SafeSelect MCP

Agents can look. They cannot mutate.

Fail-closed, read-only PostgreSQL and MongoDB access for AI coding agents over MCP.

SafeSelect gives coding agents a constrained database tool: discover structure, inspect production-shaped data, explain queries, diagnose connectivity, and recover stale connections without ever receiving write-capable tools or direct access to database credentials.

Most database MCP servers make it easy to connect an agent to a database. SafeSelect is built for the harder problem: letting an agent inspect production-shaped data without turning the database into an unrestricted tool surface.

[!NOTE] SafeSelect is a safety boundary for agent access, not a replacement for database permissions. Use least-privilege database users when you can; SafeSelect still constrains overpowered credentials when agents connect through it.

Current backend support: PostgreSQL and MongoDB.

Where It Helps

• Debug an application against realistic data without exposing mutation tools.
• Let an agent inspect schemas, indexes, query plans, and bounded rows during development.
• Explore MongoDB collections through bounded reads and sampled schema inference.
• Reuse existing DBeaver, Docker Compose, or MongoDB Compass connections.
• Give coding agents database context while keeping policy, limits, secrets, and audit under your control.

Why SafeSelect?

SafeSelect is intentionally narrower than general-purpose database MCP servers. It is not a tool builder, SQL workbench, or remote database gateway. It is a local safety boundary for agents that need database visibility, not database power.

What Makes It Different?

The product promise is simple: agents can look, but they cannot mutate. Even if the configured database user is a DBA, the agent still only receives SafeSelect's constrained read-only operations.

[!TIP] This is useful when teams already have DBeaver, Docker Compose, or MongoDB Compass connections and need to expose them to agents without redesigning database users first.

Backend Support

Architecture

The agent talks to SafeSelect through MCP stdio. SafeSelect enforces policy in Rust, stores secrets outside project files, and reaches databases through an embedded Java sidecar: JDBC for SQL backends and the MongoDB driver for MongoDB. The Rust to Java channel is JSON-lines over stdin/stdout: no sockets, no open ports.

Quick Start

brew install antonillos/tap/safeselect

# Import a project database
safeselect import-dbeaver ~/Downloads/dbeaver-export.zip
# or:
# safeselect import-compose
# safeselect import-compass --path "$HOME/.config/MongoDB Compass"

# Verify the environment
safeselect check --environment testing

# Install the MCP entry. If this is the only environment, its name is inferred.
safeselect agent install opencode

# Verify exactly what was installed and where.
safeselect agent status

SafeSelect uses any available Java 17+ runtime instead of requiring Homebrew's openjdk@17 formula specifically. If Java is missing or too old, install or select a Java 17+ runtime before running database commands.

The generated MCP name defaults to safeselect-<project>-<environment>.

The generated MCP entry is a stdio server scoped to one project and environment:

{
  "mcpServers": {
    "safeselect-myapp-testing": {
      "command": "safeselect",
      "args": ["serve", "--project", "/path/to/myapp", "--environment", "testing"]
    }
  }
}

SafeSelect uses each client's official MCP configuration contract, pins the absolute repository path, and defaults to user scope. Add --local for a project-scoped entry where the client supports it. See AI agent integration for exact paths, scopes, and manual configuration.

Agent Workflow

Agents should use SafeSelect in this order:

1. database_info
2. list_tables then describe_table; inspect list_table_indexes or bounded statistics when useful for SQL
3. list_databases, list_collections, then discover_document_schema for NoSQL
4. select / explain, or the bounded MongoDB read tool that matches the task
5. check, connect, or reconnect when connectivity is stale

Agents must discover relation or collection structure before querying unfamiliar data and use each discovery response's next_suggestion instead of guessing column or field names. SQL descriptions are catalog metadata; MongoDB schemas are inferred from a bounded, non-exhaustive sample.

MongoDB query documents must remain complete nested JSON values. Clients that flatten nested tool arguments can pass filter, projection, and sort as JSON-encoded object strings and pipeline as a JSON-encoded array string. redact_fields also accepts a JSON-encoded string array. Flattened keys are rejected so a lost filter or redaction can never become a less constrained fallback.

MongoDB server-side JavaScript is never available: $where, $function, and $accumulator are rejected recursively in filters, projections, sorts, and aggregation pipelines before the MongoDB driver receives them. When rejected, rebuild the request with declarative MQL operators; SafeSelect has no setting that enables JavaScript.

Query responses include row_count, byte_count, elapsed_ms, and a human-readable elapsed value so agents can reason about result size and latency.

Every MCP success and error includes one contextual next_suggestion. Agents should follow that single safe action, never blindly repeat an invalid request, and stop when the suggestion is terminal. For clients that only show an MCP error summary, SafeSelect also includes the trusted next suggestion in that summary without exposing database-derived detail.

Security Model

• Fail closed: security violations terminate the MCP process.
• Read only: SQL allows SELECT, EXPLAIN, and WITH; NoSQL backends allow discovery and read-only document reads.
• No server-side JavaScript: MongoDB $where, $function, and $accumulator are rejected in Rust and again in the Java sidecar.
• Scoped access: schemas, relations, databases, and collections can be allowed or denied.
• Hard limits: row count, result bytes, and timeouts are enforced; MongoDB read commands receive the same timeout as maxTimeMS.
• Secret isolation: passwords live in macOS Keychain or environment variables, never in project config.
• Driver verification: JDBC drivers are checked by SHA-256 before use.
• Audit trail: query text is hashed before being recorded; the current session exposes bounded audit metadata through audit_status and audit_recent.

Deliberate Limits

• SafeSelect does not expose database writes, migrations, administration, or arbitrary command execution.
• PostgreSQL and MongoDB are the supported backends today; broad connector count is not the goal.
• MCP transport is local stdio. SafeSelect is not a remote database gateway.
• MongoDB schema discovery is sampled and bounded, not an exhaustive schema guarantee.
• SafeSelect complements database-native least privilege; it does not replace it.

MCP Tools

When no .safeselect/ directory exists, safeselect serve --environment <env> enters setup mode automatically and exposes only the setup-safe tools.

[!IMPORTANT] Setup mode does not expose query tools. Agents can help import and validate configuration before any database inspection tools become available.

CLI Essentials

Use safeselect --help or a command-specific --help for the full CLI.

Uninstall checks both release-installer and Cargo binary locations. MongoDB Compass imports support SSH-tunneled mongodb+srv:// connections by resolving the SRV target and rewriting the local endpoint with the required TLS and direct-connection options.

Configuration

Global state lives in ~/.config/safeselect/ by default. Project policy lives in .safeselect/ at the repository root:

<repo-root>/
└── .safeselect/
    ├── project.toml
    └── environments/
        └── <env>.toml

SafeSelect walks upward from the current directory to find .safeselect/. Use --project <path> when an agent or script should target a specific repository.

Supported Agents

SafeSelect never silently falls back to a broader scope. In particular, --local for Windsurf fails with a clear correction because Windsurf does not document a project-scoped MCP configuration.

Build From Source

./install.sh
safeselect --version

Requirements: Rust 1.81+, Java 17+, Maven 3.8+. sshpass is optional for password-based SSH tunnels.

Documentation

• Installation guide
• AI agent integration
• Security model
• Security policy
• Distribution
• Changelog

Release notes are generated from CHANGELOG.md.

License

MIT - see LICENSE.