> ## Documentation Index
> Fetch the complete documentation index at: https://docs.blnkfinance.com/llms.txt
> Use this file to discover all available pages before exploring further.
# Rule Structure
> How Blnk Watch rules are structured and what each part of a rule does.
export const CtaCallout = props => {
const {title, buttonLabel, href, trackingEvent, buttonTarget, rel = "noopener noreferrer", children} = props;
const handleCtaClick = () => {
if (typeof window === "undefined" || !trackingEvent) {
return;
}
try {
window.dispatchEvent(new CustomEvent("blnk:docs-cta", {
detail: {
name: trackingEvent,
href
}
}));
} catch {}
try {
window.posthog?.capture?.(trackingEvent, {
href
});
} catch {}
const gaPayload = {
cta_href: href
};
try {
window.gtag?.("event", trackingEvent, gaPayload);
} catch {}
try {
window.dataLayer = window.dataLayer || [];
window.dataLayer.push({
event: trackingEvent,
...gaPayload
});
} catch {}
};
const isExternal = typeof href === "string" && (/^https?:\/\//i).test(href);
const target = buttonTarget ?? (isExternal ? "_blank" : undefined);
const linkRel = isExternal ? rel : undefined;
return ;
};
Blnk Watch is currently in beta. [Send us a message](mailto:support@blnkfinance.com)
Blnk Watch rules define how transactions are evaluated. Each rule describes a pattern to look for and what should happen when that pattern matches.
Rules operate only on **transactions**. They don't monitor balances, ledgers, or identities.
If you need extra business context (e.g. KYC tier, promo code), pass it on the transaction as `meta_data` and reference it in the rule.
***
## Watch scripts
Rules are written as **watch scripts**: plain-text files with the `.ws` extension.
Watch loads these scripts from a designated folder (by default `watch_scripts`), compiles them, and turns them into the rules that run against each transaction.
When you add or change a `.ws` file in that folder, Watch picks up the change and updates the active rule set.
Keep all watch scripts in that folder so Watch can find and load them.
For easier management, name files descriptively: camelCase or snake\_case both work (e.g. `HighValueUSD.ws`, `burst_to_same_destination.ws`).
That way you can tell what each script does from the filename alone.
***
## Rule anatomy
Every rule has two core parts: **when** (the pattern) and **then** (the outcome). The rest of this section walks through each piece and where to learn more.
A simple, complete rule looks like this:
```bash HighValueUSD.ws theme={"system"}
rule HighValueUSD { # Rule name
when amount > 4000 and currency == "USD" # Condition
then review # Verdict
score 0.5 # Score
reason "USD transaction exceeds 4,000" # Reason
}
```
| Part | What it does | Example |
| -------- | ------------------------------------------------------------------------------------- | ------------------------------------- |
| `rule` | Stable identifier for the rule; use a name that describes the pattern | `HighValueUSD` |
| `when` | Condition to look for in the transaction. | `amount > 4000 and currency == "USD"` |
| `then` | Outcome when the condition is met. | `review` |
| `score` | Rule-level risk weight; you define the scale. | `0.5` |
| `reason` | Human-readable explanation for why the rule triggered; used for debugging and audits. | `"USD transaction exceeds 4,000"` |
**Keep in mind:** When you need information that isn't part of the transaction payload, include it in `meta_data` first. A rule can use `meta_data.kyc_tier` or `meta_data.promo_code` only if your app sends those values with the transaction.
***
## Rule syntax
**First, you declare the rule.** The name after `rule` must be a single identifier in camelCase or snake\_case (e.g. `HighValueUSD`, `burst_to_same_destination`) and should describe the pattern or control so it’s clear in logs and audits.
```bash ruleName.ws {1} theme={"system"}
rule ruleName {
}
```
**Next, you define the condition.** Aim for one goal per rule: the condition should describe a single pattern or check. If you need to flag several different cases, use a separate rule for each so evaluation and debugging stay clear.
```bash ruleName.ws {2,3} theme={"system"}
rule ruleName {
when currency == "USD"
and amount > 4000
•••
}
```
**Then, you define the verdict** if the condition is triggered:
```bash ruleName.ws {5} theme={"system"}
rule ruleName {
when currency == "USD"
and amount > 4000
then review
•••
}
```
**Finally, you add more information about the verdict.** Score and reason are usually what the next part of your workflow uses: they tell you how serious the signal is and why the rule fired, so you know what to do with an alert from Watch.
```bash ruleName.ws {6,7} theme={"system"}
rule ruleName {
when currency == "USD"
and amount > 4000
then review
score 0.5
reason "USD transaction exceeds 4,000"
}
```
***
## Need help?
We are very happy to help you make the most of Blnk, regardless of whether it is your first time or you are switching from another tool.
To ask questions or discuss issues, please [contact us](mailto:support@blnkfinance.com) or [join our Discord community](https://discord.gg/7WNv94zPpx).
Sign up and manage your ledger with our back-office dashboard. You can invite teammates to collaborate and manage your ledger operations directly from the dashboard.