document → fields → endpoint

Turn your document template into an API endpoint

Create invoices, contracts, and reports from your templates with one API call, or an MCP tool your agents can call.

MCP tool

{
  "name": "generate_invoice",
  "description": "Render an invoice PDF",
  "inputSchema": {
    "type": "object",
    "required": ["invoice_number", "due_date", "line_items"],
    "properties": {
      "invoice_number": { "type": "string" },
      "due_date": { "type": "string", "format": "date" },
      "line_items": { "type": "array" }
    }
  }
}

POST

/api/generate/gen_8kq2vn4r
content-type: application/json

{
  "invoice_number": "INV-0042",
  "due_date": "2026-07-12",
  "line_items": [
    { "description": "Design sprint", "qty": 12, "amount": 3000 },
    { "description": "Brand system", "qty": 1, "amount": 4800 }
  ]
}

InvoiceAcme Studio
hello@acme.studiofixed

Nº INV-0042Due Jul 12, 2026

Description	Qty	Amount
Design sprint	12	$3,000.00
Brand system	1	$4,800.00

Total$7,800.00

Authoring · the LLM runs here

find fieldsnatural-language editdocument

Runtime · no model, ever

validatemerge fixedrenderPDF

It finds the fields

When you create a generator, paperbrain reads the document: required fields, optional ones, and arrays that repeat per row. You never tag a variable by hand. A verifier then checks the inferred schema against the document’s actual placeholders, so if the model invents a field or misses one, you find out.

Fixed vs. variable, per field

Mark a field fixed (your company name, a standard rate) and it drops out of the API input entirely. This works inside array rows too: line_items[].unit_price can be a flat $250 on every line while quantity stays caller-supplied.

Draft never breaks Live

Publishing freezes the current version as the live input shape. After that you can keep editing and re-inferring all you want; callers and agents still hit exactly what you published. Every generation is logged with its merged input, so any document re-renders byte for byte later.

Agent-first

One document generator, callable two ways.

Every published generator exposes both a REST endpoint and a generate_<slug> MCP tool. Both accept the same JSON input, run the same validation, and render through the same deterministic pipeline.

{
  "name": "generate_invoice",
  "description": "Render an invoice PDF",
  "inputSchema": {
    "type": "object",
    "required": ["invoice_number", "line_items"],
    "properties": { … the same input fields … }
  }
}

Skip the blank page.

26 ready-made blueprints: invoices, offer letters, payslips, NDAs, packing slips, certificates. Browse the gallery →