# Oscar for developers

Oscar keeps the books of Estonian companies. Your accountant runs the books
with Oscar, and you can reach your own data in two ways:

- **The API**, for your own code and integrations: read your invoices, your
  bank data and the reports, record and issue invoices, keep your parties, and
  upload documents.
- **The MCP server**, for an AI assistant such as Claude, ChatGPT or Cursor:
  connect it once, and it can answer questions about your books and do the
  same work for you, with the same permissions as you.

Both use the same API underneath, with the same permission checks. Neither
can do what only your accountant does: VAT returns, period closing and the
set-up of the books.

## Start with the API

1. Create an API key in the settings of your organization in the Oscar app.
   See [Authentication](/docs/api/guides/authentication).
2. Call `GET /api/organizations/` to find your organization, and
   `GET /api/organizations/{organization_id}/companies/` to find your
   companies. Then call any operation of the [API reference](/docs/api).
3. Read the guides before you write code that changes something:
   [Idempotency](/docs/api/guides/idempotency) and
   [Errors](/docs/api/guides/errors).

The public schema is at [`/docs/api/openapi.json`](/docs/api/openapi.json),
for a code generator or an API client.

## Start with an AI assistant

Read [Connect an AI assistant](/docs/mcp). The
[tool reference](/docs/mcp/tools) lists what the assistant can do.

## For AI agents

Every page of these docs is also Markdown: add `.md` to the address, for
example `/docs/api.md`. [`/llms.txt`](/llms.txt) lists every page, and
[`/llms-full.txt`](/llms-full.txt) holds all of them in one file.