Solving the bug in Zoho Writer API for styling

Solving the bug in Zoho Writer API for styling

So... the Zoho Writer APIs for programatically creating a document do not respect a template's style. The result is that any document you generate via API needs to be manually, paragraph by paragraph, reformatted.  That bug alone is sufficient to render Writer almost unworkable for any real-world usage.  (Who is responsible for product management and design quality? Yes, it is another example of developer-led programming short-cuts in Zoho!)

However, after a day of messing about, I found a workaround.  See the following markdown exploration of the issue and how to manually set the fonts, etc to match a templated document. The big problem with this is, of course, it requires a manual update should any templates change, and it needs to be aligned to every possible template.  Not ideal.

Zoho - can you please alter the way Zoho Writer handles importing basic formatting (eg. HTML headers, etc.) so that they respect the Writer template's existing styles.  Sure it can't be that difficult.   Also not, this happens if you insert RTF into a merge field... so it is not just the APIs.  The lack of basical style support means the entire templating system and generation of docs is broken from the ground up.  There is no way we can risk generating docs for automatic download or emailing with the product ion the current state. 

If I have missed something obvious in the documentation, please let me know. I would be very happy to wrotng about this problem.

For everyone else, enjoy the code.



  1. # How to Preserve Template Styles When Using the Zoho Writer Merge API

    ## The Problem

    When using the Zoho Writer Merge API to generate documents from templates, the merged content does not inherit the template's custom paragraph styles. Instead, standard HTML tags like `<h1>`, `<h2>`, `<h3>`, and `<p>` are rendered with default styling (Liberation Serif, browser-default sizes, black text, bold headings) — completely ignoring the font families, colours, and sizes defined in the template's stylesheet.

    This means if your template defines Heading 1 as *Heuristica 18pt dark blue*, your merged `<h1>` content will appear as *Liberation Serif 24pt bold black* instead.

    ## Root Cause

    The Zoho Writer Merge API accepts HTML in richtext merge fields. However, when it processes standard HTML heading tags (`<h1>` through `<h6>`), it:

    1. Maps them to Writer's internal heading classes (`heading1`, `heading2`, etc.)
    2. Applies **default inline styles** on the rendered spans — overriding the template's CSS-defined styles
    3. HTML heading tags also carry **implicit bold** (`font-weight: bold`) which may not match the template

    The template's stylesheet defines styles like:

    ```css
    #editorpane div.heading1 span.zw-portion {
        font-family: Heuristica, Georgia;
        font-size: 18pt;
        color: rgb(0, 32, 96);
    }
    ```

    But the merge engine ignores these and applies its own defaults inline.

    ## The Solution

    Instead of using semantic HTML heading tags, use `<p>` tags for **all** content and apply the template's exact styles as inline CSS. This prevents Writer from applying default heading styles, and gives you full control over the rendered appearance.

    ### Step 1: Extract Your Template's Styles

    Open your template in Zoho Writer, save the page as HTML (browser "Save As"), and inspect the stylesheet block. Look for the `#editorpane div.headingN span.zw-portion` rules:

    ```css
    /* Example from an IBRS template */
    #editorpane div.heading1 span.zw-portion {
        font-family: Heuristica, Georgia;
        font-size: 18pt;
        color: rgb(0, 32, 96);
    }
    #editorpane div.heading2 span.zw-portion {
        font-family: Heuristica, Georgia;
        font-size: 14pt;
        color: rgb(192, 0, 0);
    }
    #editorpane div.heading3 span.zw-portion {
        font-family: Heuristica, Georgia;
        font-size: 12pt;
        color: rgb(128, 128, 128);
    }
    #editorpane span.zw-portion {
        font-family: 'Lato 2';
        font-size: 12pt;
    }
    ```

    ### Step 2: Build HTML with Inline Styles

    Instead of:

    ```html
    <!-- DON'T DO THIS — styles will be overridden -->
    <h1>Cloud Infrastructure Advisory</h1>
    <h2>Executive Summary</h2>
    <p>This report examines cloud adoption trends.</p>
    <ul>
        <li>Finding one</li>
        <li>Finding two</li>
    </ul>
    ```

    Do this:

    ```html
    <!-- DO THIS — inline styles match the template exactly -->
    <p style="font-family: Heuristica, Georgia; font-size: 18pt; color: rgb(0,32,96);">Cloud Infrastructure Advisory</p>
    <p style="font-family: Heuristica, Georgia; font-size: 14pt; color: rgb(192,0,0);">Executive Summary</p>
    <p style="font-family: 'Lato 2', Lato, sans-serif; font-size: 12pt;">This report examines cloud adoption trends.</p>
    <ul>
        <li style="font-family: 'Lato 2', Lato, sans-serif; font-size: 12pt;">Finding one</li>
        <li style="font-family: 'Lato 2', Lato, sans-serif; font-size: 12pt;">Finding two</li>
    </ul>
    ```

    Key points:
    - Use `<p>` tags for **everything** including headings — never `<h1>` through `<h6>`
    - Apply the template's exact `font-family`, `font-size`, and `color` as inline styles
    - Do **not** add `font-weight: bold` unless the template explicitly uses it
    - List items (`<li>`) also need inline styles

    ### Step 3: Pass to the Merge API

    Use the v2 Merge and Store endpoint to create a persistent Writer-native document:

    ```python
    import json
    import requests

    ACCESS_TOKEN = "your_access_token"
    TEMPLATE_ID = "your_template_id"  # The merge template document ID

    # Your styled HTML content
    styled_html = (
        '<p style="font-family: Heuristica, Georgia; font-size: 18pt; '
        'color: rgb(0,32,96);">Cloud Infrastructure Advisory</p>'
        '<p style="font-family: Heuristica, Georgia; font-size: 14pt; '
        'color: rgb(192,0,0);">Executive Summary</p>'
        '<p style="font-family: \'Lato 2\', Lato, sans-serif; font-size: 12pt;">'
        'This report examines cloud adoption trends.</p>'
    )

    # Merge data must be wrapped in {"data": [...]}
    merge_data = json.dumps({
        "data": [{"content": styled_html}]
    })

    # Output settings — use "zdoc" for native Writer documents
    output_settings = json.dumps({
        "doc_name": "My Report",
        "format": "zdoc"
    })

    response = requests.post(
        f"{BASE_URL}/writer/api/v2/documents/{TEMPLATE_ID}/merge/store",
        headers={"Authorization": f"Zoho-oauthtoken {ACCESS_TOKEN}"},
        data={
            "merge_data": merge_data,
            "output_settings": output_settings,
        },
    )

    result = response.json()
    record = result["records"][0]
    print(f"Document URL: {record['document_url']}")
    print(f"Document ID:  {record['document_id']}")
    ```

    ## Additional Gotchas Discovered

    ### 1. merge_data format

    The merge data **must** be wrapped in a `{"data": [...]}` array, even for a single record:

    ```json
    // WRONG — will return "Merge data not found" (R6001)
    {"content": "<p>Hello</p>"}

    // CORRECT
    {"data": [{"content": "<p>Hello</p>"}]}
    ```

    ### 2. Output format for editable documents

    Use `"format": "zdoc"` to create native Zoho Writer documents. Using `"format": "docx"` creates a Word file in WorkDrive that doesn't behave as a native Writer document.

    ### 3. No newlines in HTML content

    Do not include `\n` newline characters between HTML elements in the merge data. Writer renders these as literal line breaks in the document. Concatenate your HTML elements directly:

    ```python
    # WRONG — \n appears as visible line breaks
    html = "<p>Paragraph one</p>\n<p>Paragraph two</p>"

    # CORRECT
    html = "<p>Paragraph one</p><p>Paragraph two</p>"
    ```

    ### 4. OAuth scopes required

    The merge and store endpoint requires these scopes:

    ```
    ZohoWriter.documentEditor.ALL
    ZohoWriter.merge.ALL
    ZohoPC.files.ALL
    WorkDrive.files.ALL
    WorkDrive.organization.ALL
    WorkDrive.workspace.ALL
    ```

    The first two alone are not sufficient — the WorkDrive and ZohoPC scopes are also required, even for basic template and folder operations.

    ### 5. Template field type must be "richtext"

    Your merge template must have a field defined as `richtext` type to accept HTML content. You can verify fields via:

    ```
    GET /writer/api/v1/documents/{template_id}/fields
    ```

    Which returns:

    ```json
    {
        "merge": [
            {
                "id": "content",
                "type": "richtext",
                "display_name": "content",
                "category": "created"
            }
        ]
    }
    ```

    ## Helper Function: Content Builder

    Here is a reusable Python function that converts a structured content specification into correctly styled HTML for any template:

    ```python
    from html import escape

    # Define styles per template — extracted from the template's stylesheet
    TEMPLATE_STYLES = {
        "my_template": {
            "heading1": "font-family: Heuristica, Georgia; font-size: 18pt; color: rgb(0,32,96);",
            "heading2": "font-family: Heuristica, Georgia; font-size: 14pt; color: rgb(192,0,0);",
            "heading3": "font-family: Heuristica, Georgia; font-size: 12pt; color: rgb(128,128,128);",
            "paragraph": "font-family: 'Lato 2', Lato, sans-serif; font-size: 12pt;",
            "list_item": "font-family: 'Lato 2', Lato, sans-serif; font-size: 12pt;",
        },
    }

    def build_html(content_blocks, template_name=None):
        """
        Convert structured content blocks into styled HTML.

        content_blocks: list of dicts with keys:
            - type: "heading1", "heading2", "heading3", "paragraph",
                    "bullet_list", "numbered_list"
            - text: str (for headings/paragraphs)
            - items: list[str] (for lists)
        template_name: key into TEMPLATE_STYLES dict
        """
        styles = TEMPLATE_STYLES.get(template_name, {}) if template_name else {}
        parts = []

        for block in content_blocks:
            block_type = block.get("type", "paragraph")
            text = block.get("text", "")
            items = block.get("items", [])

            if block_type in ("heading1", "heading2", "heading3", "paragraph"):
                style = styles.get(block_type, "")
                attr = f' style="{style}"' if style else ""
                parts.append(f"<p{attr}>{escape(text)}</p>")

            elif block_type == "bullet_list":
                style = styles.get("list_item", "")
                attr = f' style="{style}"' if style else ""
                li = "".join(f"<li{attr}>{escape(item)}</li>" for item in items)
                parts.append(f"<ul>{li}</ul>")

            elif block_type == "numbered_list":
                style = styles.get("list_item", "")
                attr = f' style="{style}"' if style else ""
                li = "".join(f"<li{attr}>{escape(item)}</li>" for item in items)
                parts.append(f"<ol>{li}</ol>")

        return "".join(parts)  # No \n between elements!


    # Usage
    content = [
        {"type": "heading1", "text": "Cloud Infrastructure Advisory"},
        {"type": "heading2", "text": "Executive Summary"},
        {"type": "paragraph", "text": "This report examines cloud adoption."},
        {"type": "bullet_list", "items": ["Finding one", "Finding two"]},
        {"type": "heading3", "text": "Recommendations"},
        {"type": "numbered_list", "items": ["Action one", "Action two"]},
    ]

    html = build_html(content, template_name="my_template")
    ```

    ## Summary

    | What | Don't | Do |
    |------|-------|----|
    | Heading tags | `<h1>`, `<h2>`, `<h3>` | `<p style="...">` |
    | Styling | Rely on template CSS inheritance | Inline the template's exact styles |
    | Bold | Let heading tags add implicit bold | Only add `font-weight` if the template uses it |
    | merge_data | `{"field": "value"}` | `{"data": [{"field": "value"}]}` |
    | Output format | `"docx"` | `"zdoc"` for native Writer |
    | HTML joins | `"\n".join(parts)` | `"".join(parts)` |

    This approach preserves the visual identity of your Zoho Writer templates when programmatically generating documents through the Merge API.

    ---

    *Tested with Zoho Writer API v1/v2, April 2026*





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