Request detection

When one endpoint serves both a normal browser navigation and an htmx request, you need to know which one you are answering. Reach for request detection to return a fragment instead of a full page, to branch on boosted navigation, or to find out which element triggered the request.

Everything lives in the Htmx package (using Htmx;) as extension methods on HttpRequest plus the HtmxRequestHeaders and HtmxElementReference types.

Extension methods

All methods are on Htmx.HtmxHttpExtensions and accept a nullable HttpRequest.

Method	True when
IsHtmx()	HX-Request: true is present.
IsHtmx(out HtmxRequestHeaders? values)	Same, and values receives the parsed headers (null when not htmx).
IsHtmxBoosted()	An htmx request with HX-Boosted: true (a link or form enhanced by hx-boost).
IsHtmxNonBoosted() / IsHtmxNonBoosted(out values)	An htmx request that is not boosted (a plain hx-get, hx-post, …).
IsHtmxHistoryRestoreRequest()	HX-History-Restore-Request: true (back/forward re-fetch).
IsHtmxPartial()	htmx request with HX-Request-Type: partial.
IsHtmxFullRequest()	htmx request with HX-Request-Type: full.

Razor Pages

using Htmx;

public class ProductsModel : PageModel
{
    public IActionResult OnGet()
    {
        // Return only the list for htmx, the whole page otherwise.
        return Request.IsHtmx() ? Partial("_ProductList", this) : Page();
    }
}

MVC controllers

DemoController.cs

[HttpGet("request-headers")]
public IActionResult RequestHeadersEcho()
{
    var isHtmx = Request.IsHtmx(out var h);
    var isPartial = Request.IsHtmxPartial();
    var isFull = Request.IsHtmxFullRequest();
    var boosted = Request.IsHtmxBoosted();
    var nonBoosted = Request.IsHtmxNonBoosted();
    var restore = Request.IsHtmxHistoryRestoreRequest();
    // ... h.Source, h.SourceElement, h.Target, ...
}

Pair with Vary

If one URL returns different markup for htmx and non-htmx requests, tell caches. See Caching.

What htmx sends

A button click like this:

<button id="save" hx-post="/items" hx-target="#list">Save</button>

produces request headers similar to:

HX-Request: true
HX-Source: button#save
HX-Target: div#list
HX-Request-Type: partial
HX-Current-URL: https://localhost:5001/items

HX-Target is only sent when a target is set. HX-Boosted: true is added for boosted links/forms, HX-History-Restore-Request: true for history re-fetches, and HX-Prompt carries the answer to an hx-prompt (when that extension is in use).

HtmxRequestHeaders

Create it with new HtmxRequestHeaders(HttpRequest request) or receive it from IsHtmx(out var h).

Property	Header	Type / notes
Source	HX-Source	string, raw tag#id. Replaces htmx 2’s request HX-Trigger.
SourceElement	HX-Source	HtmxElementReference?, parsed.
Target	HX-Target	string, raw tag#id; only sent when a target is set.
TargetElement	HX-Target	HtmxElementReference?, parsed.
RequestType	HX-Request-Type	HtmxRequestType: Unknown = 0, Full = 1, Partial = 2.
CurrentUrl	HX-Current-URL	string, the browser URL at request time.
Boosted	HX-Boosted	bool
HistoryRestoreRequest	HX-History-Restore-Request	bool
Prompt	HX-Prompt	string, only with hx-prompt.
Trigger, TriggerName	n/a	Removed, see below.

HtmxRequestHeaders.Keys exposes the header-name constants (Boosted, CurrentUrl, HistoryRestoreRequest, Prompt, Request, RequestType, Source, Target) and Keys.All returns them as string[]. See the request header reference.

Removed in htmx 4

HtmxRequestHeaders.Trigger and TriggerName (htmx 2’s HX-Trigger / HX-Trigger-Name request headers) are [Obsolete(error: true)] and throw NotSupportedException. Use Source / SourceElement. See the migration guide.

HtmxElementReference

htmx 4 sends elements as <tag>#<id>, or just <tag> when the element has no id (tag lowercase, id URI-encoded).

Member	Meaning
TagName	e.g. button
Id	the id exactly as sent (still encoded), or null
DecodedId	URI-decoded id
Raw	the original header value
static bool TryParse(string? value, out HtmxElementReference result)	parse a header value yourself
constructor (string TagName, string? Id, string Raw)	it is a record; use it in tests

if (Request.IsHtmx(out var h) && h!.SourceElement is { TagName: "button", Id: "save" })
{
    // the request came from <button id="save">
}

if (HtmxElementReference.TryParse("input#my%20field", out var el))
{
    // el.TagName == "input", el.Id == "my%20field"
    // el.DecodedId == "my field"
}

HX-Request-Type and boosted navigation

HX-Request-Type is full when the request targets body or uses hx-select, and partial otherwise. That is the cleanest way to choose between a full layout and a fragment. Boosted links (hx-boost) typically swap the whole body, so they arrive as full and IsHtmxBoosted() is true:

Boosted.cshtml.cs

public void OnGet() => RequestType = Request.IsHtmx(out var h) ? h!.RequestType.ToString() : "n/a";

boosted = @Request.IsHtmxBoosted()
htmx    = @Request.IsHtmx()
plain   = @Request.IsHtmxNonBoosted()

Note

A boosted request is still an htmx request, so IsHtmx() is true for it. Use IsHtmxNonBoosted() when you specifically want the non-boosted ones.

Polling

Polling is just a repeating request, so detect it like any other (Request.IsHtmx()). Response.StopPolling() (status 286) is gone in htmx 4 and is [Obsolete(error: true)]. To stop, return content that no longer contains the polling element. See Response headers: stopping polling.

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See the live demos: run dotnet run --project samples/Htmx4.Sample and open /RequestHeaders (source) and /Boosted (source).

Related: Response headers, Caching, htmx 4 reference.