Step-by-step guide

How to prove what changed on a web page

This guide, written for the October 2026 ProofSnap Dashboard, shows how to prove what changed on a web page: compare two captures of the same page, review the text, images and metadata that changed, and download the comparison as its own sealed evidence package, alongside the two unchanged originals.

By Radim Motycka, Founder and Lead Engineer at ProofSnap, who built the dashboard, the API and the capture pipeline this guide walks through. ·

Where

Tools > Compare captures

Cost

Counts as one capture

You get

A sealed evidence package

What this guide is for

Use it when you need to show that something on a web page changed between two dates: a price on a pricing page, a clause in the Terms of Service, a claim on a product page, or a returns or privacy policy. You capture the page on each date; ProofSnap then compares the two sealed versions and lists the text removed and added, the images that changed and the metadata fields that differ. Both captures stay exactly as they were sealed, and the comparison is sealed as a separate evidence package. Instead of two screenshots side by side, you hand over one dated report that can be checked without ProofSnap.

Before you start

  • A ProofSnap Dashboard account on a paid plan that can make captures. Comparisons are not available in sandbox mode or on Archive only. New to the dashboard? Start with Getting started with the dashboard.
  • Two completed captures of the same public page, taken on different dates. The dashboard captures from ProofSnap's servers without your cookies, so a page behind a login or a paywall cannot be captured for a comparison here.
  • The same device profile (Desktop or Mobile) and the same capture options for both captures.

Step 1

Get two captures of the same page

A comparison works on two captures you already have. Capture the page in New capture on the first date and again on the second, or let an automated capture run on a schedule. Use the same device profile and the same capture options both times, so that only the content can differ.

  1. 1New capture. One capture per date, started manually. See Make your first capture.
  2. 2Automated captures. Capture the page on a schedule, or each time its text changes, with the same settings at every run unless you edit them. See How to monitor web page changes as evidence.
  3. 3Capture history. Both captures must show Completed. The type column shows the device of a web page capture, Desktop or Mobile; an automated capture shows Automated with the device below it.
New capture, Automated captures and Capture history, simplified. The page and the dates are examples.

Step 2

Open Compare captures

Sign in at app.getproofsnap.com and open Tools. The Compare captures tab sits between Verify a package and Certify a file. The Compare link at the top of Capture history opens the same tab.

  1. 1Tools. The section with the dashboard's standalone utilities.
  2. 2Compare captures. The tab that holds the comparison tool.
  3. 3Compare. The shortcut in the header of Capture history, next to Deletion and hold log.
The Tools section and the header of Capture history, simplified.

Step 3

Choose Before and After

Click the Before field and type part of the page address to find your captures. Pick the earlier capture, then pick the later one in After. Only completed web page captures appear in the lists. If your two newest captures are of the same page and were taken with the same settings, the dashboard fills them in for you.

  1. 1Before. The empty field reads Choose the earlier capture. The list groups the captures by page address, and each entry shows the date, the device and the capture ID. Once picked, the field shows the date, the page address and the capture ID.
  2. 2Swap. Exchanges Before and After. If the capture chosen as Before was taken later than the one chosen as After, a note under the fields says so and offers its own Swap.
  3. 3After. The empty field reads Choose the later capture. An entry taken on a different device or with different settings from the capture in the other field is tagged Different device or Different settings.
Choosing the two captures, simplified. The page, the dates and the IDs are examples.

Step 4

Check the warnings

Two notes can appear under the fields before you compare. They are there because a difference in how a page was captured can look like a change in the page itself.

  1. 1Different pages. The two captures are of different pages. You can still compare them: the confirmation in step 5 repeats the note and asks you to confirm.
  2. 2Different device or settings. For example The captures were taken on different devices (Desktop / Mobile). Text and layout can differ even if the content did not change. A settings difference names the settings instead.
  3. 3Compare anyway. Such a pair is compared only when you tick this box. The text and image result is then shown as Undetermined, because the difference may come from the capture conditions alone. For a clean result, take a new capture with matching settings instead.
Both warnings at once, simplified. The pages and the dates are examples.

Step 5

Set the report and run the comparison

Under Comparison report, choose the language of the evidence PDF and, if you need one, an eIDAS timestamp. Then click Compare and confirm. Before comparing, ProofSnap recomputes the hash of every file in both source packages and checks it against the sealed manifest of its package.

  1. 1Evidence PDF language. Any of 29 languages. Default (dashboard language) uses the language the dashboard is shown in.
  2. 2Add qualified electronic timestamp (eIDAS). Optional, as with a capture: a qualified timestamp from Disig a.s., a Qualified Trust Service Provider on the EU Trusted List, billed extra at $1.99 per stamp. Not available in sandbox mode.
  3. 3Compare. The line next to the button reads Counts as one capture.
  4. 4Run this comparison? Confirm with Compare or step back with Cancel. While it runs, the dashboard shows Comparing…
The report options and the confirmation, simplified. The eIDAS price line shows when your plan bills eIDAS stamps.

Step 6

Read the result

The result appears under the button as soon as the comparison finishes. It opens with one sentence: The page content changed, No differences detected or, for two captures taken under different conditions, a note that this cannot be reliably determined. Three tiles follow, for the images, the text and the metadata.

  1. 1Images changed. Images from the page's own site that were replaced, added or removed, based on the image inventory each capture sealed, for example 0 from the page's site. Images from other domains are shown on a line of their own and not counted. If a capture holds no usable image inventory, a note says that the images were not compared.
  2. 2Text. Compared line by line: the share of the text that changed, for example 1.8% changed, and the lines added and removed.
  3. 3Metadata. How many page fields differ. Step 8 shows which ones.
The top of a comparison result, simplified. The figures are examples.

Step 7

Read what changed on the page

Below the tiles, What changed on the page puts the removed text and the added text in two columns, each sorted from the top of the page down, so that changes made at the same place line up. Removed text is struck through; added text carries a plus sign.

  1. 1Removed and Added. Each column head counts its entries, for example Removed: 1.
  2. 2Change 1. The same number marks this place in the evidence PDF (step 9).
  3. 3≈38%. How far down the page the change is: 0% is the top, 100% the bottom. The legend above the columns says the same.
  4. 4Many changes. The dashboard lists those highest on the page, shows the total and notes that everything is in the ZIP.
What changed on the page, simplified. The clause and its position are examples; the last line appears only when the list is shortened.

Step 8

Check the page metadata

Under the changed text, a table lists each page field that differs, with its Before and After values. Only fields that describe the page content count as a change.

  1. 1Counted fields. Address, Final address (after redirects), Page title, HTTP status and Content type.
  2. 2Technical fields, not counted. A folded list of fields that only describe how the page was served or rendered, such as Server, Connected IP address, TLS issuer, Window width or Browser (User-Agent). They are shown for information only and never count as a change.
  3. 3Device profile. When only the device differs, the Metadata tile says so, for example Device profile differs (Desktop / Mobile).
The metadata part of a result, simplified. The values are examples, and the last tile appears only when the device is the sole difference.

Step 9

Open the evidence PDF

The comparison package contains evidence.pdf, in the language you chose in step 5. It is the document to read or share: it sums up the result and shows where the page changed, so nobody has to open the technical files.

  1. 1Result. One sentence in bold, then one line each for the text, the images and the metadata. The report also names both source captures by their capture ID and the time each was captured.
  2. 2Where the text changed. Up to 10 places, numbered from the top down. Each shows a Before and an After cut-out of the sealed screenshots of the two source packages, side by side, with the changes outlined.
  3. 3Caption. For example Change 1: 38% from the top, the same number as in the dashboard. The complete screenshots stay in the source packages.
The evidence PDF of a comparison, simplified. In the real PDF the cut-outs are images from the sealed screenshots; the changes are examples.

Step 10

Download the sealed comparison package

Every comparison is saved in Capture history with the type Compare, next to your captures. The two captures you compared stay exactly as they were sealed. Download the comparison package from the result or from its row, as often as you need.

  1. 1Type: Compare. Choose it in the type list of Capture history, which reads All types by default, to list only your comparisons.
  2. 2Compare. The type of the entry. Each comparison is its own sealed evidence package, with its own hashes, signed manifest and timestamps.
  3. 3Download ZIP. The comparison package, including compare.json, image_changes.json, change_regions.json, text_diff.patch, comparison_method.json, evidence.pdf, the signed manifest and, when the OpenTimestamps calendars answered, the OpenTimestamps proof. The full list is in the questions below.

The OpenTimestamps proof shows that the package existed no later than the time it records; the RSA signature shows that no file has changed since sealing. To check a comparison package, follow How to verify an evidence package, as with any ProofSnap package.

Capture history filtered to comparisons, simplified: the real list is a table with more columns and row actions. The pages and the dates are examples.

Common questions

Related guides

Two captures of the same page?

Open the dashboard, then go to Tools > Compare captures.

Open the ProofSnap Dashboard

More: Monitor web page changes · Verify an evidence package · API documentation

Open the ProofSnap Dashboard