# SLO/SLA Calc — Availability & SLO Planner

> Model system availability and evaluate designs with calculations and visualizations. (iPhone/iPad app by Ruben Calzadilla.)

- Source: https://appshunter.io/ios/app/slosla-calc/id6789262199 (this page in markdown: same URL + `.md`)
- Developer: [Ruben Calzadilla](https://appshunter.io/developer/1130032354)
- Category: Productivity, Utilities
- Price: $1.99
- Rating: 5.00/5 from 1 App Store ratings · 1 written reviews indexed
- Age rating: 4+
- Requires: iOS 17.0 · 5 MB
- Released: 2026-07-16
- Data updated: 2026-09-07
- Monetization: paid
- User reviews in markdown: https://appshunter.io/ios/app/slosla-calc/id6789262199/reviews.md

## What is SLO/SLA Calc?

SLO/SLA Calc helps engineers, architects, SREs, and operators move from Device assumptions to resilient System decisions before deployment.

Model operational availability and time-bound Mission Reliability. Calculate Series, Parallel, N:M, and Cross-Connected topologies. Estimate Device Availability from manufacturer MTBF or documented generic estimates, then account for repair time, spare logistics, support agreements, EOL sourcing, and redundant power. Review exactly how each assumption affects the result.

Save Devices and subsystems as reusable Blocks, then arrange them into larger Systems. With Live Modeling, apply temporary failures to Blocks, internal Components, and switches. Remaining Availability updates immediately while animated Red and Blue paths show which inputs survive. Shared paths become Purple, and optional output switches select a healthy single handoff.

MODEL AVAILABILITY

- Calculate System and Device Availability
- Review a transparent Device calculation breakdown
- Edit the defaults used for new Device calculations
- Translate availability into downtime per day, week, month, or year
- Model Series, Parallel, heterogeneous N:M, and Cross-Connected designs
- Reuse saved Devices as named topology Components

EVALUATE A MISSION

- Estimate Mission Reliability for a defined duration in hours, days, or weeks
- Use stored MTBF or an explicit availability-only assumption
- Compare Mission Success, Interruption Risk, and any-Component failure probability
- See expected failed Components and the weakest individual contributor
- Distinguish provided, estimated, assumption-based, and mixed data

BUILD AND TEST SYSTEMS

- Assemble Systems from reusable Blocks and ordered Stages
- Use Direct or Full Cross multi-path Handoffs
- Add optional output switches and explicit Ideal Paths
- Simulate Block, Component, and switch failures
- Trace surviving flows in portrait or full-screen landscape

COMPARE AND SHARE

- Compare complete Systems and quantify downtime reduction
- Evaluate a design against a target SLO
- See remaining or exceeded error budget
- Generate and share professional PDF reports
- Export, share, preview, and import editable JSON-based .slosla files
- Edit imported Block Components and recalculate the design

Learn through an expanded Guided Tour, worked examples, formulas, model assumptions, and practical design guidance.

SLO/SLA Calc works entirely offline and stores Device defaults, Blocks, and Systems locally on your device. No account is required. Files leave your device only when you choose to export or share them.

One purchase unlocks the complete app. No ads, analytics, tracking, subscriptions, or in-app purchases.

## Key features

- Calculate system and device availability
- Model series, parallel, and N:M designs
- Estimate device availability using MTBF, MTTR
- Save and reuse devices/subsystems as Blocks
- Build larger Systems by connecting Blocks
- Visualize system architecture
- Generate and share PDF reports

## Chart rankings

- #199 in Top Paid · Productivity (US App Store)

## Recent user reviews (1 of 1)

All indexed reviews: https://appshunter.io/ios/app/slosla-calc/id6789262199/reviews.md

### 5/5 — Finally a great SLO/SLA tool

*2026-07-18*

I’m so impressed with this SLO and SLA calculator, the author expends a lot of time covering all needed to design high availability systems, also to calculate promises of vendors understanding what you are getting before, the reference explain in detail how to use the calculator, this is amazing tool! Highly recommended.

## Frequently asked questions about SLO/SLA Calc

### What is SLO/SLA Calc used for?

SLO/SLA Calc is used by engineers and operators to model system availability and evaluate designs before deployment. It helps calculate availability for various configurations and estimate device reliability.

### How does SLO/SLA Calc calculate availability?

It calculates availability for series, parallel, and N:M designs. It can also estimate device availability using metrics like MTBF, MTTR, spare availability, and EOL status.

### Can I reuse components in SLO/SLA Calc?

Yes, you can save devices and subsystems as reusable Blocks. These Blocks can then be combined into larger Systems, allowing for efficient modeling of complex architectures.

### Does SLO/SLA Calc work offline?

Yes, SLO/SLA Calc works offline. Saved Blocks and Systems are stored locally on your device, and no account is required to use the app.

### What kind of reports can SLO/SLA Calc generate?

SLO/SLA Calc can generate and share professional PDF system reports. These reports help visualize the resulting architecture and compare performance against a target SLO.

### What is the price of SLO/SLA Calc?

SLO/SLA Calc is a paid application priced at $1.99.

### How often is SLO/SLA Calc updated?

The latest version, 1.2, was released on July 19, 2026, indicating recent development activity. The app was initially released on July 16, 2026.

### Does SLO/SLA Calc have ads?

No, SLO/SLA Calc does not contain advertisements. It is a paid application that offers an ad-free experience.

## Version history (last 5 releases)

### 1.5 — 2026-08-27

Version 1.5 connects individual Device assumptions to complete mission decisions.

TRANSPARENT DEVICE AVAILABILITY

- Review a complete calculation breakdown: base MTBF, redundant-power benefit, spare logistics, EOL delay, eligible support benefit, hands-on repair time, and modeled restoration time.
- Edit app-wide defaults for generic Device MTBF, redundant power, logistics, EOL sourcing, and support-agreement behavior.
- See exactly when support changes the result. Support reduces eligible logistics and EOL delay only; it never reduces hands-on repair time.
- Preserve the assumptions and MTBF provenance used by every saved Device, even when app-wide defaults later change.

REUSE REAL DEVICE DATA

- Select saved Devices directly as named Components in Series, Parallel, N:M, and Cross-Connected topologies.
- Preserve Device names, availability, MTBF, and provenance through Blocks, Systems, exports, imports, and edits.

NEW MISSION RELIABILITY

- Evaluate whether a saved Device, Block, or System can complete a continuous mission measured in hours, days, or weeks without a service interruption.
- Use stored MTBF when available, or explicitly model availability-only inputs using average restoration time or a reliability reference period.
- Keep strict MTBF validation when assumptions are not appropriate.
- Compare Mission Success, Interruption Risk, any-Component failure probability, expected failed Components, and the weakest contributor.
- Apply existing Series, Parallel, heterogeneous N:M, Cross-Connected, Stage, and Handoff logic to mission survival.
- See clear provided, estimated, assumption-based, and mixed data-quality labels.

BETTER GUIDANCE

- Follow an expanded Guided Tour from Device calculation and reuse through complex System construction, Live Modeling, SLO Analysis, System Comparison, and Mission Reliability.
- Review new formulas, assumptions, limitations, worked examples, and Reliability Block Diagram guidance in Reference.
- Benefit from additional layout, naming, and consistency improvements across iPhone and iPad.

Mission Reliability uses a constant-rate, independent-failure model with no repair during the mission. Availability-only methods require an explicit assumption and are clearly labeled as approximate.

### 1.4 — 2026-08-10

Version 1.4 turns saved Systems into interactive resilience models you can test, inspect, and share.

LIVE MODELING
- Apply temporary failures without changing the saved System.
- Fail an entire Block, an internal Component, or a modeled output switch.
- See Remaining Availability and service status recalculate immediately.
- Restore individual elements or reset the complete simulation.

VISIBLE INPUT FLOWS
- Follow animated Red and Blue dashed paths through the surviving topology.
- See shared connections become Purple when both inputs use the same route.
- Distinguish enabled, delivered, and interrupted inputs.
- Observe a single-output switch select one healthy handoff.

FULL-SCREEN SIMULATION
- Expand Live Modeling into a dedicated interactive canvas.
- Rotate iPhone or iPad for a wider landscape view of longer Systems.
- Keep topology, flow behavior, availability, and failure state visible together.

EDITABLE SYSTEM SHARING
- Export and share complete Systems as portable .slosla files.
- Use the documented JSON-based data model to preserve Blocks, Components, stages, handoffs, switches, and calculated values.
- Send designs through Files, AirDrop, Mail, Messages, or other compatible apps.
- Preview, validate, recalculate, and safely import a shared System without overwriting local work.
- Edit imported Block Components and update their availability values.
- Continue modeling, comparing, reporting, and simulating the imported design.

MORE MODELING CONTROL
- Add an explicit 100% Ideal Path to represent an intentional passive bypass. Ideal Paths are non-failable during simulation.
- Use topology-aware failure behavior for Series, Parallel, N:M, and Cross-Connected Blocks.
- Compare extremely close designs with additional precision when fixed decimal places would hide the difference.
- Share either a professional PDF report or the complete editable System model.

LEARNING AND POLISH
- Expanded Guided Tour covering Live Modeling and editable System sharing.
- Updated How to Use and Reference material for the new workflow and terminology.
- Refined failure labels, flow legends, output-switch behavior, and full-screen layouts.
- Refreshed app icon.

SLO/SLA Calc still works entirely offline. Simulations never modify a saved System, and files leave your device only when you choose to export or share them.

### 1.3 — 2026-08-01

Version 1.3 makes advanced availability modeling easier to build, understand, and explain.

CROSS-CONNECTED TOPOLOGIES
- Model two-layer and three-layer Cross-Connected Blocks.
- Assign a different availability value to every component.
- Connect compatible multi-path stages using Direct or Full Cross handoffs.
- Add an optional output switch when multiple paths converge into one handoff.

SYSTEM COMPARISON
- Compare two saved Systems side by side.
- See availability differences, calculated downtime reduction, and design complexity.
- Optionally evaluate both Systems against the same target SLO.
- Get a clear decision summary explaining which design provides greater modeled availability.

IMPROVED GUIDANCE
- Follow an expanded guided tour with a worked Parallel example.
- Load the example directly into the calculator and explore the result.
- Review consistent definitions for Components, Blocks, Layers, Paths, Stages, Handoffs, and Systems.
- Learn about common availability design pitfalls involving infrastructure, shared failure domains, cloud regions, security, manual intervention, and recovery testing.

REPORTING AND RELIABILITY
- View Cross-Connected architecture and handoffs in System diagrams and PDF reports.
- Improved editing and deletion behavior for complex System stages.
- Additional usability and stability improvements throughout the app.

### 1.2 — 2026-07-19

Version 1.2 turns SLO/SLA Calc into a more complete availability design workspace.
• Organize saved calculations into reusable Blocks and complete Systems
• Build larger systems by connecting Blocks in series or parallel
• Add optional output-switch availability to parallel stages
• Edit saved Blocks and Systems as designs evolve
• Automatically identify Systems that require recalculation after a Block changes
• Visualize the complete system topology with availability values
• Generate and share a professional PDF system report
• Improved guidance, terminology, empty states, and reference documentation
• Additional usability, stability, and interface improvements for iPhone and iPad

### 1.1 — 2026-07-16

No release notes.

## Related topics

[dillas](https://appshunter.io/ios/topics/dillas)

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*Data collected daily from the US App Store and indexed by [AppsHunter](https://appshunter.io/). User reviews are verbatim App Store reviews. Ratings, prices and chart positions refresh continuously; this snapshot is from 2026-09-07.*