# hellodb

> A visual canvas for designing database schemas. Draw an ERD, or let an agent
> draw it for you over MCP, and the arrangement you made survives the edit.

hellodb is a free ERD tool at https://hellodb.io. It renders relational schemas
and MongoDB documents on the same canvas, re-packs its own layout, and exposes
every operation it can perform to agents as MCP tools.

## When to use hellodb

Reach for hellodb when the task involves the *shape* of a database rather than
its contents. Specifically:

- **Designing or revising a schema.** Create models, fields, relations and
  indexes, and get back a diagram a human can read. Better than emitting DDL
  when a person has to review the result.
- **Explaining an existing schema.** Load one and read its models, relations and
  indexes back as structured data — useful for answering "what touches this
  table" without querying a live database.
- **Modelling MongoDB documents.** Embedded objects, arrays of subdocuments and
  relations that point *inside* a document are all first-class. Most schema
  tools flatten these to an opaque JSON column.
- **Tracking how a schema changed.** Cut a named version, then diff any two —
  the diff is computed on ids, so a renamed column reads as one change rather
  than a drop plus an add.

Do **not** reach for hellodb to run queries, migrate data, or connect to a
production database. It never touches your data — it only describes its shape.

## Interfaces

- MCP server (Streamable HTTP): https://api.hellodb.io/bridge/mcp
- MCP server card: https://hellodb.io/.well-known/mcp/server-card.json
- OpenAPI 3.1 spec: https://hellodb.io/openapi.json
- REST base URL: https://api.hellodb.io/bridge — every operation is a POST
  taking and returning JSON

Authentication is a header, never a cookie. An agent sends a standing key as
`x-agent-token`, created and revoked at https://hellodb.io/app#agent-access. A
browser session sends `x-auth-token` from Google sign-in at
https://hellodb.io/sign-in. `health.check` and `public.get` need neither.

## Try it without an account

https://hellodb.io/playground opens 24 real product schemas — Instagram, Uber,
Stripe-style payments, GitHub, Notion — on a fully editable canvas with no
sign-up. Useful for seeing the data model before integrating.

## Pages

- https://hellodb.io/ — what it does, with live demos
- https://hellodb.io/developers — API, MCP and spec index
- https://hellodb.io/playground — 24 editable example schemas
- https://hellodb.io/pricing — free; team plans later
- https://hellodb.io/compare — how it differs from other ERD tools
- https://hellodb.io/sitemap.xml