DocGen Guide 128 tools · prices checked 20 Oct 2026 Find my tool
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Letter generators for JSON API

If you need a letter built from JSON sent to an API, 16 tools here can make one. The first three in our order are Fluent (Windward), Xpertdoc and Knackly. Of these, 7 have a free tier.

Tools
16
With USD price
9, from $15
Free tier
7
Direct / via Zapier
13 / 3
Checked
20 Oct 2026
  1. 01
    Fluent (Windward) windwardstudios.com

    Formerly Windward Studios, acquired by PDFTron (now Apryse).

    Outputs PDF, DOCX, XLSX, PPTX, HTML Template Word Also reads Salesforce, Excel G2 4.4 (77)
    On request
  2. 02
    Xpertdoc xpertdoc.com

    CCM and document generation with Microsoft Dynamics CRM connector.

    Outputs PDF, DOCX, email, e-sign documents Template Word G2 4.3 (26)
    On request
  3. 03
    Knackly knackly.io

    Legal document automation.

    Outputs DOCX, PDF Template Word Also reads built-in forms, Zapier/Make/n8n
    $209 / mo
  4. 04
    Templafy templafy.com

    AI document agents in Microsoft Office.

    Outputs PPTX, DOCX, PDF Template Word Also reads Salesforce
    $40 / mo
  5. 05
    Docmosis docmosis.com

    Cloud Professional $49/mo, 4,000+ pages.

    Outputs PDF, DOCX, HTML Template Word
    $49 / mo
  6. 06
    Docxpresso docxpresso.com

    EUR pricing shown as Core 2500 EUR/user/mo (likely 25.00, formatting unclear).

    Outputs PDF, DOCX Template Word Also reads built-in forms
    $27 EUR 25/user, converted
  7. 07
    docxtemplater docxtemplater.com

    JS library, MIT/GPLv3 core.

    Outputs DOCX, PPTX, XLSX Template Word
    $45 EUR 500/yr, converted
  8. 08
    Inkit inkit.com

    Secure document generation and e-sign.

    Outputs PDF, e-sign documents Template HTML
    $15 / mo, cheapest here
  9. 09
    Aspose.Words products.aspose.com

    SDK. Developer Small Business license $1,679 perpetual.

    Outputs PDF, DOCX, HTML, Markdown Template Word
    On request
  10. 10
    docassemble docassemble.org

    MIT guided-interview and document assembly.

    Outputs PDF, DOCX Template Word, PDF form Also reads built-in forms
    Free
  11. 11
    HotDocs mitratech.com

    Owned by Mitratech. Desktop and cloud.

    Outputs DOCX, PDF Template Word Also reads built-in forms
    On request
  12. 12
    Adobe Document Generation API developer.adobe.com

    Part of Adobe PDF Services.

    Outputs PDF, DOCX Template Word
    On request free tier
12 of 16 shown Show the other 4Hide the other 4
  1. 13
    Wordize wordize.com

    Programmatic document processing SDK.

    Outputs DOCX, PDF Template Word
    Not published
  2. 14
    Gavel Editor's pick via Zapier gavel.io

    Formerly Documate (Documate Inc. dba Gavel).

    Outputs DOCX, PDF Template Word, PDF form Also reads built-in forms, Zapier/Make/n8n
    $83 / mo
  3. 15
    Documentero via Zapier documentero.com

    Micro $19.50/mo shown; price formatting unclear on page.

    Outputs DOCX, XLSX, PDF Template Word Also reads Google Sheets, CSV, Excel, Zapier/Make/n8n +1
    $19.50 / mo
  4. 16
    Crove via Zapier crove.app

    Individual $33/mo billed $390/yr.

    Outputs PDF, DOCX, e-sign documents Template Word, Visual builder Also reads built-in forms, Zapier/Make/n8n
    $33 / mo

What differs for JSON API

For letters built from JSON sent to an API, the lowest paid starting price is $15 a month, from Inkit. Published starting prices run from $15 to $209 a month, the top end from Knackly.

These tools for letters most often write PDF (15), DOCX (15) and PPTX (3). Among them, 3 need Zapier, Make or n8n to read JSON sent to an API, so they sit after the tools with a direct connection. Your own code decides when to call the API, so a document can be built on any event. Prices were checked on 20 Oct 2026.

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