DB Explorer

Connect to databases, run queries, explore schemas, and export data — all from the terminal.

When to Use

Activate this skill when the user:
- Says "check the database", "query the DB", "show me the data"
- Wants to see table structure, row counts, or sample data
- Needs to export data to CSV/JSON
- Wants to find slow queries or check DB health
- Mentions a database connection string or DB name

Supported Databases

Quick Start

1. Identify the Database

Ask the user for:
- Database type (postgres/mysql/sqlite/mongo/redis)
- Connection string OR host/port/database/user/password
- For SQLite: just the file path

2. Connect and Explore

# PostgreSQL
psql "postgresql://user:password@host:5432/dbname" -c "\dt"           # list tables
psql "postgresql://user:password@host:5432/dbname" -c "\d table_name" # describe table
psql "postgresql://user:password@host:5432/dbname" -c "SELECT count(*) FROM table_name;"

# MySQL
mysql -h host -u user -p dbname -e "SHOW TABLES;"
mysql -h host -u user -p dbname -e "DESCRIBE table_name;"
mysql -h host -u user -p dbname -e "SELECT count(*) FROM table_name;"

# SQLite
sqlite3 /path/to/db.db ".tables"                    # list tables
sqlite3 /path/to/db.db ".schema table_name"         # describe table
sqlite3 /path/to/db.db "SELECT count(*) FROM table_name;"

# MongoDB
mongosh "mongodb://user:password@host:27017/dbname" --eval "db.getCollectionNames()"
mongosh "mongodb://user:password@host:27017/dbname" --eval "db.collection_name.countDocuments()"

# Redis
redis-cli -h host -p 6379 -a password INFO keyspace
redis-cli -h host -p 6379 -a password DBSIZE
redis-cli -h host -p 6379 -a password KEYS "*"

3. Safety Rules

ALWAYS follow these rules:

1. Read-only by default — Never run INSERT/UPDATE/DELETE/DROP without explicit user confirmation
2. Limit results — Always add LIMIT 100 (or equivalent) to SELECT queries unless user asks for all
3. Show before execute — For any write operation, show the exact SQL/command and ask for confirmation
4. No passwords in history — Use environment variables or connection strings, don't echo passwords
5. Transaction safety — For writes, wrap in BEGIN/ROLLBACK first, show results, then ask to COMMIT

4. Schema Exploration Workflow

When user says "explore the database" or "show me the schema":

# Step 1: List all tables
# Step 2: For each table, show columns, types, and constraints
# Step 3: Show row counts
# Step 4: Show foreign key relationships
# Step 5: Summarize as a readable schema map

PostgreSQL full schema dump:

psql "$CONN" -c "
SELECT table_name, column_name, data_type, is_nullable, column_default
FROM information_schema.columns
WHERE table_schema = 'public'
ORDER BY table_name, ordinal_position;
"

MySQL full schema dump:

mysql "$CONN" -e "
SELECT TABLE_NAME, COLUMN_NAME, DATA_TYPE, IS_NULLABLE, COLUMN_DEFAULT
FROM INFORMATION_SCHEMA.COLUMNS
WHERE TABLE_SCHEMA = DATABASE()
ORDER BY TABLE_NAME, ORDINAL_POSITION;
"

5. Export Formats

Export query results to common formats:

# CSV (PostgreSQL)
psql "$CONN" -c "\copy (SELECT * FROM table_name) TO '/tmp/export.csv' WITH CSV HEADER"

# CSV (MySQL)
mysql "$CONN" -e "SELECT * FROM table_name" | sed 's/\t/,/g' > /tmp/export.csv

# JSON (PostgreSQL)
psql "$CONN" -t -c "SELECT json_agg(t) FROM (SELECT * FROM table_name LIMIT 100) t;" > /tmp/export.json

# SQLite to CSV
sqlite3 /path/to/db.db ".mode csv" ".headers on" ".output /tmp/export.csv" "SELECT * FROM table_name;" ".quit"

6. Common Diagnostic Queries

-- PostgreSQL: Table sizes
SELECT schemaname, tablename, pg_size_pretty(pg_total_relation_size(schemaname||'.'||tablename))
FROM pg_tables WHERE schemaname = 'public' ORDER BY pg_total_relation_size(schemaname||'.'||tablename) DESC;

-- PostgreSQL: Active connections
SELECT pid, usename, application_name, client_addr, state, query_start, query
FROM pg_stat_activity WHERE state != 'idle';

-- PostgreSQL: Slow queries (> 1s)
SELECT pid, now() - pg_stat_activity.query_start AS duration, query
FROM pg_stat_activity WHERE state = 'active' AND now() - pg_stat_activity.query_start > interval '1 second';

-- MySQL: Table sizes
SELECT table_name, ROUND(data_length/1024/1024, 2) AS data_mb, table_rows
FROM information_schema.tables WHERE table_schema = DATABASE() ORDER BY data_length DESC;

-- MySQL: Process list
SHOW FULL PROCESSLIST;

Performance Analysis

PostgreSQL Performance

# Slow queries (active for > 1s)
psql "$CONN" -c "
SELECT pid, now() - query_start AS duration, query
FROM pg_stat_activity
WHERE state = 'active' AND now() - query_start > interval '1 second'
ORDER BY duration DESC;
"

# Index usage
psql "$CONN" -c "
SELECT schemaname, tablename, indexname, idx_scan, idx_tup_read
FROM pg_stat_user_indexes
ORDER BY idx_scan ASC LIMIT 20;
"

# Table bloat
psql "$CONN" -c "
SELECT schemaname, tablename,
  pg_size_pretty(pg_total_relation_size(schemaname||'.'||tablename)) AS total_size,
  pg_size_pretty(pg_relation_size(schemaname||'.'||tablename)) AS table_size,
  pg_size_pretty(pg_total_relation_size(schemaname||'.'||tablename) - pg_relation_size(schemaname||'.'||tablename)) AS index_size
FROM pg_tables
WHERE schemaname = 'public'
ORDER BY pg_total_relation_size(schemaname||'.'||tablename) DESC LIMIT 10;
"

# Cache hit ratio (should be > 99%)
psql "$CONN" -c "
SELECT
  sum(heap_blks_hit) / (sum(heap_blks_hit) + sum(heap_blks_read)) AS cache_hit_ratio
FROM pg_statio_user_tables;
"

MySQL Performance

# Slow queries
mysql "$CONN" -e "SELECT * FROM information_schema.processlist WHERE TIME > 1 ORDER BY TIME DESC;"

# Index usage
mysql "$CONN" -e "
SELECT table_name, index_name, cardinality
FROM information_schema.statistics
WHERE table_schema = DATABASE()
ORDER BY cardinality DESC LIMIT 20;
"

# Table sizes
mysql "$CONN" -e "
SELECT table_name,
  ROUND(data_length/1024/1024, 2) AS data_mb,
  ROUND(index_length/1024/1024, 2) AS index_mb,
  table_rows
FROM information_schema.tables
WHERE table_schema = DATABASE()
ORDER BY data_length DESC LIMIT 10;
"

Backup & Restore

PostgreSQL

# Backup single database
pg_dump "$CONN" > backup_$(date +%Y%m%d).sql

# Backup single table
pg_dump "$CONN" -t table_name > table_backup.sql

# Restore
psql "$CONN" < backup.sql

# Backup with compression
pg_dump "$CONN" | gzip > backup_$(date +%Y%m%d).sql.gz

MySQL

# Backup single database
mysqldump -h host -u user -p dbname > backup_$(date +%Y%m%d).sql

# Backup single table
mysqldump -h host -u user -p dbname table_name > table_backup.sql

# Restore
mysql -h host -u user -p dbname < backup.sql

SQLite

# Backup
sqlite3 /path/to/db.db ".backup /tmp/backup.db"

# Or just copy
cp /path/to/db.db /tmp/backup_$(date +%Y%m%d).db

Data Migration Helpers

Copy table between databases

# PostgreSQL to CSV to MySQL
psql "$PG_CONN" -c "\copy table_name TO '/tmp/export.csv' WITH CSV HEADER"
mysql "$MYSQL_CONN" -e "LOAD DATA LOCAL INFILE '/tmp/export.csv' INTO TABLE table_name FIELDS TERMINATED BY ',' ENCLOSED BY '\"' LINES TERMINATED BY '\n' IGNORE 1 ROWS;"

Schema comparison

# Get PostgreSQL schema hash for comparison
psql "$CONN" -c "
SELECT md5(string_agg(table_name || column_name || data_type, '' ORDER BY table_name, ordinal_position))
FROM information_schema.columns
WHERE table_schema = 'public';
"

Pitfalls

• Connection strings with special chars — URL-encode passwords containing @, :, /, etc.
• SSL requirements — Many cloud databases (RDS, Cloud SQL, Supabase) require ?sslmode=require or --ssl-mode=REQUIRED
• Timeout on large tables — Always LIMIT unless user explicitly wants full export
• SQLite locking — Only one writer at a time; use WAL mode for concurrent reads: PRAGMA journal_mode=WAL;
• MongoDB auth database — Sometimes auth is on admin db, not the target db: ?authSource=admin
• Redis SELECT — Redis has 16 databases (0-15); check which one: redis-cli INFO keyspace

Verification

After connecting:
1. Run a simple query to confirm connection works
2. List tables/collections to show the schema
3. Run a count query on a key table to verify data access
4. Check cache hit ratio (PostgreSQL) or slow queries (MySQL)
5. Verify backup capability with a test dump

Environment Variables

The skill uses these if available:
- DATABASE_URL — Full connection string (takes priority)
- DB_HOST, DB_PORT, DB_NAME, DB_USER, DB_PASSWORD — Individual params
- DB_TYPE — postgres/mysql/sqlite/mongo/redis