How to upload files with Playwright, and verify it landed

To upload a file with Playwright, call page.set_input_files(selector, path) when the page has an <input type="file">, or use page.expect_file_chooser() when the input only appears after a click. Both run through the automation driver, so the file attaches with trusted (isTrusted: true) events and no native OS window ever appears on screen.

Uploading a file looks like it should be the fiddly part of an automation, and it is usually the opposite: the driver does the OS dialog for you and you never see a native window. The part worth understanding is not the syntax, it is why the correct method is also the safe one, and where it is not enough on its own.

This page covers the two upload paths Playwright gives you, why both are handled at the driver level rather than by faking a page event, multiple files and in-memory buffers, the one honest caveat about behaviour, and how to confirm the file actually attached.

Everything here uses stock Playwright. InvisiblePlaywright returns a real playwright.sync_api.Browser, so every method below is the upstream method, documented exactly as upstream documents it.

Situation	Method to use
The page exposes an <input type="file"> you can select	set_input_files(selector, path)
The input only exists after clicking a custom button	expect_file_chooser(), then set_files(...)
Several files at once	pass a list of paths (or buffer dicts) in one call
Content generated at runtime, no file on disk	pass a {name, mimeType, buffer} dict to either method

The simple case: set_input_files

If the page has an <input type="file"> element, you do not click it and you do not open a dialog. You point the input at a path.

from invisible_playwright import InvisiblePlaywright

with InvisiblePlaywright(seed=42) as browser:
    page = browser.new_page()
    page.goto("https://example.com/upload")

    page.set_input_files("input[type=file]", "report.pdf")
    page.click("#submit")

set_input_files takes the selector and one or more paths, and it works whether or not the input is visible. Many sites hide the real <input> behind a styled button; you can still target the hidden input directly by selector, and you do not have to make it visible first.

Clearing a selection is the same call with an empty list:

page.set_input_files("input[type=file]", [])

Using a locator instead of a raw selector reads better when the input is nested and you have already scoped to a form:

form = page.locator("form#profile")
form.locator("input[type=file]").set_input_files("avatar.png")

When the input is hidden behind a custom control: the file chooser

Some upload widgets have no reachable <input> at all until you click their button, because the input is created on demand. For those, listen for the chooser the click opens instead of hunting for a selector.

with page.expect_file_chooser() as fc_info:
    page.click("text=Add a file")     # the click that opens the native dialog
file_chooser = fc_info.value
file_chooser.set_files("report.pdf")

expect_file_chooser() arms a listener, the click inside the with block triggers the browser’s file dialog, and set_files answers it. The native OS window never appears on screen; Playwright intercepts the chooser and fills it from the driver. This is the path to reach for when the DOM does not expose an input you can target directly.

Note that the click here is a real driver click, so on a browser that draws pointer motion it arcs to the button on a curve like any other click rather than teleporting to it.

Why this path is trusted, not a synthetic event

set_input_files and expect_file_chooser are the right methods, and a hand-rolled JavaScript alternative is not, because only the driver path produces trusted events. A file assigned by page script fires a change event carrying isTrusted: false, which is a permanent, browser-set tell; the driver path fires isTrusted: true, exactly as a human picking a file from the OS dialog would.

You cannot upload a file by constructing an event in page JavaScript. For security, the browser will not let page script assign a real file to an input’s files property, and any change event you dispatch yourself arrives carrying isTrusted: false. That flag is set by the browser and is not writable, so a scripted dispatch is permanently marked as script-made. It is the same distinction that separates a driver click from a fake one dispatched from the page: element.dispatchEvent(...) is isTrusted: false forever, while input driven through the automation driver is generated inside the browser and comes out genuinely trusted.

set_input_files and expect_file_chooser both go through the driver, not through page JavaScript. The file assignment and the change/input events that follow it are produced by the browser’s own input path, so they carry isTrusted: true exactly as a human picking a file from the OS dialog would. That means the upload is not the cheapest-check tell that a scripted dispatchEvent would be: a page that reads event.isTrusted on the file input sees a trusted event, because it is one.

InvisiblePlaywright does not change any of this; it is standard Playwright behaviour. What the patched engine adds is elsewhere - the pointer motion, the fingerprint - not in how the file attaches. The upload path is safe on plain Playwright and stays safe here.

Multiple files, buffers, and files you never wrote to disk

set_input_files accepts a list, so multi-file inputs are one call:

page.set_input_files("input[type=file]", ["a.pdf", "b.png", "c.csv"])

You do not need a file on disk at all. Pass a dict with a name, a MIME type and the bytes, and the upload comes straight from memory - useful when the content is generated in the run and there is no reason to touch the filesystem:

page.set_input_files(
    "input[type=file]",
    files=[{
        "name": "data.csv",
        "mimeType": "text/csv",
        "buffer": b"col_a,col_b\n1,2\n3,4\n",
    }],
)

The same buffer form works on the file chooser:

with page.expect_file_chooser() as fc_info:
    page.click("text=Attach")
fc_info.value.set_files({
    "name": "note.txt",
    "mimeType": "text/plain",
    "buffer": b"generated in the run\n",
})

The async API is identical with await in front of each call:

from invisible_playwright.async_api import InvisiblePlaywright

async with InvisiblePlaywright(seed=42) as browser:
    page = await browser.new_page()
    await page.goto("https://example.com/upload")
    await page.set_input_files("input[type=file]", "report.pdf")

The one behavioural caveat, and how to work with it

The honest limit is not about the fingerprint, it is about behaviour. set_input_files does exactly one thing: it attaches the file and fires the trusted events. It does not move the pointer, it does not open a visible dialog, and it takes no measurable time. On a site that only checks the events, that is complete and correct. On a site that also watches behaviour, an upload that appears with no interaction leading up to it can be as out of place as a click with no pointer motion before it.

The fix is not to fake the dialog, which you cannot do trustedly anyway. It is to drive the visible control the way a person would and let set_input_files do the attaching:

page.hover("#upload-button")     # arcs to the control
page.click("#upload-button")     # the click a human makes
page.set_input_files("input[type=file]", "report.pdf")

Whether that matters at all depends on whether the site watches behaviour, which is a question worth settling before adding motion you do not need - the ordering to work through is in the checklist for being detected on one site. The pointer path itself has its own subtlety on the hover call specifically, covered in why humanized motion can collapse on hover().

Verifying the upload actually landed

An upload that silently attached nothing is worse than one that errored, because it looks fine. Assert the presence of the result rather than the absence of an error, the same rule as testing any other surface: a blank result is a failure, not a pass.

Read the input’s own file list back:

count = page.eval_on_selector(
    "input[type=file]",
    "el => el.files.length",
)
assert count == 1, f"expected 1 file attached, got {count}"

name = page.eval_on_selector(
    "input[type=file]",
    "el => el.files[0]?.name",
)
assert name == "report.pdf"

Then confirm the server accepted it, by waiting for whatever the page shows on success rather than assuming the submit worked:

page.click("#submit")
page.wait_for_selector("text=Upload complete", timeout=15000)

If the flow is part of a longer authenticated session, do the login once and reuse the saved state instead of re-authenticating each run - the pattern is in scraping behind a login - so the upload runs against a warm session rather than the highest-scrutiny sequence on the site.

Conclusion

File upload is one of the places where the correct Playwright method and the safe method are the same method. set_input_files and expect_file_chooser both go through the driver, so the file attaches with trusted events that a page reading isTrusted cannot tell from a human’s, while the JavaScript alternative is both blocked by the browser and marked as script-made. Use the buffer form when the content is generated in the run, add pointer motion only if the site watches behaviour, and verify the file list and the success state instead of trusting a call that returned without raising.

Short answers to the questions that lead here

How do I upload a file with Playwright? page.set_input_files("input[type=file]", "report.pdf"). It works whether or not the input is visible, and it does not open a native window.

The upload button has no file input I can select. What now? Use page.expect_file_chooser(), click the button inside the with block, and call set_files on the chooser the click opens.

Can I upload without writing the file to disk? Yes. Pass a dict with name, mimeType and buffer (the bytes) instead of a path, to either set_input_files or the chooser’s set_files.

Is set_input_files detectable as automation? The events it fires are trusted (isTrusted: true), because the driver produces them in the browser. A change event you dispatch from page JavaScript is isTrusted: false permanently, which is the tell.

How do I upload more than one file? Pass a list of paths, or a list of buffer dicts, in a single set_input_files call.

How do I check the upload actually attached? Read el.files.length back off the input with eval_on_selector, then wait for the page’s own success indicator rather than assuming the submit worked.

Sources

• The upstream Playwright API for set_input_files and expect_file_chooser and FileChooser.set_files, which InvisiblePlaywright exposes unchanged because the returned object is a real Playwright Browser.
• The isTrusted event property, which the upload path’s trust argument rests on: read-only, set by the browser, true only for events the browser itself generated.

See also: human-like mouse movement and the trusted-event distinction, the checklist for being detected on one site, and scraping behind a login.

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Written while maintaining invisible_playwright, a Firefox patched at the C++ level driven by stock Playwright. The upload path is plain Playwright; what makes it safe is the same trusted-event boundary the pointer work leans on.