP Server

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USQL MCP Server

License: MIT

usql-mcp is a full-featured MCP server that bridges the Model Context Protocol with the usql universal SQL CLI. It enables AI assistants and other MCP clients to query any database that usql supports, with enterprise-ready features like background execution, progress tracking, query safety validation, and intelligent caching.

✨ Key Features

  • 🔌 Universal Database Access: Query PostgreSQL, MySQL, Oracle, SQLite, SQL Server, and 100+ other databases through a single interface

  • ⚡ Background Execution: Long-running queries automatically move to background with job tracking and polling

  • 📊 Progress Reporting: Real-time progress updates for long operations using MCP progress notifications

  • 🛡️ Query Safety: Automatic risk analysis detects dangerous operations (DROP, DELETE without WHERE, etc.)

  • 📚 SQL Workflow Templates: Built-in prompts for common tasks (query optimization, data profiling, migrations)

  • 🗂️ Schema Resources: Browse database schemas through MCP resources (databases, tables, columns)

  • ⚡ Performance: Schema caching and rate limiting for production deployments

  • 🔒 Security: Credential sanitization, configurable operation blocking, audit-ready error messages

MCP Capabilities

This server implements all 4 MCP capabilities:

  1. Tools (8 tools): Execute queries, manage schemas, check job status

  2. Resources: Browse database metadata via sql:// URIs

  3. Prompts: SQL workflow templates for common tasks

  4. Progress: Real-time progress for long-running operations

Requirements

  • Node.js 16 or newer

  • npm

  • usql installed and available on PATH

Quick Launch with npx

Run the server directly via npx:

npx usql-mcp

This downloads the package and executes the CLI entry point, which runs the MCP server on stdio.

You can also run it directly from the repository using npm's Git support (the prepare script compiles the TypeScript automatically):

npx github:jvm/usql-mcp

Getting Started

git clone https://github.com/jvm/usql-mcp.git cd usql-mcp npm install npm run build

The compiled files live in dist/. They are intentionally not committed—run npm run build whenever you need fresh output.

Configuring Connections

Define connection strings via environment variables (USQL_*) or a config.json file mirroring config.example.json. Each USQL_<NAME>=... entry becomes a reusable connection whose name is the lower-cased <name> portion (USQL_ORACLE1 → oracle1).

Environment Variables

Connection variables (any USQL_* except reserved keys below):

export USQL_POSTGRES="postgres://user:password@localhost:5432/mydb" export USQL_SQLITE="sqlite:///$(pwd)/data/app.db" export USQL_ORACLE1="oracle://user:secret@host1:1521/service"

Reserved configuration variables:

  • USQL_CONFIG_PATH - Path to config.json

  • USQL_QUERY_TIMEOUT_MS - Default query timeout (leave unset for unlimited)

  • USQL_DEFAULT_CONNECTION - Default connection name when omitted from tool calls

  • USQL_BINARY_PATH - Full path to usql binary (if not on PATH)

  • USQL_BACKGROUND_THRESHOLD_MS - Threshold for background execution (default: 30000)

  • USQL_JOB_RESULT_TTL_MS - How long to keep completed job results (default: 3600000 = 1 hour)

Configuration File

Create a config.json with connection details and server settings:

{ "connections": { "postgres": { "uri": "postgres://user:password@localhost:5432/mydb", "description": "Production PostgreSQL database" }, "sqlite": { "uri": "sqlite:///path/to/database.db", "description": "Local SQLite database" } }, "defaults": { "defaultConnection": "postgres", "queryTimeout": null, "backgroundThresholdMs": 30000, "jobResultTtlMs": 3600000, "allowDestructiveOperations": true, "blockHighRiskQueries": false, "blockCriticalRiskQueries": false, "requireWhereClauseForDelete": false, "maxResultBytes": 10485760, "rateLimitRpm": null, "maxConcurrentRequests": 10, "schemaCacheTtl": null } }

Configuration Options:

  • queryTimeout: Milliseconds before query times out (null = unlimited)

  • backgroundThresholdMs: Queries exceeding this move to background (default: 30000)

  • jobResultTtlMs: How long to retain completed job results (default: 3600000)

  • allowDestructiveOperations: If false, block DROP/TRUNCATE operations

  • blockHighRiskQueries: Block queries with risk level "high"

  • blockCriticalRiskQueries: Block queries with risk level "critical"

  • requireWhereClauseForDelete: Require WHERE clause on DELETE/UPDATE

  • maxResultBytes: Maximum result size in bytes (default: 10MB)

  • rateLimitRpm: Requests per minute limit (null = no limit)

  • schemaCacheTtl: Schema cache TTL in milliseconds (null = no caching)

Client Configuration

This section explains how to configure the usql-mcp server in different MCP clients.

Claude Desktop

Claude Desktop uses a configuration file to register MCP servers. The location depends on your operating system:

  • macOS: ~/Library/Application Support/Claude/claude_desktop_config.json

  • Windows: %APPDATA%\Claude\claude_desktop_config.json

  • Linux: ~/.config/Claude/claude_desktop_config.json

Add the following configuration to your claude_desktop_config.json:

{ "mcpServers": { "usql": { "command": "npx", "args": ["-y", "usql-mcp"], "env": { "USQL_DEFAULT_CONNECTION": "oracle://user:secret@host:1521/service", "USQL_POSTGRES": "postgres://user:password@localhost:5432/mydb", "USQL_SQLITE": "sqlite:///path/to/database.db" } } } }

After editing the configuration file, restart Claude Desktop for changes to take effect.

Claude Code

Claude Code (CLI) supports MCP servers through its configuration file located at:

  • All platforms: ~/.clauderc or ~/.config/claude/config.json

Add the MCP server to your Claude Code configuration:

{ "mcpServers": { "usql": { "command": "npx", "args": ["-y", "usql-mcp"], "env": { "USQL_DEFAULT_CONNECTION": "oracle://user:secret@host:1521/service", "USQL_POSTGRES": "postgres://user:password@localhost:5432/mydb", "USQL_SQLITE": "sqlite:///path/to/database.db" } } } }

The server will be available in your Claude Code sessions automatically.

Codex CLI

Codex CLI configuration varies by implementation, but typically uses a similar JSON configuration approach. Create or edit your Codex configuration file (usually ~/.codexrc or as specified in your Codex documentation):

{ "mcp": { "servers": { "usql": { "command": "npx", "args": ["-y", "usql-mcp"], "env": { "USQL_DEFAULT_CONNECTION": "oracle://user:secret@host:1521/service", "USQL_POSTGRES": "postgres://user:password@localhost:5432/mydb", "USQL_SQLITE": "sqlite:///path/to/database.db" } } } } }

Refer to your specific Codex CLI documentation for the exact configuration file location and format.

GitHub Copilot (VS Code)

GitHub Copilot in VS Code can use MCP servers through the Copilot Chat extension settings. Configuration is done through VS Code's settings.json:

  1. Open VS Code Settings (JSON) via:

    • macOS: Cmd + Shift + P → "Preferences: Open User Settings (JSON)"

    • Windows/Linux: Ctrl + Shift + P → "Preferences: Open User Settings (JSON)"

  2. Add the MCP server configuration:

{ "github.copilot.chat.mcp.servers": { "usql": { "command": "npx", "args": ["-y", "usql-mcp"], "env": { "USQL_DEFAULT_CONNECTION": "oracle://user:secret@host:1521/service", "USQL_POSTGRES": "postgres://user:password@localhost:5432/mydb", "USQL_SQLITE": "sqlite:///path/to/database.db" } } } }

After saving the settings, reload VS Code or restart the Copilot extension for changes to take effect.

Environment Variables vs. Configuration

For all clients, you can choose between:

  1. Inline environment variables (shown above) - Connection strings in the config file

  2. System environment variables - Set USQL_* variables in your shell profile

System environment approach:

# In ~/.bashrc, ~/.zshrc, or equivalent export USQL_DEFAULT_CONNECTION="oracle://user:secret@host:1521/service" export USQL_POSTGRES="postgres://user:password@localhost:5432/mydb" export USQL_SQLITE="sqlite:///path/to/database.db"

Then use a simpler client configuration:

{ "mcpServers": { "usql": { "command": "npx", "args": ["-y", "usql-mcp"] } } }

Security Best Practices

  • Avoid hardcoding credentials: Use environment variables or secure credential stores

  • File permissions: Ensure configuration files with credentials are not world-readable (chmod 600)

  • Read-only access: Create database users with minimal required permissions for AI queries

  • Network security: Use SSL/TLS connections for remote databases

  • Audit logging: Enable database audit logs to track AI-generated queries

  • Query safety: Enable blockCriticalRiskQueries to prevent destructive operations

  • Rate limiting: Set rateLimitRpm to prevent abuse in multi-user environments

Tools Catalogue

Core SQL Tools

Tool

Purpose

Key Inputs

execute_query

Run an arbitrary SQL statement

connection_string, query, optional output_format (json|csv), timeout_ms

execute_script

Execute a multi-statement script

connection_string, script, optional output_format, timeout_ms

list_databases

List databases available on the server

connection_string, optional output_format, timeout_ms

list_tables

List tables in the current database

connection_string, optional output_format, timeout_ms

describe_table

Inspect table metadata via \d

connection_string, table, optional output_format, timeout_ms

Background Job Management

Tool

Purpose

Key Inputs

get_job_status

Check status of a background job

job_id, wait_seconds (1-55)

cancel_job

Cancel a running background job

job_id

Server Information

Tool

Purpose

Key Inputs

get_server_info

Get server configuration and stats

None (read-only)

Resources

Access database metadata through MCP resources:

  • sql://connections - List all available connections

  • sql://{connection}/databases - List databases on a connection

  • sql://{connection}/{database}/tables - List tables in a database

  • sql://{connection}/{database}/table/{name} - Get detailed table schema

Example usage:

Read resource: sql://postgres/production/tables Read resource: sql://postgres/production/table/users

Prompts

Built-in SQL workflow templates:

  1. analyze_performance - Analyze query performance and suggest optimizations

  2. profile_data_quality - Profile data quality (nulls, duplicates, distributions)

  3. generate_migration - Generate database migration scripts

  4. explain_schema - Create comprehensive schema documentation

  5. optimize_query - Optimize a slow-running query

  6. debug_slow_query - Systematically debug slow queries

Example usage:

Use prompt: analyze_performance connection: postgres query: SELECT * FROM large_table WHERE status = 'active'

Background Execution

Queries that exceed the backgroundThresholdMs (default: 30 seconds) automatically move to background execution:

  1. Initial Response: Tool returns a job_id and status message

  2. Polling: Use get_job_status with wait_seconds to check progress

  3. Results: When complete, get_job_status returns the full result

  4. Progress: Real-time progress percentage (0-100) for running jobs

  5. Cleanup: Jobs are automatically cleaned up after jobResultTtlMs (default: 1 hour)

Example workflow:

// Initial query (takes >30s) execute_query → { "status": "background", "job_id": "abc-123", "message": "Query is taking longer than 30000ms. Use get_job_status to check progress.", "started_at": "2025-01-15T10:30:00Z" } // Check status (waits up to 10s) get_job_status(job_id: "abc-123", wait_seconds: 10) → { "status": "running", "job_id": "abc-123", "progress": 45, // 45% complete "elapsed_ms": 15000 } // Eventually completes get_job_status(job_id: "abc-123", wait_seconds: 10) → { "status": "completed", "job_id": "abc-123", "result": { "format": "json", "content": "[...]" }, "elapsed_ms": 45000 }

Query Safety Analysis

Every query is automatically analyzed for safety risks:

Risk Levels:

  • Low: Safe read-only queries

  • Medium: Modifying operations with WHERE clauses

  • High: Complex queries with many JOINs, missing indexes

  • Critical: Destructive operations (DROP, TRUNCATE, DELETE without WHERE)

Response includes analysis:

{ "format": "json", "content": "[...]", "safety_analysis": { "risk_level": "critical", "warnings": ["DELETE operation without WHERE clause"], "dangerous_operations": ["DELETE"], "complexity_score": 2, "recommendations": ["Add WHERE clause to limit deletion scope"] } }

Configuration options:

  • allowDestructiveOperations: false - Block all destructive operations

  • blockHighRiskQueries: true - Block queries with "high" risk

  • blockCriticalRiskQueries: true - Block queries with "critical" risk

  • requireWhereClauseForDelete: true - Require WHERE on DELETE/UPDATE

Response Format

Successful calls return the exact stdout produced by usql, paired with the format indicator:

{ "format": "json", // or "csv" "content": "[{\"id\":1,\"name\":\"Alice\"}]", "elapsed_ms": 234, "safety_analysis": { "risk_level": "low", "warnings": [], "dangerous_operations": [], "complexity_score": 1, "recommendations": [] } }

Background job responses:

{ "status": "background", "job_id": "uuid-string", "message": "Query is taking longer than 30000ms. It will continue running in the background.", "started_at": "2025-01-15T10:30:00.000Z", "elapsed_ms": 30001 }

If usql exits with a non-zero code, the handler forwards the message through the MCP error shape, keeping details like the sanitized connection string and original stderr.

Performance Features

Schema Caching

Enable caching to reduce subprocess overhead for metadata queries:

{ "defaults": { "schemaCacheTtl": 300000 // 5 minutes } }

Cached operations:

  • list_databases

  • list_tables

  • describe_table

  • Resource reads

Cache statistics available via get_server_info:

{ "schema_cache_stats": { "hits": 42, "misses": 8, "size": 15, "hit_rate": 0.840 } }

Rate Limiting

Protect your databases from abuse:

{ "defaults": { "rateLimitRpm": 60, // 60 requests per minute "maxConcurrentRequests": 10 } }

When limit exceeded:

{ "error": "RateLimitExceeded", "message": "Rate limit exceeded: 60 requests per minute. Try again in 45 seconds.", "details": { "limit": 60, "current": 60, "resetInSeconds": 45 } }

Development

  • npm run dev – TypeScript compile in watch mode

  • npm run build – emit ESM output to dist/

  • npm run lint – ESLint/Prettier rules

  • npm run test – Jest unit tests (519 tests, comprehensive coverage)

  • npm run type-check – strict tsc --noEmit

Debug logging follows the namespace in DEBUG=usql-mcp:*.

Architecture

See CLAUDE.md for coding agents guidelines and architecture documentation.

Key components:

  • Tools (src/tools/) - MCP tool implementations

  • Resources (src/resources/) - MCP resource handlers

  • Prompts (src/prompts/) - SQL workflow templates

  • Background Jobs (src/usql/job-manager.ts) - Async execution tracking

  • Query Safety (src/utils/query-safety-analyzer.ts) - Risk analysis

  • Caching (src/cache/schema-cache.ts) - Performance optimization

  • Progress (src/notifications/progress-notifier.ts) - Real-time updates

Testing

# Run all tests npm test # Run specific test file npm test -- execute-query.test.ts # Run with coverage npm test -- --coverage # Integration tests (require usql installed) npm test -- integration

Test coverage:

  • 519 passing tests

  • Unit tests for all tools, utilities, and managers

  • Integration tests with real SQLite databases

  • Request tracking, pagination, and protocol compliance tests

Contributing

See CONTRIBUTING.md for contributor guidelines and CLAUDE.md for coding agents guidelines. Open an issue before large changes so we can keep the tooling lean and aligned with the MCP ecosystem.

License

MIT License - see LICENSE for details.

Credits

Built on top of the excellent usql universal database CLI by Kenneth Shaw and the Model Context Protocol by Anthropic.

Install Server
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security – no known vulnerabilities
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license - permissive license
A
quality - confirmed to work

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