> **Source:** https://knowledge.leegality.com/document-execution/workflows/v4/rule-engine/how-to/validate-before-proceed
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---
# Validate fields before Proceed

**Goal:** the workflow must not move past a stage while the data is wrong — and the person running it should be told exactly what to fix. Working example: *every document's IRN must be filled and follow the format `LOAN-123456`; if not, Proceed is blocked and the error names the offending document.*

This is a [validation rule](https://knowledge.leegality.com/document-execution/workflows/v4/rule-engine/rule-categories#validation-rules): it runs on a stage's **Proceed**, checks a condition, and raises an error that blocks the stage. Validation is also how "make X mandatory" asks usually ship — this page covers the general pattern, including format checks and checks across *every* item.

## The spec

```
TARGET field:   IRN, on every document (including documents added at run time)
ACTION:         Validate at Proceed (block with error)
SUBJECT field:  IRN of each document
CONDITION:      IRN missing, or IRN not matching ^LOAN-[0-9]{6}$
OUTCOME:        Proceed on the Create stage is blocked with
                "IRN is mandatory for document N" or
                "IRN in document N must follow the format: LOAN-123456";
                with all IRNs valid, Proceed goes through
Workflow:       (yours)
```

Note the spec includes the **error messages word for word** — for validation rules, the message is part of the requirement.

## The rule logic

```
#version 2.0
var curDoc = 1; for(doc in documents) { var irn = doc.irn; if(irn != null) { irn = trim(irn); } if(irn == null || isEmpty(irn)) { throw "IRN is mandatory for document " + curDoc; } else { if(regex(irn, "^LOAN-[0-9]{6}$") == false) { throw "IRN in document " + curDoc + " must follow the format: LOAN-123456"; } } curDoc = curDoc + 1; }
```

Three habits of a good validation rule, all visible here:

- **It loops over everything.** `for(doc in documents)` checks every document — including ones the runner adds on the fly — instead of hardcoding "document 1".
- **It counts like a human.** `curDoc` starts at 1, so the error says "document 2", never "index 1".
- **It layers the checks.** Missing first, then format — the runner gets the most fundamental problem first. One behaviour to know: the rule stops at the **first** offending document per attempt. Fix it, Proceed again, and the next problem (if any) surfaces. That's standard for validations; a single error listing *all* offenders at once is possible in the rule language — ask Support or see Advanced: LEEQL.

## Adapt these parts

| Part | In the logic | Change it to |
| --- | --- | --- |
| What's checked | `doc.irn` | The field to validate (for a pack-level custom field, drop the loop and read `pack.lecf_yourField`) |
| The format | `"^LOAN-[0-9]{6}$"` | Your regex — anchored with `^` and `$` so the whole value must match |
| Error messages | both `throw` strings | Your exact messages, with the 1-based document number kept in |

## Configure it

1. Rule Engine panel → new rule → **Rule Title**: `IRN mandatory + format on all documents`.
2. Paste the adapted logic into **Create Rule**.
3. **Trigger Method**: **On Proceed Create** — documents and their IRNs live in the Create stage, so that's the Proceed to guard. Validating invitee data instead? Same pattern, **On Proceed Invitee**.
4. Save. Full configuration flow: [Build your first rule](https://knowledge.leegality.com/document-execution/workflows/v4/rule-engine/build-your-first-rule).

## Test it — all three states

1. Leave document 2's IRN empty, Proceed → blocked: *IRN is mandatory for document 2*.
2. Fill it with `LOAN-12` (too short), Proceed → blocked: *IRN in document 2 must follow the format: LOAN-123456*.
3. Fill it with `LOAN-123456`, Proceed → goes through.
4. Add a new document at run time with no IRN, Proceed → blocked again — the loop catches runtime additions too.

## Related

The conditional variant — mandatory only when another field says so — is [Make a field mandatory with a rule](https://knowledge.leegality.com/document-execution/workflows/v4/rule-engine/how-to/make-a-field-mandatory). Simple format checks on a single field can also be done without a rule at all, via the field's [Validations](https://knowledge.leegality.com/document-execution/workflows/v4/setup-configuration/field-configuration) tab; use a rule when the check is conditional, spans many items, or needs a custom message.