> ## Documentation Index
> Fetch the complete documentation index at: https://docs.modusbrain.com/llms.txt
> Use this file to discover all available pages before exploring further.

# Environment variables

> MODUSBRAIN_* configuration with MODUSBRAIN_* legacy aliases.

# Environment variables

ModusBrain prefers `MODUSBRAIN_*` environment variables. Legacy `MODUSBRAIN_*` names still work.

## Home and config

| Variable          | Description                                          |
| ----------------- | ---------------------------------------------------- |
| `MODUSBRAIN_HOME` | Parent directory for config (appends `/.modusbrain`) |
| `GBRAIN_HOME`     | Legacy alias for `MODUSBRAIN_HOME`                   |

## Database

| Variable                  | Description             |
| ------------------------- | ----------------------- |
| `MODUSBRAIN_DATABASE_URL` | Postgres connection URL |
| `GBRAIN_DATABASE_URL`     | Legacy alias            |

## Source routing

| Variable            | Description                   |
| ------------------- | ----------------------------- |
| `MODUSBRAIN_SOURCE` | Default source ID for CLI/MCP |
| `GBRAIN_SOURCE`     | Legacy alias                  |

Dotfile: `.modusbrain-source` (legacy `.gbrain-source` also read)

## Models and API keys

| Variable                     | Description                        |
| ---------------------------- | ---------------------------------- |
| `ANTHROPIC_API_KEY`          | For synthesis (`modusbrain think`) |
| `OPENAI_API_KEY`             | Embeddings (optional)              |
| `MODUSBRAIN_EMBEDDING_MODEL` | Override embedding model           |
| `MODUSBRAIN_CHAT_MODEL`      | Override chat model                |

## Example

```bash theme={null}
export MODUSBRAIN_HOME=$HOME
export MODUSBRAIN_SOURCE=default
modusbrain doctor
```