---
title: "Monitors"
description: "Generate issues and trigger alerts by creating custom monitors to track errors, performance, and metrics."
url: https://docs.sentry.io/product/monitors-and-alerts/monitors/
---

# Monitors

Sentry's Monitors are used to customize when to turn errors and performance problems into issues. They can be configured using conditional rules to create issues when specific criteria are met. For example, you could monitor when the duration of a transaction takes longer than 3 seconds on a particular browser. Further automate your issue creation experience using Monitors to automatically add assignees and set different priorities based on severity.

## [Types of Monitors](https://docs.sentry.io/product/monitors-and-alerts/monitors.md#types-of-monitors)

### [Custom Monitors](https://docs.sentry.io/product/monitors-and-alerts/monitors.md#custom-monitors)

You can use Custom Monitors to track thresholds on errors, spans, logs, releases, and application metrics, the size of mobile app builds, the uptime and performance of any scheduled, recurring job, or the uptime and performance of any HTTP request.

* [Metric Monitors](https://docs.sentry.io/product/monitors-and-alerts/monitors.md#metric-monitor-settings): Track thresholds on errors, spans, logs, releases, and application metrics.
* [Mobile Builds Monitors](https://docs.sentry.io/product/monitors-and-alerts/monitors.md#mobile-builds-monitor-settings): Track the size of mobile app builds.
* [Cron Monitors](https://docs.sentry.io/product/monitors-and-alerts/monitors/crons.md): Track the uptime and performance of any scheduled, recurring job.
* [Uptime Monitors](https://docs.sentry.io/product/monitors-and-alerts/monitors/uptime-monitoring.md): Track the uptime and performance of any HTTP request.

### [Default Monitors](https://docs.sentry.io/product/monitors-and-alerts/monitors.md#default-monitors)

Sentry also provides default monitors that are automatically created for you when you create a new project.

* **Issue Stream Monitor**: The default monitor tracking new issues of all types created for a project, including issue types that may not have a dedicated Monitor detecting them (ex. Replay issues)
* **Error Monitor**: The default monitor based on [issue grouping/fingerprint rules](https://docs.sentry.io/concepts/data-management/event-grouping.md)

## [Creating a Monitor](https://docs.sentry.io/product/monitors-and-alerts/monitors.md#creating-a-monitor)

To create a Monitor, navigate to the [Monitors](https://sentry.io/monitors/new/) page and click **Create Monitor**. You can choose between the three types of Monitors (metric, cron, and uptime). Each one will have a separate configuration process.

You can also create a Metric Monitor directly from a query:

* From the [Application Metrics](https://docs.sentry.io/product/explore/metrics.md) Explorer, open the **Save As** menu and choose **Monitor for** to create a Monitor with the current metric and filters pre-selected.
* From [Discover](https://docs.sentry.io/product/explore/discover-queries.md), use the **Create Monitor** button to turn the current query into a Monitor.

### [General Settings](https://docs.sentry.io/product/monitors-and-alerts/monitors.md#general-settings)

Monitors are made of attributes that define when to create an issue, and actions that define what to do when an issue is created.

* Name the Monitor
* Select the project, and in some cases, the environment
* Select attributes based on the Monitor type
* Set priority based on attributes
* Set auto-resolve based on attributes
* Set the assignee
* Connect [Custom Alerts](https://docs.sentry.io/product/monitors-and-alerts/alerts.md) like external notifications and ticket creation to pair with your Monitor

Assignees set by [ownership rules](https://docs.sentry.io/product/issues/ownership-rules.md) will override assignees set by Monitors.

### [Metric Monitor Settings](https://docs.sentry.io/product/monitors-and-alerts/monitors.md#metric-monitor-settings)

Metric Monitors are used to track thresholds on data from errors, spans, logs, releases, and application metrics.

Choose the dataset and metric, the interval for how often to check, and the way you want to monitor for changes. You can choose an absolute number threshold, a percentage change, or dynamic anomaly detection.

#### [Issue Detection Settings](https://docs.sentry.io/product/monitors-and-alerts/monitors.md#issue-detection-settings)

**Fixed Thresholds**

When setting an absolute number threshold, a percentage change, or dynamic anomaly detection, here are a few considerations: Use a fixed threshold or a percentage change threshold when you have a clear idea of what constitutes good or bad performance. Here are some examples:

* When your app's crash rate exceeds 1%
* When your app's transaction volume drops to zero
* When any issue affects more than 100 enterprise users in a day
* When the response time of a key transaction exceeds 500 ms

**Dynamic Thresholds**

Dynamic thresholds help you detect when a metric deviates significantly from its “normal” range. For example, the percentage of sessions affected by an issue in the last 24 hours is *20% greater than one week ago*, rather than the percentage of sessions affected is simply *greater than 20%*, which would be a fixed threshold.

Dynamic thresholds are good for when it’s cumbersome to create fixed thresholds for every metric of interest, or when you don’t have an expected value for a metric, such as in the following scenarios:

* **Seasonal fluctuations**: Seasonal metrics, such as number of transactions, are more accurately monitored by comparing them to the previous day or week, rather than a fixed value.
* **Unpredictable growth**: Fixed-threshold alerts may require continuous manual adjustment as traffic patterns change, such as with a fast-growing app. Dynamic thresholds work regardless of changing traffic patterns.

### [Mobile Builds Monitor Settings](https://docs.sentry.io/product/monitors-and-alerts/monitors.md#mobile-builds-monitor-settings)

Mobile Builds Monitors track the size of your iOS or Android app across builds. Monitors help alert and enforce thresholds on cadenced uploads, such app store releases or nightlies. See [Size Analysis docs](https://docs.sentry.io/product/size-analysis.md) to learn how to upload builds.

#### [Threshold Types](https://docs.sentry.io/product/monitors-and-alerts/monitors.md#threshold-types)

There are three threshold types for Mobile Builds:

* **Absolute Size**: Fail if size exceeds threshold (e.g., max 50 MB)
* **Absolute Diff**: Fail if size increases by more than threshold (e.g., max 5 MB increase)
* **Relative Diff**: Fail if size increases by more than threshold percentage (e.g., max 10% increase)

For any of these threshold types, you can monitor Install/Uncompressed Size or Download Size and filter to a specific subset of builds.

If you choose either of the diff thresholds, the baseline build is the most recent build that matches:

* `platform` (iOS or Android)
* `package_name` (e.g., `com.example.app`)
* `build_configuration` (e.g., `Release`)
* any additional filters you set on the monitor

### [Cron Monitor Settings](https://docs.sentry.io/product/monitors-and-alerts/monitors.md#cron-monitor-settings)

Cron Monitors are used to track the uptime and performance of any scheduled, recurring job.

Choose the schedule for how often to check, set the check-in margin, the max runtime, and failure tolerance. Learn how to set up a [Cron Monitor](https://docs.sentry.io/product/monitors-and-alerts/monitors/crons/getting-started.md).

### [Uptime Monitor Settings](https://docs.sentry.io/product/monitors-and-alerts/monitors.md#uptime-monitor-settings)

Uptime Monitors are used to track the uptime and performance of any HTTP request.

Choose the URL and HTTP request you wish to monitor. Set the interval, timeout, any headers you wish to include, and failure tolerance. Learn how to set up an [Uptime Monitor](https://docs.sentry.io/product/monitors-and-alerts/monitors/uptime-monitoring.md).

## [Managing Monitors](https://docs.sentry.io/product/monitors-and-alerts/monitors.md#managing-monitors)

You can see a list of all your Monitors on the [Monitors](https://sentry.io/monitors/) page. Select a Monitor type at the top of the page to narrow down the list. By default, Monitors are filtered down to your projects.

Monitors are a Project-level feature, but the permission set is organization-level. By default, all members can create and edit Monitors. You can update this setting in [Organization Membership settings](https://sentry.io/settings/organization/).

By clicking on a Monitor, you can view the details, edit the Monitor, or disable it.

The details page will show a high level chart of the Monitor's performance, the configuration, created issue, and connected automations.

## Pages in this section

- [Cron Monitoring](https://docs.sentry.io/product/monitors-and-alerts/monitors/crons.md)
- [Uptime Monitoring](https://docs.sentry.io/product/monitors-and-alerts/monitors/uptime-monitoring.md)