What’s the Difference Between SLAs, SLOs and SLIs?

Last updated: September 2026

Service level agreements (SLAs) are the external promises you make to customers. Service level objectives (SLOs) are the internal reliability targets your team sets to keep those promises. Service level indicators (SLIs) are the measurements that prove whether you’re hitting them. Together, the three connect customer expectations to day-to-day monitoring, alerting, and incident response, and getting that connection right matters. PagerDuty’s 2026 State of AI-First Operations report found that more than two-thirds of organizations lose more than $300,000 per hour during an IT incident, with 8% losing over $1 million per hour. SLOs tell you, in real time, how close you are to breaking a customer promise and how urgently to respond.

Key takeaways

• An SLA defines a contractual or business commitment to a customer.
• An SLO defines the reliability target a service team aims to meet.
• An SLI measures actual service performance against that target.
• Teams use SLO tracking to detect user impact, prioritize incidents, guide escalation, and support post-incident learning.
• Error-budget and burn-rate signals help teams focus response on incidents that actually threaten reliability commitments, not every metric blip.

What’s the relationship between SLAs, SLOs, and SLIs?

SLAs, SLOs, and SLIs form a hierarchy: an SLA can contain several SLOs, and each SLO depends on one or more SLIs for measurement.

Here’s how the three work together in practice:

1. A customer agreement promises 99.99% monthly availability (the SLA).
2. The service team sets a 99.99% availability SLO to support that promise.
3. The team measures successful requests against total valid requests as the SLI.
4. An alert triggers when the service consumes its error budget too quickly.

What is a service level agreement (SLA)?

An SLA is an agreement between a company and its customers that defines specific service commitments, such as availability, response time, or support response, and what happens if those commitments aren’t met.

SLAs can also define:

• Support response or resolution times
• Scheduled maintenance rules
• Service credits or other remedies
• Incident communication responsibilities
• Scope and exclusions for the commitment

Common SLA challenges

Business or legal teams often write SLAs without enough input from technical teams. That gap can produce commitments that omit important service conditions or rely on metrics engineers can’t measure consistently. The mismatch usually shows up during the incident, not before it.

Business, legal, and technical teams should define an SLA together and confirm every commitment has:

• A clearly defined metric
• A measurement method
• A time window
• A realistic target
• A process for reporting breaches

When should a team use an SLA?

SLAs are most common between vendors and paying customers. A free-to-use service may not need a formal SLA, though the team can still use SLOs to set internal reliability expectations.

What is a service level objective (SLO)?

An SLO is a reliability target for a specific service metric: the internal bar a team holds itself to, whether or not a formal SLA exists.

A complete SLO includes:

• Metric: what the team measures
• Target: the required level of performance
• Time window: the period used for evaluation

For example: “The checkout service will complete at least 99.9% of valid requests successfully over a rolling 30-day period.”

SLOs can measure several aspects of the user experience:

A useful SLO reflects the lowest acceptable reliability level for the service, set with input from customer needs, business impact, technical constraints, and historical performance, not just what’s easiest to collect. CPU usage, memory usage, and host availability can help diagnose a problem, but they rarely show whether a customer could actually complete an important action. A user-centered SLI, such as successful payment completion, page load latency, or valid API responses, should lead. Infrastructure metrics help explain why that SLI moved.

SLO design principles

SLOs should stay:

• Simple
• Clearly defined
• User-centered
• Easy to measure
• Linked to a specific owner
• Limited to metrics that can actually change an operational decision

How do teams monitor SLOs during incident management?

Effective SLO monitoring connects live SLI data directly to the incident response workflow, rather than living in a separate dashboard.

1. Select user-centered SLIs that represent availability, latency, errors, or another important user journey.
2. Set a target and time window for expected performance.
3. Track the current SLI against that target continuously.
4. Measure error-budget consumption: how much allowed unreliability the service has used.
5. Alert on actionable risk: when the SLO is breached or the burn rate shows a breach is likely.
6. Route the alert to the right responder based on service ownership and severity.
7. Review the result against incident timelines, customer reports, and response metrics.

Error budgets and burn rate

The burn rate shows how quickly a service is consuming its error budget. A normal rate may just need observation, while a rapid rate signals an active incident or a risky change.

Teams use burn-rate signals to:

• Raise the priority of an incident consuming budget quickly
• Escalate to additional responders as customer impact grows
• Pause risky releases or nonessential changes
• Redirect engineering time toward reliability work
• Resume normal delivery once the service recovers

Burn-rate alerting lets teams respond to actual impact instead of paging on every isolated metric change, which matters given how much toil noisy alerting creates. PagerDuty reduces alert noise by up to 91%, according to a Forrester Total Economic Impact™ study, and AIOps customers see 30% faster incident resolution as a result.

How are SLAs and SLOs different?

SLAs define external commitments between a company and its customers; SLOs define the internal targets that help teams meet those commitments.

When an SLO falls below target, the team should investigate and respond before the SLA is breached. The SLI is the evidence that shows whether the SLO is still on track.

What is a service level indicator (SLI)?

An SLI is the measured value of a service metric: the actual number that shows how the service performed during a specific period.

For an availability SLO, teams typically calculate the SLI as:

SLI = successful valid requests ÷ total valid requests × 100

A practical SLO tracking example might look like this:

The SLI value alone doesn’t determine incident priority. Teams should also weigh the affected user journey, the number of customers affected, the duration, and the rate of error-budget consumption.

SLI selection challenges

Tracking too many indicators creates extra work and can increase alert noise. Start with a small set of SLIs that represent the most important user journeys. Each SLI should have:

• A clear definition of valid and invalid requests
• A reliable data source
• A known owner
• A defined calculation method
• A documented response for when performance falls below the SLO

SLIs stay useful when they help a team make a decision. Diagnostic metrics can support investigation without becoming separate paging signals.

When are SLIs necessary?

SLIs are essential whenever a team needs to measure performance against an SLO. Without one, a team can’t determine whether the service is meeting its target, or how large and how long a reliability problem has been.

How do SLOs support the incident lifecycle?

SLO tracking should inform every stage of incident management, from preparation through post-incident review, not just the alerting moment.

Preparation

Before an incident occurs, teams should:

• Define SLOs for critical services and user journeys
• Assign owners for each SLO
• Document error-budget policies
• Set severity and escalation rules
• Test alert routing and responder coverage
• Establish a baseline for normal SLI performance

Detection

During detection, correlate SLI changes with other signals: logs, health checks, synthetic tests, customer reports. Alerts should focus on sustained user impact or rapid burn, not every short-lived threshold violation. A good alert identifies:

• The affected service
• The SLO and SLI involved
• The current value
• The target and time window
• The estimated error-budget impact
• The responder or team responsible for action

Response

SLO and burn-rate data help responders determine urgency: a fast burn rate, a critical user journey, or a broad availability failure can justify higher severity and wider escalation. SLO context in the incident record helps responders decide whether to roll back a change, divert traffic, disable a feature, or pursue another mitigation.

Recovery

Responders should confirm the SLI has returned to an acceptable level and the service continues to meet the SLO, checking the affected user journey, dependencies, and error-budget trend.

Post-incident learning

After an incident, compare the SLI timeline against incident start and recovery times, customer reports, detection and acknowledgement times, escalations, changes or deployments, and error-budget consumption. The review may show the SLI missed a customer-impacting failure, alerted too late, or generated noise without an actionable response. When that happens, revise the SLI, SLO, alert threshold, runbook, or ownership model.

What are best practices for SLO tracking in incident workflows?

Effective SLO tracking ties every target to a real user outcome, keeps the alerting surface small, and routes context, not just noise, to the responder.

• Tie every SLO to a user outcome or business-critical service.
• Keep the initial set small enough for teams to maintain.
• Define realistic targets with both business and technical stakeholders.
• Use rolling or calendar-based time windows consistently.
• Alert on sustained SLO risk, error-budget consumption, or burn rate.
• Include the SLO target, current SLI, and time window in every alert.
• Route alerts through the team’s on-call and escalation process.
• Use automation for safe diagnostics, enrichment, rollback, or remediation.
• Record incident annotations so teams can compare SLO changes with deployments and other events.
• Review SLOs after major incidents, product changes, and shifts in customer expectations.

Automation is what makes this list sustainable rather than aspirational. Manual incident response costs organizations $30.4 million a year on average, versus $16.8 million for teams running automated response, according to PagerDuty’s Automation Survey Whitepaper of 500 IT leaders, nearly a 2x gap.

Human responders should still determine severity and approve any action carrying material risk, but enrichment, correlation, and safe remediation don’t need to wait on a person.

Which metrics should teams track alongside SLO performance?

SLO compliance shows whether the service is reliable, while incident metrics show whether the team is detecting and handling problems efficiently. Track both together.

These metrics should support investigation, not become isolated scorecards. A service can meet its availability SLO while its MTTA quietly increases, a signal of weakening alert routing or on-call coverage. John Lewis & Partners saw this kind of routing fix pay off directly: after tightening alert routing with PagerDuty, MTTA dropped from 10–15 minutes to 1–2 minutes, restoring service roughly 3x faster. “PagerDuty has improved our incident acknowledgement times from 10-15 minutes to just 1-2 minutes,” says Jacek Materna, DevOps Architect at John Lewis & Partners.

Why do SLAs, SLOs, and SLIs matter?

Together, SLAs, SLOs, and SLIs connect customer expectations, engineering targets, and measured service performance into one operating model. A strong reliability program uses all five parts below.

1. SLAs define what the company promises.
2. SLOs set the reliability level teams manage day to day.
3. SLIs measure actual performance against that level.
4. Error budgets guide trade-offs between reliability and change.
5. Incident workflows detect, escalate, mitigate, and learn from SLO risk.

This structure keeps incident response focused on user impact and measurable reliability outcomes, rather than reacting to every metric fluctuation.

Put SLO tracking to work in your incident response

Defining SLAs, SLOs, and SLIs is only half the job. The other half is making sure a breach reaches the right responder, with the context to act on it fast. When your SLO tooling detects a breach or a fast-burning error budget, PagerDuty takes that alert and handles the rest, from routing and triage to automated remediation, so teams spend less time reconstructing context and more time resolving what matters. Start a free trial today.

Frequently asked questions

What should teams do when an SLO is breached?

Confirm the SLI measurement, assess customer impact, check the burn rate, and follow the relevant severity and escalation policy. Responders should document the breach and review it after recovery.

How can teams reduce monitoring noise while protecting SLOs?

Page only on actionable user impact or rapid error-budget consumption. Diagnostic metrics can remain available for investigation without triggering an incident for every brief fluctuation.

How can automation reduce the impact of an SLO breach?

Automation can enrich alerts with service ownership and SLO context, notify the correct responders, group related signals, run approved diagnostics, and execute safe remediation. Each automated action should have clear limits and an audit trail.

Which SLOs are useful for incident management?

Availability, latency, error rate, and incident-response SLOs are the most common choices. The best selection depends on the service’s critical user journeys and the decisions responders need to make during an incident.

How often should teams review their SLOs?

Review SLOs after significant incidents, major architecture or product changes, and repeated false alerts. Regular reviews help ensure targets still represent customer expectations and operational reality.