Ironfang Finance

E-invoice validation

Validate.
Understand. Fix.

Check UBL invoices and credit notes against EN 16931 and Peppol BIS Billing 3 rules. Find the failure, understand the rule and fix the source document.

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No account needed to try it. Anonymous XML and results are transient.

Ironfang Finance / validation resultExample output

invoice.xml

UBL Invoice / validation completed

Invalid

XML syntaxPassed

UBL schemaPassed

EN 169311 finding

Peppol rulesPassed

BR-CO-10

Line amounts do not add up

The document-level line total must match the sum of the individual line net amounts.

Read the rule explanation

Peppol BIS Billing 3Transient XML checks

Document validation

A clear path from XML to answers.

One validation result brings the document checks and rule findings together, with the detail you need to take the next step.

Invoices and credit notes

Check UBL Invoice and CreditNote XML against the supported Peppol BIS Billing 3 rulesets. Use the free browser tool or send a request from your application.

Every validation layer

See XML syntax, UBL schema, EN 16931 and Peppol rule results separately. Distinguish an invalid document from a validation service failure.

Findings you can act on

Read the rule identifier and finding, then follow a reviewed explanation where available. Fix the source document and validate it again.

Results you can keep

Download result JSON and a readable report. Signed-in and API results are saved for 30 days, with the option to delete them sooner.

Your first validation

From a finding to a fix.

Choose your document
Try the sample or upload invoice or credit note XML, up to 5 MiB. The free validator works without an account.
Read the findings
Follow the verdict through each validation layer. Open the available rule explanations to understand what needs to change.
Fix and validate again
Update your source document, rerun validation and download the results. Open the readable report to print or save it as a PDF.

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Try anonymously

Browser validation and JSON playground
Transient results
No signup required

Build with Ironfang Finance

API keys and saved validation history
Jobs, batches and webhooks
S3-compatible artifact delivery
SDKs, CLI and automation tooling

Try Ironfang Finance without an account. Create one when you're ready to integrate it. Free includes 250 validations each month; account generation requires a paid plan.

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Rule explanations

Understand what went wrong.

Start with the rule, follow its meaning and work back to your document. Explanations come from the same reviewed catalogue as the validator.

Browse the validation guide

BR-CO-10

Line amounts do not add up

The document-level line total must match the sum of the individual line net amounts.

BR-01

The specification identifier is missing

Invoice and CreditNote documents need a non-empty CustomizationID identifying their specification.

PEPPOL-EN16931-R004

Check the billing specification identifier

This rule checks the Peppol Billing identifier prefix and rejects a double-colon sequence in the identifier.

Other rules retain their engine finding and identifier. Explanations are shown where reviewed guidance is available.

Developer workflow

Make validation part of your application.

Send XML over HTTPS and receive structured results. List saved validations, read their findings and delete results through the same API.

Use the published Python or TypeScript validation SDK, Python CLI or GitHub Action. For durable work, configure signed webhooks and S3-compatible artifact delivery with independent retries. Delivery to your endpoint or bucket does not send an invoice over Peppol.

OpenAPI contract Integration examples

Ironfang Finance / API workflow

Required key scope:financewolf:einvoices:write

Request

curl --request POST 'https://api.ironfang.uk/financewolf/v1/einvoices/validate' \
  --header 'Authorization: Bearer YOUR_API_KEY' \
  --header 'Content-Type: application/xml' \
  --header 'Accept: application/json' \
  --header 'Idempotency-Key: invoice-2026-001' \
  --data-binary '@invoice.xml'

Example response - excerpt

200 OK

Content-Type: application/json

{
  "operation_id": "019f29a4-3158-7b81-8f64-f1072146de30",
  "status": "completed",
  "outcome": "valid",
  "ruleset": {
    "id": "fwrs_example_invoice_2026a"
  },
  "findings": [],
  "findings_summary": {
    "returned": 0, "total": 0,
    "cap": 1000, "truncated": false
  }
}

Send your XML file as the request body. The optional Idempotency-Key lets you retry the same request without a second validation or charge. Invalid documents also return 200, with outcome: invalid and their findings.

Required key scope:financewolf:einvoices:read

Request

curl 'https://api.ironfang.uk/financewolf/v1/einvoices/results' \
  --header 'Authorization: Bearer YOUR_API_KEY' \
  --header 'Accept: application/json'

Example response

200 OK

Content-Type: application/json
Cache-Control: no-store

{
  "results": [
    {
      "operation_id": "019f29a4-3158-7b81-8f64-f1072146de30",
      "outcome": "valid",
      "ruleset_id": "fwrs_example_invoice_2026a",
      "created_at": "2026-09-02T09:15:04Z",
      "expires_at": "2026-10-02T09:15:04Z",
      "available": true
    }
  ],
  "retention_days": 30
}

Returns up to 20 results, newest first. If next_cursor is returned, pass its value as ?before=NEXT_CURSOR to request the next page.

Illustrative responses. Authenticated results are saved for 30 days. Synchronous validation does not retain uploaded XML.

Pricing

Start free. Choose your document allowance.

Validate on Free, or subscribe to generate invoices and handle more documents. Fixed monthly prices in GBP, including applicable tax. No automatic overage charges.

Free

£0/ month

250 validations / month

Validate documents
Saved results and API access
No card required

Start free

Build

£29/ month

5,000 operations / month

Validate and generate documents
Saved results and API access
One shared document allowance

Start with Build

Pro

£99/ month

25,000 operations / month

Validate and generate documents
Saved results and API access
One shared document allowance

Start with Pro

Platform

£299/ month

100,000 operations / month

Validate and generate documents
Saved results and API access
One shared document allowance

Start with Platform

How your allowance works

One completed validation counts, including a result that finds invoice errors. One successful generation counts once. Downloads and idempotent retries add no usage. Malformed requests and service failures do not use your allowance; unfinished work reserves it.

Free resets each UTC calendar month. Paid allowances follow your monthly subscription period. Account-based generation requires a paid plan. The anonymous validator and JSON playground remain free with request and rate limits.

For UK and EU businesses

Paid plans are available to businesses and sole traders established in the UK or EU. UK businesses do not need a VAT number. EU automatic checkout requires a verified VAT number and matching business details. EU businesses without a VAT number, or with verified details that need review, must be approved before paying.

Enter your business details and request any required review in the billing portal. You choose your subscription explicitly. Manage plan changes and cancellation there too; Ironfang Finance has separate payment details and invoice history.

See our terms and refund policy. Document validation and generation do not send invoices over Peppol or certify legal or tax compliance.

Questions

Know what your result means.

Do I need an account to try it?: No. The free Peppol validator accepts a sample or your own XML without an account. Create an account when you want saved validation history and API integration.
When do I need a paid plan?: Free accounts include 250 validations per UTC calendar month. Choose Build, Pro or Platform to generate documents through your account or increase your allowance. Anonymous browser tools remain free with request and rate limits.
Will I be charged if I reach my allowance?: There are no automatic overage charges. New account operations stop at the allowance until capacity is released, the period renews or you upgrade. Existing results stay available within their retention period. Subscriptions renew monthly until cancelled.
What happens to my invoice XML?: Synchronous validation does not retain uploaded XML. Anonymous results are transient; authenticated result JSON and findings are retained for 30 days and can be deleted sooner. Durable API jobs, when enabled, temporarily retain encrypted input until completion, cancellation or 24-hour expiry cleanup.
Can I download the result?: Yes. Download JSON and an unsigned readable report. The report can be printed or saved as a PDF from your browser. Downloaded copies stay under your control.
Does a passing result send or certify my invoice?: No. Validation checks supported structured-document rules. It does not send invoices over Peppol, establish participant registration or certify legal or tax compliance.

Less to operate. More to ship.

Start with one document.

Try the sample, understand the findings and bring validation into your workflow.

Try the free validator Create a free account

No card required for a Free account. Start with 250 validations per UTC calendar month and upgrade when you need more.

Validate.Understand. Fix.

A clear path from XML to answers.

Invoices and credit notes

Every validation layer

Findings you can act on

Results you can keep

From a finding to a fix.

Choose your document

Read the findings

Fix and validate again

Try anonymously

Build with Ironfang Finance

Understand what went wrong.

Line amounts do not add up

The specification identifier is missing

Check the billing specification identifier

Make validation part of your application.

Request

Example response - excerpt

Request

Example response

Start free. Choose your document allowance.

Free

Build

Pro

Platform

How your allowance works

For UK and EU businesses

Know what your result means.

Start with one document.

Validate.
Understand. Fix.