What is SLA?
A service level agreement is the contract text that states measurable service targets and what the provider owes when it misses them. It names the indicator, the target value, the measurement window and the remedy, normally service credits. A percentage published without a measurement method or a credit schedule is a marketing claim rather than a commitment.
A usable agreement names four things: the indicator being measured, the target value, the window it is averaged over, and the remedy for a miss. Engineering teams separate the indicator (SLI), the internal target (SLO) and the external promise (SLA), and the contractual number is deliberately looser than the internal goal so a provider can miss its own target without owing anything. Support terms usually live in the same document, expressed as a first-response time per severity level. A response-time target is not a resolution guarantee, and vendors rarely promise the latter.
Remedies are almost always service credits, calculated as a share of the monthly fee for the affected service and capped at that fee. They compensate for what you paid, never for the revenue you lost while the service was down. Credits are also claim-based in most contracts: you have to notice the breach and file inside a stated window, citing the provider's monitoring data. No vendor sends a refund on its own initiative, and an unclaimed credit expires quietly at the end of the period.
Read the exclusions before the headline number. Standard carve-outs cover announced maintenance, force majeure, networks the provider does not operate, and anything caused by your own configuration. Proxy services carry one more that catches people out, because no agreement guarantees that a destination website will serve you. Blocks, CAPTCHAs and rate limiting belong to the target, so they sit outside availability terms even when they stop the work completely. That gap is why success rate and uptime need separate tracking.
On consumption-priced services with no monthly commitment, credits have little to bite on, and the working remedy is that you stop spending. Withholding volume moves a vendor faster than a credit claim does. A formal agreement earns its place at contract scale, where a termination right for repeated breach and an agreed measurement source are worth more than any headline percentage. Ask who owns the authoritative monitoring, and ask what the vendor does after a third consecutive bad month rather than after the first.
Where you meet it
You meet an SLA twice: during vendor selection, and during the argument that follows an outage. The questions that pay off are unglamorous ones about which monitoring system counts and how a credit gets claimed. Ask what period the percentage is averaged over too. If a provider's site lists a number with no measurement method and no remedy attached, file it as an internal target the vendor aims at rather than something you can enforce.
Common questions
What is the difference between an SLA, an SLO and an SLI?
The SLI is the raw measurement, such as the fraction of successful probes. The SLO is the internal target the team runs against. The SLA is the external contractual promise with a remedy attached, and it is normally set below the internal target so the provider has headroom before owing credits.
Do proxy providers guarantee success rates in an SLA?
Rarely. Availability of the proxy gateway is inside a vendor's control, but whether a destination serves your request is not, so blocks and CAPTCHAs are excluded. Some enterprise contracts include a success-rate target scoped to named domains with a jointly agreed test harness, and that is priced accordingly.
What happens if a provider breaches its SLA?
You file a claim inside the window the contract states, citing the outage period, and receive service credits capped at the monthly fee for the affected service. Consequential losses are excluded almost everywhere. Repeated breach may trigger a termination right, but only if the contract spells one out.
Related terms
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