Title: Pass details into a form with hidden fields | OneForm > Add a client number, a referral or a campaign name to your form's link, and get it back with the answers without asking. Source: https://oneform.si/help/share/prefill-answers-and-hidden-fields/ --- 1. [Help Center](https://oneform.si/help/) 2. [Sharing and embeds](https://oneform.si/help/share/) 3. Pass details into a form with hidden fields [View as Markdown](https://oneform.si/help/share/prefill-answers-and-hidden-fields.md) # Pass details into a form with hidden fields Add a client number, a referral or a campaign name to your form's link, and get it back with the answers without asking. Admins and ownersUpdated October 22, 2026 · 2 min read [Open your forms ↗](https://app.oneform.si/forms?help=prefill-answers-and-hidden-fields) Hidden fields carry details in the form's link that clients never see or type: a client number, the name of a campaign, who referred them. They arrive with the answers, so you know exactly where each response came from. For example, `/f/tax-checkup?client_id=1042` fills the hidden field `client_id` with `1042`. ## Add a hidden field ![The Hidden fields card on the form's Settings tab, with the Add hidden field button](https://app.oneform.si/media/101114a1-eda9-5a8e-9be6-3d984cf8125b) 1. Go to [Forms](https://app.oneform.si/forms) and open the form. 2. Click the **Settings** tab and scroll to **Hidden fields**. 3. Click **Add hidden field**. 4. Type its name, like `client_id`. Use letters, numbers, dashes and underscores. 5. Optionally, give it a **Label**. That's the name your team sees with the answers. Changes save as you make them. ## Put a value in the link 1. Copy the form's link from the **Share** tab. 2. Add `?`, the hidden field's name, `=`, and the value: `?client_id=1042`. 3. For more than one, join them with `&`: `?client_id=1042&ref=smith`. Send each client a link with their own value. Spaces and symbols need encoding in a link, so stick to letters, numbers and dashes in values where you can. ## Campaign tags work without setup The five standard campaign tags are always kept, even if you didn't add them as hidden fields: `utm_source`, `utm_medium`, `utm_campaign`, `utm_term` and `utm_content`. Use them on links in ads, newsletters and social posts: `?utm_source=newsletter&utm_campaign=spring`. ## On your website When the form is on your website, details can come from the page's own link instead. On the **Share** tab, under **Add to your website**, type the names in **Pass details from your page's link into the form**, for example `ref, client_id`. A visitor who lands on `yourfirm.com/tax?ref=smith` then brings `ref=smith` into the form. Campaign tags on the page's link always come through. ## Where the values show up - **With the response.** Open it on the **Responses** page: they're under **Extra details from the link**. - **In downloads.** Each one gets its own column, marked "(hidden)". - **In the report.** OneFormAI reads the hidden fields you added, so your report instructions can use them. It doesn't read campaign tags. - **In your questions and logic.** Use them in **Insert answer**, in show-and-hide rules, and to pick an ending. See [Logic and branching](https://oneform.si/help/forms/logic-and-branching/). - **On the Leads page.** Campaign tags become the lead's source. A `ref` value, or "refer" in a campaign tag, counts as a referral in the lead score. See [Leads explained](https://oneform.si/help/responses-and-leads/leads-explained/). ## Good to know - **Only names you added are kept.** Anything else in the link is ignored, so nobody can slip extra data in. - **Values are cut to 300 characters.** - **Hidden fields don't fill in questions.** To have clients confirm a detail, ask it as a question. ## Why is my hidden field empty? - **The name in the link doesn't match.** `clientid` and `client_id` are different names. Check the spelling on the **Settings** tab. - **The value was dropped on the way.** Some email and ad tools rewrite links. Open the link you actually sent and check that the `?name=value` part is still there. Was this article helpful? [← PreviousPut a form on your website](https://oneform.si/help/share/embed-a-form-on-your-website/)[Next →Follow up on unfinished forms](https://oneform.si/help/share/unfinished-forms/) ## Related articles [Share a form linkCopy your form's link, change the end of it, and check what clients will see before you send it.](https://oneform.si/help/share/share-a-form-link/)[Put a form on your websiteChoose how your form appears on your site (in the page, a popup, a slider, a chat bubble or a button), preview it, and paste the code.Basic plan and up](https://oneform.si/help/share/embed-a-form-on-your-website/)[FormsLogic and branchingShow questions only when they apply, skip ahead based on answers, add up scores, and send people to different endings.](https://oneform.si/help/forms/logic-and-branching/)[FormsPersonalize questions with answersGreet clients by name and repeat their earlier answers, scores or link details in later questions and on the thank-you screen.](https://oneform.si/help/forms/personalize-questions-with-answers/) Still stuck? 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