▣ OUTPUT KIT

Validate & Generate Documents from Templates

What it does

The Document Template API fills DOCX, HTML and Markdown templates with JSON data. Send a template and the values it reads, and get back a finished DOCX, PDF or HTML document. A separate endpoint checks DOCX templates before you use them.

To check a template, send it to the validate endpoint with your data. It tells you if the template is valid. It also lists the variables it reads, keys missing from your data, keys it never uses, and syntax errors with line numbers.

To fill a Word template, send it as template_base64 with data. Set format to json (default), docx or pdf. To fill an HTML or Markdown template, send template with data. Add css, a title and page settings, and set markdown to false for plain HTML. format takes pdf (default), html or json. On both endpoints, download set to true returns the file itself. Otherwise you get a data_uri with the bytes, media_type, warnings and timing.

Teams use the Document Template API to fill Word templates for contracts and proposals. Others generate invoices and customer letters in their own design, or export reports to PDF from HTML templates.

For fixed layouts that need no template, use the Generate Invoice Document from JSON API or the Generate Report Document from JSON API.

▣ ENDPOINT 01 / 03

POST

Validate a DOCX template

https://api.eu.apyhub.com/callable-labs/validate-generate-documents-from-templates/v1/documents/validate

QUICKSTART

GUIDE

Quickstart

Validate a .docx template by uploading the template file and, optionally, a JSON string of template data.

curl -X POST "https://api.eu.apyhub.com/callable-labs/validate-generate-documents-from-templates/v1/documents/validate" \
  -H "apy-token: $APY_TOKEN" \
  -F "template=@/path/to/template.docx" \
  -F 'data={"name":"Ava","company":"ApyHub"}'

What you'll get back

Returns a JSON object with these top-level fields: ok boolean, engine string, unused array of strings, undefined array of strings, variables array of strings, and syntax_errors array of objects. ok is false when the template has syntax errors.

{
  "ok": true,
  "engine": "docxtemplater",
  "unused": [],
  "undefined": [],
  "variables": ["name", "company"],
  "syntax_errors": []
}

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API key

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Max 100MB total per request (all files combined). Larger? Use this API's URL-based endpoint instead, if it has one.

About this endpoint

What it does

Validates a .docx template and checks it against optional input data. It returns whether the template parsed successfully, plus details about template variables, unused input keys, undefined variables, and any syntax errors.

Request Body

Parameter	Type	Description
template	String	The `.docx` template to inspect.
data	String	Optional JSON object to check against the template's variables. Can be `null`.

Response

Returns a JSON object with ok as a boolean field, engine as a string field, unused, undefined, and variables as string array fields, and syntax_errors as an array field of objects containing line as an integer and message as a string. ok is false when the template has syntax errors.

Parameter	Type	Description
ok	Boolean	`false` when the template has syntax errors.
engine	String	Template engine name.
unused	String Array	Keys of `data` no tag reads.
undefined	String Array	Variables `data` does not provide.
variables	String Array	Top-level names the template reads.
syntax_errors	Object Array	Syntax errors found in the template, as objects with `line` and `message` fields.

Notes

The request body is unwrapped from the parser’s internal body envelope, so callers should send template and data as top-level body fields, not nested under a body object.

Max 100MB total per request (all files combined). Larger? Use this API's URL-based endpoint instead, if it has one.

▣ ENDPOINT 02 / 03

POST

Fill a DOCX template

https://api.eu.apyhub.com/callable-labs/validate-generate-documents-from-templates/v1/documents/render

QUICKSTART

GUIDE

Quickstart

Render a DOCX template from base64 and return the rendered result in the default JSON format.

curl -X POST "https://api.eu.apyhub.com/callable-labs/validate-generate-documents-from-templates/v1/documents/render" \
  -H "apy-token: $APY_TOKEN" \
  -H "Content-Type: application/json" \
  -d '{
    "template_base64": "UEsDBBQAAAAIA...",
    "data": {
      "customer": { "name": "Ada Lovelace" },
      "items": [
        { "name": "Widget", "qty": 2, "price": 9.5 }
      ]
    }
  }'

What you'll get back

Returns a JSON object with rendering metadata such as bytes (integer), cache ("hit" or "miss"), pages (integer or null), engine (string), format ("docx", "pdf", or "html"), data_uri (string), warnings (array of strings), queued_ms (integer), render_ms (integer), media_type (string), and engine_version (string).

{
  "bytes": 12345,
  "cache": "miss",
  "pages": null,
  "engine": "libreoffice",
  "format": "docx",
  "data_uri": "data:application/vnd.openxmlformats-officedocument.wordprocessingml.document;base64,...",
  "warnings": [],
  "queued_ms": 12,
  "render_ms": 45,
  "media_type": "application/vnd.openxmlformats-officedocument.wordprocessingml.document",
  "engine_version": "7.6.0"
}

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API key

Loading your default key…

The full key is used to call the gateway and stays in this tab — never sent to orbit or saved.

About this endpoint

What it does

Fills a DOCX template using the values you provide in the request body. The endpoint can return the rendered file as DOCX or PDF, or as a JSON response containing a base64 data URI and metadata.

Request Body

Parameter	Type	Description
data	Object	The values the template reads, as a JSON object. Every variable the template references must be present or the response will contain `data_error`. For DOCX templates, a value shaped `{"$image": "<base64 PNG/JPEG>", "width_mm": 40}` is inserted as a picture. Supports up to 256 KiB and up to 20 levels deep.
format	ENUM	Output format. Allowed values: `json` (default), `docx`, `pdf`. `docx` returns the filled document. `pdf` converts the document with LibreOffice. `json` returns the DOCX as a base64 data URI plus metadata.
download	Boolean	When `true`, sends `Content-Disposition: attachment` so browsers save the file. Default: `false`.
template_base64	String	The `.docx` template, base64-encoded. Maximum decoded size: 5 MiB.

Response

Returns a JSON object with metadata about the rendered output. The object includes bytes (integer), cache (string), pages (integer, nullable), engine (string), format (string), data_uri (string), warnings (array of strings), queued_ms (integer), render_ms (integer), media_type (string), and engine_version (string).

Parameter	Type	Description
bytes	Integer	Size of the rendered output in bytes.
cache	ENUM	Cache result. Allowed values: `hit`, `miss`.
pages	Integer	PDF page count. `null` for DOCX/HTML.
engine	String	Rendering engine used.
format	ENUM	Output format. Allowed values: `docx`, `pdf`, `html`.
data_uri	String	`data:<media_type>;base64,…` representation of the rendered output.
warnings	Object Array	Warnings produced during rendering. The schema defines this as an array of strings.
queued_ms	Integer	Time spent queued, in milliseconds.
render_ms	Integer	Time spent rendering, in milliseconds.
media_type	String	Media type of the rendered output.
engine_version	String	Version of the rendering engine.

▣ ENDPOINT 03 / 03

POST

Render an HTML or Markdown template

https://api.eu.apyhub.com/callable-labs/validate-generate-documents-from-templates/v1/documents/html

QUICKSTART

GUIDE

Quickstart

Render a simple HTML template with the minimum required input.

curl -X POST "https://api.eu.apyhub.com/callable-labs/validate-generate-documents-from-templates/v1/documents/html" \
  -H "apy-token: $APY_TOKEN" \
  -H "Content-Type: application/json" \
  -d '{
    "template": "<h1>Hello {{ name }}</h1>",
    "data": {
      "name": "Ada"
    }
  }'

What you'll get back

Returns a JSON object with rendering metadata. Top-level fields include bytes (integer), cache (hit or miss), pages (integer or null), engine (string), format (docx, pdf, or html), data_uri (string), warnings (array of strings), queued_ms (integer), render_ms (integer), media_type (string), and engine_version (string).

{
  "bytes": 1234,
  "cache": "miss",
  "pages": null,
  "engine": "render-html-template",
  "format": "html",
  "data_uri": "data:text/html;base64,PGgxPkhlbGxvIEFkYTwvaDE+",
  "warnings": [],
  "queued_ms": 12,
  "render_ms": 34,
  "media_type": "text/html",
  "engine_version": "1.0.0"
}

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API key

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HtmlRequest*

HTML or Markdown template + data → HTML or PDF.

Template*

Jinja2 template in HTML or Markdown (≤ 256 KiB). Values are HTML-escaped; use `{{ value | safe }}` to insert markup on purpose. A fragment is wrapped in a document shell with consistent fonts; a full `<html>` document is printed as-is.

Css

Extra stylesheet appended to the document shell. External URLs are never fetched.

Data

The values the template reads, as a JSON object (≤ 256 KiB, ≤ 20 levels deep). Every variable the template references must be present (`data_error` otherwise). For DOCX templates a value shaped `{"$image": "<base64 PNG/JPEG>", "width_mm": 40}` is inserted as a picture.

name

PageOptions

Paper size and margins for PDF output.

Size

Paper size.

About this endpoint

What it does

Renders a Jinja2 template from template using the values in data, with optional styling and page settings. Depending on format, it returns either the rendered HTML as a data URI with metadata, or the rendered file bytes for HTML/PDF output.

Request Body

Parameter	Type	Description
css	String	Extra stylesheet appended to the document shell. External URLs are never fetched.
data	Object	The values the template reads, as a JSON object (≤ 256 KiB, ≤ 20 levels deep). Every variable the template references must be present (`data_error` otherwise). For DOCX templates a value shaped `{"$image":"<base64 PNG/JPEG>","width_mm":40}` is inserted as a picture.
page	Object	Paper size and margins for PDF output. Contains `size`, `margin_mm`, and `orientation`.
page.size	ENUM	Paper size. Allowed values: `A4`, `Letter`, `Legal`, `A3`, `A5`. Default: `A4`.
page.margin_mm	Number	Uniform page margin in millimetres. Default: `18`. Minimum: `0`. Maximum: `50`.
page.orientation	ENUM	Default: `portrait`. Allowed values: `portrait`, `landscape`.
title	String	`<title>` of the document shell.
format	ENUM	Default: `json`. Allowed values: `json`, `html`, `pdf`. `html` or `pdf` return the bytes; `json` returns the HTML as a data URI plus metadata.
download	Boolean	Default: `false`. Send `Content-Disposition: attachment` so browsers save the file.
markdown	Boolean	Default: `false`. Treat the rendered template as Markdown (CommonMark + tables) and convert it to HTML.
template	String	Jinja2 template in HTML or Markdown (≤ 256 KiB). Values are HTML-escaped; use `{{ value

Response

Returns a JSON object with metadata about the rendered output. The top-level fields are bytes integer, cache string, pages integer or null, engine string, format string, data_uri string, warnings array of strings, queued_ms integer, render_ms integer, media_type string, and engine_version string.

Parameter	Type	Description
bytes	Integer
cache	ENUM	Allowed values: `hit`, `miss`.
pages	Integer	PDF page count (null for DOCX/HTML).
engine	String
format	ENUM	Allowed values: `docx`, `pdf`, `html`.
data_uri	String	`data:<media_type>;base64,…`
warnings	String Array
queued_ms	Integer
render_ms	Integer
media_type	String
engine_version	String

Notes

format controls the response shape: json returns a data URI plus metadata, while html and pdf return bytes. If you render a fragment rather than a full <html> document, it is wrapped in a document shell with a pinned font stack; external stylesheet URLs are never fetched.

▣ COMMON ERRORS

Errors any endpoint can return

400bad_request

Required parameter missing or malformed body.

401unauthorized

API key missing, revoked, or not authorized for this service.

429rate_limited

Your plan's per-second rate exceeded. Retry with exponential backoff.

503upstream_busy

Backend temporarily unavailable. Try again in a few seconds.

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From the blog

Reads that touch this API.

Online DOCX to PDF Conversion and How to Handle ItSep 8, 2026 HTML to PDF API: What It Does and Why Teams Use OneAug 19, 2026 Generate Fast and Lightweight File Previews for docs, PDFs, DOCX, PPTX and more.Jul 9, 2026 Understanding Markdown and How to Convert It: A Developer’s GuideJul 9, 2026