> For the complete documentation index, see [llms.txt](https://kb.bravegen.com/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://kb.bravegen.com/carbon/core-concepts/inventory-items/inventory-rules.md).

# Inventory Rules

How rules connect an activity source to the inventory items that report its emissions.

A **Rule** connects an [Activity Source](https://kb.bravegen.com/carbon/core-concepts/activity-sources) to the Inventory Items that report its emissions.

A Rule holds no emission factor, calculation, or reporting category of its own. It decides which [Inventory Item Templates](https://kb.bravegen.com/carbon/core-concepts/inventory-items/inventory-templates) apply to a source, and therefore which emissions boundaries are reported from that activity.

Rules are managed under **Settings** → **Rules**.

### What a rule does

* Defines the **Restrictions** that determine which sources the rule can be assigned to
* References one or more Inventory Item Templates
* Creates and governs the Inventory Items on every source it is assigned to

### How rules fit together

1. A **Template** defines the calculation and reporting setup.
2. A **Rule** references one or more templates.
3. The Rule is assigned to an Activity Source at an entity during [**Task Review**](https://kb.bravegen.com/carbon/core-concepts/data-collection/tasks/task-reviews).
4. That assignment creates one Inventory Item per referenced template.

{% hint style="info" %}
One Rule can produce several Inventory Items from a single source. An electricity rule might reference four templates — location based consumption, market based consumption, well-to-tank losses, and transmission & distribution losses — so one meter reading fans out into four reportable lines without double counting.
{% endhint %}

### Restrictions

Restrictions are matching criteria checked against the source. Only rules whose restrictions match are offered in the rule selection input during Task Review.

| Field                    | Description                                                                                                                                                                                                                                          |
| ------------------------ | ---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- |
| **Source Activity Unit** | The unit the incoming activity data arrives in. The rule is only suggested for sources with this unit, and it sets the incoming unit for every template attached to the rule. This is set when the rule is created and cannot be changed afterwards. |
| **Supplier**             | Restricts the rule to sources from one or more suppliers. Leave as **Any Supplier** to match regardless of supplier.                                                                                                                                 |
| **Source Identifiers**   | Restricts the rule to sources carrying specific identifiers, such as ICP or NMI numbers. Leave as **Any Identifiers** to match any.                                                                                                                  |

Leave a restriction empty to make it broader. A rule with no supplier or identifier restriction is suggested for every source matching the activity unit.

Select **+** beside **Source Activity Unit** or **Supplier** to add a unit of measure or supplier that does not exist yet, without leaving the rule.

{% hint style="info" %}
**Source Activity Unit** is immutable. To report the same activity in a different unit, create a new rule for that unit — or convert the incoming data with a unit conversion step on the template.
{% endhint %}

{% hint style="info" %}
If an expected rule doesn't appear during Task Review, check its restrictions against the source's unit of measure, supplier, and identifiers. A mismatch on any one of them hides the rule from selection.
{% endhint %}

### Attaching inventory item templates

The **Inventory Item Templates** panel lists every template the rule applies. Use **Add Inventory Template** to attach an existing template, or create a new one from the same input.

Selecting a template in the list opens **Edit Template**, where you configure the emission factor group, calculation steps, and reporting categorisation. These are the same fields described in [Inventory Items](https://kb.bravegen.com/carbon/core-concepts/inventory-items).

**Rules using this** shows every other rule that references the selected template.

{% hint style="warning" %}
Templates are shared. Editing a template from inside one rule changes every Inventory Item created by every rule that references it, and can alter historical totals and disclosures. Check **Rules using this** before you change an emission factor group, calculation, or framework mapping.
{% endhint %}

A template's **Source Unit of Measure** comes from the rule's **Source Activity Unit**. Where the emission factor is defined in a different unit, add a unit conversion or calculation step to the template — for example, converting `GWh` to `kWh` before applying a factor defined in `kWh`.

### Create a rule

In **Settings** → **Rules**, select **New Rule**.

| Field                   | Description                                                                                                                                                         |
| ----------------------- | ------------------------------------------------------------------------------------------------------------------------------------------------------------------- |
| **Name**                | A unique name for the rule. Use something that identifies the activity and the supplier or boundary it covers, for example `Greenpower Electricity Unknown Losses`. |
| **Description**         | Required. Describes the type of activity this rule is suggested for, for example `Electricity consumption supplied by Green Power`.                                 |
| **Restrictions**        | The matching criteria described above.                                                                                                                              |
| **Inventory Templates** | One or more templates to apply. Add at least one, unless the source should collect activity data without producing emissions.                                       |

Select **Create** to save the rule. It is then available for selection on any matching source.

### Create a rule during task review

You do not need to build rules in advance. At the **New Inventory Items** step of [Task Review](https://kb.bravegen.com/carbon/core-concepts/data-collection/tasks/task-reviews), select **new rule** from the rule selection input, choose an emission factor for the source, and give the rule a name.

BraveGen Carbon creates the rule and an inventory item template with suggested GHG categorisation. Review it afterwards from **Settings** → **Rules**, or from the rule link on the newly created source.

### Sources that should not calculate emissions

Set the inventory rule to **none** where activity is collected for calculation or BI purposes only. See [Metric Sources](https://kb.bravegen.com/carbon/core-concepts/activity-sources/metric-sources) for reporting metric activity without producing emissions.

### The default spend rule

Sources with a currency unit of measure are assigned the ✨ **spend-based** rule by default. This rule bypasses inventory item templates and creates the Inventory Item directly from transaction and supplier data. See [Spend Based Inventory](https://kb.bravegen.com/carbon/core-concepts/inventory-items/spend-based-inventory).

### Reviewing and maintaining a rule

Each rule has three tabs:

| Tab                 | Description                                                         |
| ------------------- | ------------------------------------------------------------------- |
| **Rule**            | The rule's name, description, restrictions, and attached templates. |
| **Inventory Items** | Every Inventory Item created by this rule, across all entities.     |
| **Log**             | The rule's change history.                                          |

Check the **Inventory Items** tab before changing a rule. It shows the reporting reach of the change.

To apply a variation of an existing rule — a different supplier, or one extra boundary — duplicate the rule rather than editing the original, so existing Inventory Items keep their current configuration. Duplicating is also how you handle a change of activity unit, since **Source Activity Unit** cannot be edited after creation.

{% hint style="warning" %}
Removing a template from a rule, or archiving the rule itself, deletes or archives the Inventory Items created from it. Those items stop contributing to reporting at every entity the rule is assigned to. Check the **Inventory Items** tab first, and confirm the impact on historical totals and disclosures before you proceed.
{% endhint %}

### Permissions

Only Administrators can create and update Inventory Rules and Inventory Item Templates. See [User Roles](https://kb.bravegen.com/carbon/configuration/user-management/user-roles).

### Summary

* A Rule connects an Activity Source to one or more Inventory Item Templates.
* Restrictions control which sources the rule is suggested for during Task Review.
* Each attached template produces one Inventory Item per source.
* Templates are shared across rules — edits propagate everywhere they are referenced.
* Removing a template, or archiving a rule, removes the Inventory Items it created.
* Currency-based sources use the default spend rule, which bypasses templates.