# Backfill

> Run a prompt, custom or standard, over conversations that weren't enriched by the daily run, from the Backfill tab.

A **backfill** runs a prompt over a date range of conversations you already have, so they get the same Dimensions as the conversations a live integration brings in every day. You start one from the **Backfill** tab in the platform.

A backfill works for both [custom prompts](/dimensions/custom) and [standard Dimensions](/dimensions/standard).

## What a backfill does

1. Selects the conversations in the sources and date range you choose.
2. Runs the prompt on each of them.
3. Stores the labels.
4. Makes them available everywhere in the platform, including to the agent.

## When you need one

- You uploaded a file of conversations. Uploads are never enriched until you backfill them.
- You sent history through `/trackhistorical`.
- You created a new prompt and want it on the conversations you already have.
- You edited a prompt and want older conversations re-read with the new version.
- You want standard Dimensions on your data and daily enrichment isn't turned on for your workspace.

Conversations from a live integration are enriched every day without a backfill, for the prompts applied to that source. See [When enrichment runs](/dimensions/when-enrichment-runs).

## Run one

1. Save the prompt first. Every saved prompt, yours and the standard ones, is listed on the **Prompts** tab.
2. Open the **Backfill** tab.
3. Choose the prompt, the sources to apply it to, and the date range.
4. Start it. The **Backfill** tab shows its status and when it has finished.
5. Check coverage: ask the agent *"How many conversations from [start] to [end] on [source] have Dimensions from [prompt]?"*


The agent can design and save a prompt with you when Prompt Designer is turned on, but you start the backfill yourself on the **Backfill** tab.

For the full path from a new idea to two years of labeled history, see [Worked example: a competitor Dimension on two years of history](/dimensions/custom#worked-example-a-competitor-dimension-on-two-years-of-history).

## Things to know

- **How long it takes.** A backfill typically shows up within the hour, depending on how much data is being enriched. A long date range over a large source takes longer. Watch the status on the **Backfill** tab.
- **Session limit.** The **Session limit** field in Prompt Designer caps how many conversations a backfill processes each day, not in total: a limit of 2,000 means 2,000 a day. A large history at a low limit takes several days.
- **Prompts with a filter.** A prompt with a filter set in Prompt Designer doesn't run in the daily enrichment, so backfill it whenever you need new dates covered.
- **Backfills run in turn.** A long backfill can delay one started after it.
- **Check the date range.** A backfill only covers the dates you choose. Conversations outside them stay empty.
- **After editing a prompt,** backfill the same range again, then ask the agent to check that each conversation in the range has one row for the prompt.
- **Don't see the Backfill tab?** Email support@dimensionlabs.io to have it turned on for your workspace.