Adding model-wide help text to a django model's admin form

Use the admin's fieldsets:

class MyAdmin(admin.ModelAdmin):
    fieldsets = (
        (None, {
            'fields': ('first', 'second', 'etc'),
            'description': "This is a set of fields group into a fieldset."
        }),
    )
    # Other admin settings go here...

You can have multiple fieldsets in an admin. Each can have its own title (replace the None above with the title). You can also add 'classes': ('collapse',), to a fieldset to have it start out collapsed (the wide class makes the data fields wider, and other class names mean whatever your CSS says they do).

Be careful: the description string is considered safe, so don't put any uncleaned data in there. This is done so you can put markup in there as needed (like your link), however, block formatting (like <ul> lists) will probably look wrong.

There is a fairly simple, yet underdocumented way of accomplishing this.

Define render_change_form in the Admin class

First, you need to pass extra context to your admin. To do this, you can define a render_change_form function within your admin Class, e.g.:

# admin.py
class CustomAdmin(admin.ModelAdmin):
    def render_change_form(self, request, context, *args, **kwargs):
        # here we define a custom template
        self.change_form_template = 'admin/myapp/change_form_help_text.html'
        extra = {
            'help_text': "This is a help message. Good luck filling out the form."
        }

        context.update(extra)
        return super(CustomAdmin, self).render_change_form(request,
            context, *args, **kwargs)

Creating a custom template

Next, you need to create that custom template (change_form_help_text.html) and extend the default 'admin/change_form.html'.

# change_form_help_text.html
{% extends 'admin/change_form.html' %}
{% block form_top %} 
{% if help_text %}<p>{{ help_text }}</p>{% endif %}
{% endblock %}

I've chosen to place this template inside templates/admin/myapp/, but this is also flexible.

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More info available at:

http://davidmburke.com/2010/05/24/django-hack-adding-extra-data-to-admin-interface/

http://code.djangoproject.com/wiki/NewformsHOWTO#Q:HowcanIpassextracontextvariablesintomyaddandchangeviews

If I understand what you want the code below should do what you want.

def __init__(self, *args, **kwargs):
        super(ClassName, self).__init__(*args, **kwargs)
        if siteA:
            help_text = "foo"
        else:
            help_text = "bar"
        self.form.fields["field_name"].help_text = help_text

That's an example of using some logic to modify an overriden form. So you just put this in your ModelAdmin constructor that you overrode.