db2toon

A CLI tool that converts PostgreSQL database schemas into the Toon schema definition format.

Overview

db2toon connects to a database and extracts schema information (tables, columns, types, constraints, indexes, and comments), then converts it into the human-readable Toon format for database design documentation and visualization. PostgreSQL is currently supported; additional adapters can share the same schema model and encoder.

Features

• Schema Extraction: Automatically extracts tables, columns, and metadata from PostgreSQL
• Type Normalization: Simplifies PostgreSQL types (e.g., character varying → varchar)
• Relationship Mapping: Converts foreign key constraints to inline references or multi-column references
• Comment Preservation: Includes table and column comments in the output
• Index Documentation: Extracts and documents database indexes
• Cross-Platform: Builds without CGO for Linux, macOS, and Windows (amd64 and arm64)

Installation

From Source

git clone https://github.com/kamil5b/db2toon.git
cd db2toon
CGO_ENABLED=0 go build -o output/db2toon ./cmd/db2toon
CGO_ENABLED=0 go build -o output/pg2toon ./cmd/pg2toon

From Releases

Download pre-built binaries from the releases page for your platform.

Usage

LLM tool integration

Build and run the MCP-compatible stdio server:

CGO_ENABLED=0 go build -o output/db2toon-mcp ./cmd/db2toon-mcp
./output/db2toon-mcp

The server exposes db2toon.extract_schema. Its required arguments are dialect (postgres) and db; optional extraction settings are supplied in an options object. The tool is read-only, uses a 30-second default timeout, and limits responses to 4 MiB. Set options.timeout and options.max_output_bytes to lower limits when needed. Connection strings are never included in tool errors or results.

Basic Usage

./db2toon postgres -db "postgresql://user:password@localhost/dbname"

# Compatibility command; PostgreSQL is selected automatically.
./pg2toon -db "postgresql://user:password@localhost/dbname"

Save to File

./db2toon postgres -db "postgresql://user:password@localhost/dbname" -out schema.toon

Include up to two sample rows per table in the TOON output, using a stable ordering and a reproducible sample seed:

./db2toon postgres -db "postgresql://user:password@localhost/dbname" \
  -example-sample=2 -example-sample-ordered=true -seed=42

The default -example-sample=0 omits @example sections.

Select multiple schemas, include partitioned tables, and change the default 30-second operation timeout with:

./db2toon postgres -db "$DATABASE_URL" -schema audit
./db2toon postgres -db "$DATABASE_URL" -schemas public,audit -include-partitioned -timeout 1m

Flags

• -db string: Database connection URL (required)
• -out string: Output file path (optional, defaults to stdout)
• -schema string: A single schema to extract (defaults to public)
• -schemas string: Comma-separated schemas to extract; cannot be combined with -schema
• -include-partitioned: Include PostgreSQL partitioned tables
• -exclude-tables string: Comma-separated tables to exclude entirely; accepts table or schema.table
• -exclude-example-tables string: Comma-separated tables to exclude from @example sampling
• -exclude-example-fields string: Comma-separated qualified fields to exclude from examples, such as public.users.password_hash
• -example-sample int: Number of sample rows to include per table (defaults to 0)
• -example-sample-ordered: Select sample rows using deterministic ordering (defaults to false)
• -seed int: Seed for reproducible sample selection (defaults to 0)
• -timeout duration: Connection and extraction timeout (defaults to 30s)

Output Format

The Toon format provides a clean, human-readable schema definition:

[users]
# User accounts table

  id int {pk}
  email varchar {req}
  name varchar
  created_at timestamptz {req}

@indices
  idx_email: ON users USING btree (email)

@example[2]{id,email,name,created_at}:
  1,alice@example.com,Alice,2026-01-10T09:00:00Z
  2,bob@example.com,Bob,2026-01-11T10:30:00Z

[posts]
# Blog posts

  id int {pk}
  user_id int {req} -> users(id)
  title varchar {req}
  content text
  published_at timestamptz

[comments]
# Post comments

  id int {pk}
  post_id int {req} -> posts(id)
  user_id int {req} -> users(id)
  content text {req}
  created_at timestamptz {req}

Format Elements

• [TableName]: Table definition
• # comment: Table or column comments
• name type {tags}: Column definition with optional tags
  • {pk}: Primary key
  • {req}: Required (NOT NULL)
  • Multiple tags: {pk,req}
• -> table(column): Foreign key reference (inline for single columns)
• @indices: Section for database indexes
• @example[n]{columns}:: Up to n sampled rows from the table
• // comment: Inline column comment

Requirements

• Go 1.26.0 or later
• PostgreSQL 9.4+ (for JSON aggregation functions)
• Valid PostgreSQL connection string

License

MIT