SLA glossary
The vocabulary of SLA credits and vendor reliability, in plain English. Start with what is an SLA credit, then look up any term below.
What is an SLA credit?
An SLA credit is the compensation a vendor owes when it misses the uptime commitment in its Service Level Agreement — usually a percentage of the affected month’s fee, claimed with evidence before a deadline. See which vendors pay and estimate yours with a credit calculator.
SLA (Service Level Agreement)
A contractual commitment from a vendor about the level of service it will provide — most importantly a minimum uptime percentage over a measurement period, and the remedy owed if it falls short.
SLA credit
The compensation a vendor owes when it breaches its SLA — usually a percentage of the affected month's fee for the affected service. It is almost never automatic: you must claim it with evidence before a deadline.
What is an SLA credit? →Service credit
The form an SLA credit usually takes: a credit applied against a future invoice rather than a cash refund. In most contracts it is the sole and exclusive remedy for downtime.
SLA credit vs service credit →Uptime (availability)
The percentage of a measurement period during which a service was available. A 99.9% monthly uptime commitment allows roughly 43 minutes of downtime per month; 99.99% allows about 4 minutes.
Downtime
The time a service was unavailable or degraded below its committed level. SLAs define precisely what counts as downtime and what is excluded (see excluded downtime).
The nines
Shorthand for uptime targets by the number of nines: 'three nines' is 99.9%, 'four nines' is 99.99%, 'five nines' is 99.999%. Each extra nine cuts the allowed monthly downtime by about 10x.
SLO (Service Level Objective)
An internal reliability target a team sets for itself (e.g. 99.95% availability). Unlike an SLA it usually carries no contractual credit — it's the goal that keeps the service comfortably inside its SLA.
SLI (Service Level Indicator)
The actual measured metric an SLO or SLA is judged against — for example the ratio of successful requests to total requests, or measured availability over the month.
Error budget
The amount of unreliability an SLO permits — the gap between 100% and the target. A 99.9% objective allows a 0.1% error budget; when it's exhausted, teams typically freeze risky changes.
MTTR (Mean Time To Recovery)
The average time a vendor takes to resolve incidents. Lower MTTR means outages are shorter; it's one of the inputs to Ontracko's reliability score.
See reliability rankings →Claim window
The deadline for filing an SLA credit claim, running from the incident. It is commonly 30 days, though some cloud providers allow 60. Miss it and the credit is forfeited.
Credit tier
A band in an SLA's credit schedule mapping a range of measured uptime to a credit percentage — for example 10% of spend just below target, rising to 25%, 50% or 100% for progressively worse outages.
Measurement period
The window over which uptime is calculated for the SLA — usually a calendar month, sometimes a quarter. It determines how a given outage translates into a percentage and therefore a credit.
Excluded downtime
Periods an SLA does not count against uptime — typically scheduled maintenance, customer-caused issues, force majeure, and beta or free-tier services. Excluded time does not earn a credit.
Incident severity
How impactful an outage is — commonly critical, major, or minor. Severity affects both how downtime is weighted in a reliability score and, for some vendors, which credit applies.
Reliability score
Ontracko's deterministic 0–100 score derived from a vendor's own public status feed over 60 days, penalizing weighted downtime, critical outages, slow recovery and incident frequency — the same data for every vendor.
How scoring works →Status page
The public feed a vendor uses to report incidents and maintenance. It's the primary evidence for an SLA credit claim — the incident reference and timestamps corroborate that an outage occurred.
Frequently asked
What is an SLA credit?
An SLA credit is a partial refund — usually a percentage of the affected month's fee — that a vendor owes when it misses the uptime commitment in its Service Level Agreement. In most cases you must claim it with evidence before a deadline.
What's the difference between an SLA and an SLO?
An SLA is a contractual commitment to a customer, usually with a credit remedy if breached. An SLO is an internal target a team sets for itself, typically with no contractual consequence — it's the goal that keeps the service inside its SLA.
How much downtime does 99.9% uptime allow?
About 43 minutes per month. 99.95% allows roughly 21 minutes, and 99.99% ('four nines') allows about 4 minutes per month.
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