# Filters
A filter changes a value as it is written into a document. Put it after the value with `|`, and give it any values it needs in brackets:
```jinja
{{ form.DraftFormName|upper }}
{{ form.als_fields_set.count() }} field{{ form.als_fields_set.count()|pluralize }}
```
Filters can follow one another, each working on what the one before it gave. To apply a filter to a whole block of a template rather than one value, use `{% filter %}`:
```jinja
{% filter upper %}
This text is written in capitals.
{% endfilter %}
```
This page lists every filter a Document Template can use. Any other filter name stops the template with an error.
The examples use three values a real template would get from its data: `when`, a date and time of 5 March 2026 14:30 UTC; `forms`, three Forms with OIDs DM, AE and VS, of which AE is inactive; and `form`, the first of them. The **Gives** column is exactly what each example writes into the document.
## Values are escaped
Text written into a document has `&`, `<`, `>` and quotes replaced by their escaped forms, so a value cannot break the document's markup. This is why `Fish & Chips` is written as `Fish & Chips`. Filters that produce markup on purpose, such as `markdown` and `clean_html`, mark their result as safe so it is not escaped a second time.
This happens in every type of Template, Text included. A Text Template that writes plain text, Markdown or CSV rather than XML should write its values with `safe`, as in `{{ form.DraftFormName|safe }}`, so that they appear exactly as they are stored.
Two things are not escaped. The text the `{% ai %}` tag writes is used exactly as it comes back, and [The AI tag](ai_tag.html.md#document-template-ai-tag) lists the filters to use on it. The result of a `{% filter %}` block is not escaped again either, but the values inside it already were, so a filter that changes letters can break them: `{% filter upper %}{{ "Fish & Chips" }}{% endfilter %}` writes `FISH & CHIPS`. Apply such a filter to the value instead: `{{ "Fish & Chips"|upper }}`.
## Filters added by TrialGrid
| Filter | What it does | Example | Gives |
| --- | --- | --- | --- |
| `chunk` | Splits a list into lists of the length you give. The last one holds what is left. | `{% for row in [1, 2, 3, 4, 5]\|chunk(2) %}[{{ row\|join(" ") }}] {% endfor %}` | `[1 2] [3 4] [5]` |
| `clean_html` | Keeps only the HTML tags you list and removes the others, keeping their text. With no list, keeps a standard set of text formatting tags. On a Word, Excel or PDF Template, follow it with `convert_html`. | `{{ "Hello there
"\|clean_html(["p"]) }}` | `Hello there
` |
| `convert_html` | Turns HTML into Word or Excel formatting, so bold, lists and paragraphs appear as they would on a web page. Only in Word and Excel Templates. | | |
| `date` | Writes a date and time as year, month and day. Gives nothing for an empty value. | `{{ when\|date }}` | `2026-03-05` |
| `format_datetime` | Writes a date and time in the format you give, using the codes in [Python Date Formats](https://docs.python.org/3/library/datetime.html#strftime-and-strptime-format-codes). Gives nothing for an empty value. | `{{ when\|format_datetime("%d %b %Y %H:%M") }}` | `05 Mar 2026 14:30` |
| `html_sanitize` | Removes HTML tags and attributes that are not on a fixed list of safe formatting, keeping their text. | `{{ "Bold"\|html_sanitize }}` | `Boldx()` |
| `iso` | Writes a date and time in the ISO 8601 format. Gives nothing for an empty value. | `{{ when\|iso }}` | `2026-03-05T14:30:00+00:00` |
| `line_breaks_br` | Escapes the text, then turns each line break into `
`. On a Word or Excel Template, follow it with `convert_html`. | `{{ "one\ntwo"\|line_breaks_br }}` | `one
two` |
| `markdown` | Turns Markdown into HTML. Any HTML already in the text is removed first. On a Word or Excel Template, follow it with `convert_html`. | `{{ "Some **bold** text"\|markdown }}` | `Some bold text
` |
| `normalize_decimal` | Writes a decimal number without trailing zeros or scientific notation. Any other value is written as it is. | `{{ 2.50\|normalize_decimal }}` | `2.5` |
| `pluralize` | Applied to a number, gives `s` unless the number is 1, for adding to a word. For other endings, give the singular and plural ending separated by a comma. | `3 Form{{ 3\|pluralize }}, 1 Form{{ 1\|pluralize }}, 2 Entr{{ 2\|pluralize("y,ies") }}` | `3 Forms, 1 Form, 2 Entries` |
| `remove_line_break` | Joins the lines of a text into one line, with a space between each. HTML in the text is escaped, so it is shown rather than used. | `{{ "one\ntwo"\|remove_line_break }}` | `one two` |
| `rml_sanitize` | Turns HTML into the markup a PDF Template's paragraphs accept. Links are removed and their text kept, unless you pass `True`. | `{{ "See this
"\|rml_sanitize }}` | `See this` |
| `safe_json` | Marks JSON text as safe to place inside a `