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Config file location

~/Library/Application Support/Claude/claude_desktop_config.json

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Minimal configuration

Add Isthmus to the mcpServers object: 
{
  "mcpServers": {
    "isthmus": {
      "command": "isthmus",
      "env": {
        "DATABASE_URL": "postgres://user:password@localhost:5432/mydb"
      }
    }
  }
}

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Full configuration

Include optional settings for schema filtering, policy enrichment, and row limits: 
{
  "mcpServers": {
    "isthmus": {
      "command": "isthmus",
      "args": ["--audit-log", "/tmp/isthmus-audit.ndjson"],
      "env": {
        "DATABASE_URL": "postgres://user:password@localhost:5432/mydb",
        "SCHEMAS": "public,analytics",
        "POLICY_FILE": "/path/to/policy.yaml",
        "MAX_ROWS": "500"
      }
    }
  }
}

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Verify

  1. Save the config file
  2. Restart Claude Desktop (Cmd+Q, then reopen)
  3. Look for the MCP tools icon in the chat input area
  4. Ask: “What tables are in my database?”
Claude should call discover and return a summary of your database.

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Troubleshooting

Claude Desktop needs isthmus in your PATH. Check where it’s installed:
which isthmus
If it’s not in your PATH, use the full path in the config. The location depends on how you installed:
  • Install script / prebuilt binary: /usr/local/bin/isthmus
  • go install: ~/go/bin/isthmus
"command": "/usr/local/bin/isthmus"
On macOS, the config file must be at exactly:
~/Library/Application Support/Claude/claude_desktop_config.json
Create the file if it doesn’t exist. Make sure it’s valid JSON.
Test connectivity outside Claude Desktop first:
DATABASE_URL="postgres://user:password@localhost:5432/mydb" isthmus --dry-run
If this fails, check your connection string, network, and Postgres status.