---
title: "The first preview, in seconds"
description: "A preview runs a definition over the record before anything is spent. It runs the same predicate that the monitor will run, and it returns a count, the coverage and the population in seconds."
section: start
address: /start/the-first-preview
contract: 0476e35e6e275db5
---

# The first preview, in seconds

A preview runs a definition over the record before anything is spent. It runs the same predicate that the monitor will run, and it returns a count, the coverage and the population in seconds.

[figure: The preview runs the same predicate that the monitor will run, once, over the record that the platform already holds.]

A strategist first asks whether a definition is any good, before asking who the leads are. The preview returns that answer in seconds. It runs over the record that the platform already holds, before you arm a monitor and before you spend anything.

## Definition

A definition is a predicate in the closed language of the platform. It states who (a population of companies or people), what (conditions on their facts and signals), and when (a window). You write a definition in the definitions studio or in the composer, or the agent writes it. The object is the same in all three places. A monitor runs a definition on every beat, and a preview runs it once.

## Preview result

| part | meaning |
|---|---|
| the count | how many units of the population match today |
| the coverage | how much of the population the record has read, by source and by channel, which shows whether a small count comes from few matches or from a thin record |
| the population | the population that the preview ran over, with its size |
| the basis | for every number, whether the platform observed it, a source stated it, a rule derived it, or the platform estimated it with an interval |

The preview keeps *never measured* apart from *empty*. A population that nobody has read returns *never measured*, not zero. A good definition therefore does not look bad when the record is thin.

## Preview call





```sh
curl -X POST https://api.scaleintelligence.co/v1/ask/preview \
  -H "Scale-Key: $SCALE_KEY" -H "Scale-Scope: tenant/<id>/brand/<id>" \
  -H "content-type: application/json" \
  -d '{ "predicate": { "…": "the definition's tree" } }'
```




```typescript
import { client } from "@scale/sdk";
const preview = await client.ask.preview({ predicate: tree });
// preview.body holds the count, the coverage and the population, each number with its basis.
```




The [preview's reference page](/reference/ask/preview) shows the full shape of the input and of the result. The agent calls the same route when it proposes a definition, reads the yield, revises the definition and converges on it. The composer calls the same route too, so both use one implementation.