Know what every request costs,before you invoice for it.

Usage metering and billing ledgers for indie SaaS.

penrule · march ledger

Customers in the March ledger, with metered usage, draft invoice and state
Customer	Metered	Draft invoice	State
Hollowell Studios	142,330 min	$711.65	Review
Brackwater FM	61,240 min	$329.52	Review
Lantern Hour	18,904 min	$94.52	Approved
Marlow & Finch	18,402 min	$0.00	Drift

Model tokens API calls Audio minutes Seats GB-months Build minutes

Closing the books every month for small software companies like these.

Kettleby Lumaprint oxbow forms Saltmarsh brindle PARCHWORK

01How it works

No invoice leaves until the ledger balances.

Three moves, in the order your money moves. Click through them; each panel is the real screen you will use.

worker / transcribe.ts

Record a usage eventNode 18+, 2.1 kB

import { Penrule } from "@penrule/node";

const ledger = new Penrule(process.env.PENRULE_KEY);

// after a job finishes, once per job
await ledger.record({
  customer: "cus_brackwater",
  meter: "audio.minutes",
  quantity: 42.5,
  idempotencyKey: job.id,
});

Retries are safe: the idempotency key keeps a job from being counted twice.

Written to the ledgerlast 60 s

kettleby / reconciliation / 2026-03-31

Nightly run, March 3102:00 to 02:04 UTC

Meter	Metered	Priced	Delta
audio.minutes	412,880	412,880	0
diarized.minutes	18,402	0	18,402
storage.gb_months	1,204	1,204	0
seats	38	38	0

Suggested fixprice book v7

Add a rule for diarized.minutes and back-price this period. Based on your rate for audio.minutes plus your published diarization add-on.

diarized.minutes$0.0040 / min

Effective from2026-03-01

Recovered this period$73.61

Rules are versioned. Changing a price never rewrites past lines; it adds new ones.

kettleby / invoices / INV-2026-0318

KettlebyDraft INV-2026-0318
Period Mar 1 to Mar 31, 2026

Brackwater FMBilling contact: accounts@brackwater.fm
Net 14

Line	Qty	Amount
Audio transcriptionaudio.minutes at $0.0050	61,240	$306.20
Speaker diarizationdiarized.minutes at $0.0040	4,880	$19.52
Archive storagestorage.gb_months at $0.10	38	$3.80

Subtotal$329.52VAT 20%$65.90Total$395.42

Approval gate3 of 3 checks passed

Metered equals pricedAll 3 meters reconciled on Mar 31

Price book unchanged since last invoicev7, effective 2026-03-01

Within 15% of February$395.42 vs $361.08, up 9.5%

Approved and sent to your billing provider.

02The ledger

Built like a ledger, not a dashboard.

Price book

Tiers, minimums and per-seat rules, written down once.

First 50k minutes$0.0060

50k to 250k$0.0050

Above 250k$0.0035

Monthly minimum$29.00

Version 7, effective March 1

A cloth-bound ledger with an indigo spine and a fountain pen resting on a plaster shelf

Append-only

Nothing is edited. Corrections are new lines.

Each line is hash-chained to the one before it, so any number on an invoice traces back to the events that made it.

Drift checks

Undercharging shows up the next morning.

Marlow & Finch metered on a meter with no rule18,402 min, $73.61 unpriced

Greywater Pods still on the trial plantrial ended Mar 14

212 customers balancedchecked 02:04 UTC

Usage pages

Your customers see the numbers you see.

Brackwater FMApril, day 9 of 30

Transcription19,412 of 60,000 min

Diarization1,520 min

Storage39.2 GB

Exports

Approved drafts go wherever you already bill from.

A signed webhook, a REST endpoint and a nightly CSV. Penrule never charges a card; it hands your billing provider a number you have already checked.

webhookRESTCSVParquet

POST /hooks/penrule  invoice.approved
{
  "invoice": "INV-2026-0318",
  "customer": "cus_brackwater",
  "period": "2026-03",
  "total": 39542,
  "currency": "usd",
  "price_book": "v7",
  "ledger_head": "9f3c...e41a"
}

03Customers

Built for people who keep their own books.

Hanna Lindqvist, founder of Kettleby, at her desk in a brick studio with acoustic panels behind her

Kettleby, podcast transcription API

“We were giving away about three percent of our minutes and had no idea which customers it was.”

Hanna LindqvistFounder, Kettleby

Read Kettleby's story

40 minMonth-end close, down from two working days

$1,284Unbilled usage found in the first cycle

0Disputed invoices since moving in March

Portrait of Rohan Mehta — **Rohan Mehta**Founder, Lumaprint

Portrait of Adaeze Nwosu — **Adaeze Nwosu**CTO, Oxbow Forms

Portrait of Kenji Arai — **Kenji Arai**Co-founder, Saltmarsh Maps

04Compared

Three ways to meter usage.

Comparison of a month-end spreadsheet, an in-house metering system and Penrule
Criterion	Month-end spreadsheetWhat most of us start with	Built in-houseA table, a cron job, a weekend	PenruleA ledger for this one job
Where it shines	Familiar, free, endlessly flexible	Fits your stack and data model exactly	Metering, pricing and approval in one record
Time to a trusted invoice	Two days, every month	Six to ten weeks of build	One afternoon to instrument
Catches undercharging	Only if someone notices	If you write and maintain the checks	Nightly, per customer, per meter
Audit trail	Cell history, at best	Whatever you remembered to log	Append-only and hash-chained
Who maintains it	You, at every month-end	You, forever	We do, or you self-host the same code
Cost	Free, plus your evenings	About a quarter of an engineer	From $19 a month, flat

Build estimates come from our own first attempt in 2022, and from conversations with 31 teams who moved to Penrule.

05Pricing

One meter, three ways to run it.

Flat prices. We never take a percentage of what you bill.

Estimate your month

Drag to your expected volume. Overage is billed per 100k events, never per invoice.

Billable events per month2.4M

50k500k5M50M

Products to meter

2

Best fit

Studio

$49per month

Choose Studio

14-day trial on every plan, no card until your first approval Export the full ledger any time Prices in USD, excluding VAT

06Security

Your numbers stay yours.

Billing data is the most sensitive data a small company holds. We treat it that way, and we write down exactly how.

Read the security overview

Tamper-evident ledger

SHA-256 chain

Every line carries the hash of the line before it. A daily head hash is emailed to you, so you can prove nothing changed.

Pick where data lives

EU or US

Choose Frankfurt or Virginia when you create a workspace. Ledgers, backups and logs stay in that region.

Keys that can only write

scoped keys

Server keys can record events and nothing else. Reading invoices or changing prices needs a separate, rotatable key.

Self-host the same code

1 container

The Self-host license runs the exact build we run, as one container with Postgres. Your ledger never leaves your network.

07FAQ

Questions founders ask before switching.

Something missing? Write to us. A founder answers, usually the same day.

hello@penrule.app

08About

The four people behind Penrule talking around an oak table covered in printed spreadsheets — Graham, Priya, Kwame and Mei Lin in the Leeds office.

A small tool from a small team.

Two of us ran a usage-billed API for four years. On the last weekend of every month we exported logs, pasted them into a spreadsheet and hoped the formulas still matched the pricing page. They often did not.

Penrule is the tool we wanted then: a ledger that records every billable event once, prices it with a rule you can read, and refuses to invoice until the numbers agree. We are self-funded, we answer support ourselves, and we charge a flat price because metering software should not take a cut of your revenue.

2023Founded in Leeds

4People, no plans to be 40

Self-fundedNo investors to answer to

1 dayLongest support reply

Your first balanced ledger, this afternoon.

Fourteen days free on any plan. We only ask for a card after you approve your first real invoice.

Instrument one meter with a single call
Import your current pricing page as a price book
Reconcile last month before you trust this one

Create your workspaceStep 1 of 2

Work email Enter an email we can send your sign-in link to.

Product name Name the product so we can label your ledger.

Billable events per month Pick a range. A rough guess is fine.

Plan

Studio, billed monthly after your trial. Change plans any time.

Your workspace is ready.

We sent a sign-in link to your inbox. It expires in 15 minutes.

Install the SDK and record a first event See what shipped this month

What changed, line by line.

Every release, dated. We ship small changes most weeks and never change how past lines are priced.

Quickstart: a first balanced ledger.

About forty minutes from an empty workspace to an approved draft. You need a server-side key and one place in your code where billable work finishes.

01

Create a key

In Settings, API keys, create a write-only server key. It can record events and nothing else, so it is safe to keep in your worker environment as PENRULE_KEY.

02

Install the SDK

Official SDKs for Node and Python, or call the REST endpoint directly.

03

Record an event

Call record once per finished unit of work, with the customer ID you already use and a stable idempotency key. Penrule accepts events up to 35 days late and places them in the right period.

Quantities can be decimals; rounding happens at invoice time, per rule.
Unknown meters are accepted and flagged as drift, never dropped.

04

Add a price rule

Open Price book and describe each meter: a flat unit price, tiers, a monthly minimum or a per-seat fee. Import your public pricing page and Penrule drafts the rules for you to check.

05

Approve a draft

At period close, drafts appear in Invoices with three checks beside them. Approve one and it is sent to your billing provider by webhook. That is the whole loop.

Start a workspace or read the security overview.

How Kettleby stopped giving away three percent of its minutes.

A two-person transcription API, 214 podcast studios as customers, and a month-end spreadsheet that had quietly stopped matching the pricing page.

CompanyKettleby, Gothenburg

MetersAudio, diarization, storage

On Penrule sinceMarch 2026

Hanna Lindqvist, founder of Kettleby, holding a mug at her studio desk

Before

Kettleby bills podcast studios by the minute of audio it transcribes, with an add-on for speaker diarization and a small fee for archive storage. Hanna Lindqvist wrote the first billing script in an evening in 2023. By 2026 it was a spreadsheet, two scripts and a calendar reminder called "do the bills".

The pricing page had changed three times since. The spreadsheet had changed twice.

"Nobody was cheating anyone. We just could not say, for any single invoice, why it was that number."

The switch

Hanna added one record call at the end of each transcription job and imported the pricing page as a price book. Penrule drafted rules for audio and storage and flagged diarization as a meter with no rule at all.

Hands ticking a printed invoice draft with a fountain pen beside an open ledger — Kettleby still prints the first draft of each cycle and checks it by hand.

The first close

The first nightly reconciliation replayed February. It found 18,402 diarized minutes that had never been priced, and two studios still on a trial plan that had ended. Together that was $1,284 of usage nobody had billed.

Kettleby back-priced the current period only and wrote to the two studios before their next invoice. Neither objected; both asked for the usage page.

Now

Month-end takes about forty minutes: read the drafts, look at anything more than fifteen percent off last month, approve. There have been no disputed invoices since March.

Start your own ledger or go back to customers.

Security overview

How we store, protect and prove your billing data. Plain language first; the technical detail follows each point.

Last reviewed September 14, 2026

Ledger integrity

The ledger is append-only. Every line stores the SHA-256 hash of the previous line, and each night we email you the head hash. If a single historic line changed, every hash after it would stop matching.

Data and residency

You choose the EU (Frankfurt) or the US (Virginia) when creating a workspace. Ledgers, backups and logs stay in that region. Data is encrypted at rest with AES-256 and in transit with TLS 1.3.

Backups every six hours, kept for 35 days.
Full ledger export as CSV or Parquet at any time.
Deleted workspaces are purged from backups within 35 days.

Access

Server keys are write-only. Read keys and admin sessions are separate, scoped and rotatable. Workspace roles are owner, approver and viewer; only approvers can release a draft invoice.

Infrastructure

Penrule runs on a major cloud provider in two regions, with a transactional email provider for sign-in links and digests. We list every subprocessor in our privacy notice and give 30 days' notice before adding one.

Reporting an issue

Email security@penrule.app. We reply within one working day and credit researchers who ask to be credited.

Welcome back to the ledger.

We email you a one-time link. No passwords to keep, nothing to reset.

Check your inbox.

We sent a sign-in link. It works once and expires in 15 minutes.

Privacy notice

Effective June 1, 2026. Penrule Ltd, Leeds, United Kingdom.

What we collect

Account data (name, work email, company), billing data you send us as usage events, and basic service logs (IP address, user agent, request time). We do not use advertising cookies or third-party trackers on this site or in the app.

Why we collect it

To run the service you signed up for, to keep it secure and to send the emails you asked for. For usage events you are the controller and we are your processor; our data processing agreement applies automatically.

Who we share it with

Cloud hosting, in the region you choose.
A transactional email provider, for sign-in links and digests.
Our payment processor, for your own Penrule subscription only.

Your rights

You can access, export, correct or delete your data at any time from Settings, or by writing to privacy@penrule.app. We answer within 30 days, usually much sooner.

Terms of service

Effective June 1, 2026. A plain summary; the full agreement is sent with your first invoice.

The service

Penrule records usage events you send, prices them with rules you write and drafts invoices for you to approve. You are responsible for the prices you set and the invoices you approve; we are responsible for recording and computing them exactly as configured.

Paying us

Plans are billed monthly or yearly in advance; overage is billed monthly in arrears per 100,000 events. Self-host licenses are a one-time fee with a year of updates.

Your data

Your ledger is yours. You can export it in full at any time, including after you cancel, for 35 days.

Ending

Cancel from Settings at any time; the plan runs to the end of the period you paid for. We may end the agreement with 60 days' notice, or immediately for abuse of the service.

#/unknown

This page is not in the ledger.

The link may be old, or the page moved. Everything we publish is reachable from the home page.

Back to home Read the changelog

Know what every request costs,before you invoice for it.

No invoice leaves until the ledger balances.

Built like a ledger, not a dashboard.

Tiers, minimums and per-seat rules, written down once.

Nothing is edited. Corrections are new lines.

Undercharging shows up the next morning.

Your customers see the numbers you see.

Approved drafts go wherever you already bill from.

Built for people who keep their own books.

Three ways to meter usage.

One meter, three ways to run it.

Estimate your month

Your numbers stay yours.

Tamper-evident ledger

Pick where data lives

Keys that can only write

Self-host the same code

Questions founders ask before switching.

A small tool from a small team.

Your first balanced ledger, this afternoon.

Your workspace is ready.

What changed, line by line.

Nothing in the ledger matches that.

Quickstart: a first balanced ledger.

Create a key

Install the SDK

Record an event

Add a price rule

Approve a draft

How Kettleby stopped giving away three percent of its minutes.

Before

The switch

The first close

Now

Security overview

Ledger integrity

Data and residency

Access

Infrastructure

Reporting an issue

Welcome back to the ledger.

Check your inbox.

Privacy notice

What we collect

Why we collect it

Who we share it with

Your rights

Terms of service

The service

Paying us

Your data

Ending

This page is not in the ledger.