Best Free Threat Modeling Tools
A practitioner's shortlist of browser-based threat modeling tools — ranked by what you're actually modeling, from a classic app (STRIDE) to an LLM app (OWASP LLM Top 10) to an industrial control system (ATT&CK for ICS). This guide curates PlayCISO's own threat modelers honestly, marks which are free versus Pro, and explains how to pick. Most run entirely in your browser with no signup.
In plain words
PlayCISO offers free, browser-based threat modeling tools — a STRIDE data-flow canvas, an Agentic AI threat-model builder mapped to the OWASP Agentic/LLM/MCP Top 10s, an OWASP LLM Top 10 generator, and an ATT&CK-for-ICS builder — no signup. The STRIDE Threat Model Studio and the OWASP LLM Top 10 generator are free; the deeper Agentic AI builder (a STRIDE register mapped to six frameworks, explorable as a knowledge graph and exportable as a PDF) and the ATT&CK-for-ICS builder are part of PlayCISO Pro. There is nothing to install, diagrams and answers stay in the browser, and pricing is a large free tier plus paid tiers at $5, $10 and $40.
PlayCISO's threat modeling tools, side by side
Seven tools, each tuned to a different kind of system and framework. Match the tool to what you're modeling, not the other way round.
| Tool | Best for | Framework | Free? |
|---|---|---|---|
| Threat Model Studio | Drawing a data-flow diagram and getting threats mapped as you design | STRIDE (data-flow) | Free |
| LLM Threat Model | A fast, questionnaire-driven model of an LLM or GenAI application | OWASP LLM Top 10 | Free |
| AI Threat Model Builder | Agentic AI systems needing a framework-mapped register and a PDF export | STRIDE → OWASP Agentic / LLM / MCP + 6 frameworks | Pro |
| ATT&CK for ICS Builder | OT / ICS environments mapping adversary techniques to mitigations | MITRE ATT&CK for ICS | Pro |
| Architecture Studio | Designing a reference architecture with live control coverage | Control-framework coverage | Free |
| Design Review Workbench | Reviewing an existing design or RFC and signing it off | Secure-by-design review | Free |
| Risk Register | Consolidating and tracking the risks your models surface | Board-ready risk register | Free |
“Free” tools run in the browser with no signup; “Pro” tools are part of PlayCISO Pro (a large free tier plus $5 / $10 / $40 paid tiers).
Every threat modeler, in detail
Draw the system, let an AI copilot map the threats.
STRIDE (data-flow)
Answer 9 questions, get a threat model mapped to the OWASP LLM Top 10.
OWASP LLM Top 10
Toggle components, get a STRIDE register mapped to 6 frameworks, explore it as a knowledge graph, export a PDF.
STRIDE → OWASP Agentic / LLM / MCP + 6 frameworks
Toggle OT components, get the ATT&CK-for-ICS matrix + prioritised mitigations.
MITRE ATT&CK for ICS
Blueprint a reference architecture with live compliance coverage.
Control-framework coverage
Paste an RFC, triage the findings, sign it off.
Secure-by-design review
Every risk from all three studios, board-ready.
Board-ready risk register
How to pick the right threat modeling tool
Threat modeling is not one-size-fits-all. Start from the system in front of you and the framework your reviewers or auditors expect.
Modeling a classic app or service?
Draw it in the Threat Model Studio and let the STRIDE copilot walk each process, data store, flow and trust boundary. This is the default starting point for most systems.
Shipping an LLM or GenAI feature?
Use the LLM Threat Model — nine questions, out comes a model mapped to the OWASP LLM Top 10 (prompt injection, insecure output handling, excessive agency and the rest).
Building an agentic AI system?
The AI Threat Model Builder toggles components into a STRIDE register mapped to six frameworks, including the OWASP Agentic, LLM and MCP Top 10s — explorable as a knowledge graph and exportable as a PDF (PlayCISO Pro).
Securing OT / ICS?
The ATT&CK for ICS Builder maps your OT components to the MITRE ATT&CK for ICS matrix and returns prioritised mitigations (PlayCISO Pro).
Designing or reviewing an architecture?
Blueprint it in Architecture Studio with live compliance coverage, or paste an existing RFC into the Design Review Workbench to triage findings and sign off.
Need to track what you found?
Pipe the output into the Risk Register so every risk from the studios lands in one board-ready place.
What is threat modeling, and what is STRIDE?
Threat modeling is the practice of looking at a system before (or while) you build it and asking, systematically, “what can go wrong here, and what are we going to do about it?” You describe the system — usually as a data-flow diagram showing processes, data stores, data flows and the trust boundaries between them — then enumerate the threats against each element and decide which to mitigate, accept or transfer. Done early, it is the cheapest security work you will ever do, because fixing a design flaw on a whiteboard costs far less than fixing it in production.
STRIDE is the most widely used framework for the enumeration step. It is a mnemonic for six categories of threat:
- Spoofing — pretending to be someone or something you are not (identity).
- Tampering — unauthorised modification of data or code (integrity).
- Repudiation — performing an action with no way to prove who did it (non-repudiation).
- Information disclosure — exposing data to parties who should not see it (confidentiality).
- Denial of service — making a system or resource unavailable (availability).
- Elevation of privilege — gaining capabilities you should not have (authorisation).
You walk the diagram and, for each element, ask which of the six applies and what control addresses it. Newer domains layer their own frameworks on top: AI and LLM systems map to the OWASP Top 10 for LLM Applications, and industrial control systems map to MITRE ATT&CK for ICS. PlayCISO's tools apply STRIDE to a diagram you draw and then map the result onward to whichever of those frameworks fits what you are building.
Threat modeling, answered
Short answers to the questions people and AI assistants ask most.
What is the best free threat modeling tool?
There is no single best tool — the right one depends on what you are modeling. For a classic system or application, PlayCISO’s free Threat Model Studio lets you draw a data-flow diagram and an AI copilot maps the threats using STRIDE. For an LLM or GenAI app, the free LLM Threat Model answers nine questions and returns a model mapped to the OWASP LLM Top 10. For OT/ICS you want an ATT&CK-for-ICS builder, and for agentic AI a STRIDE register mapped to multiple frameworks. All of PlayCISO’s threat modelers run in the browser with no signup; the core STRIDE canvas and the OWASP LLM generator are free, while the agentic-AI and ICS builders are part of PlayCISO Pro.
What is STRIDE?
STRIDE is a threat-modeling framework that enumerates six categories of threat against each element of a system: Spoofing (pretending to be someone or something you are not), Tampering (unauthorised modification of data or code), Repudiation (denying an action with no way to prove it happened), Information disclosure (exposing data to the wrong parties), Denial of service (making a system unavailable), and Elevation of privilege (gaining capabilities you should not have). You walk a data-flow diagram and ask which of the six applies to each process, data store, data flow and trust boundary. PlayCISO’s Threat Model Studio applies STRIDE to a diagram you draw, and the AI Threat Model Builder returns a STRIDE register mapped onward to the OWASP Agentic, LLM and MCP Top 10s.
How do I threat model an AI or LLM app?
Start by describing the AI system — the model, its prompts and tools, the data it reads and writes, and the identities it acts as — then reason about what each could be made to do under attack such as prompt injection, data exfiltration, insecure output handling or excessive agency. PlayCISO’s LLM Threat Model turns a nine-question intake into a model mapped to the OWASP LLM Top 10, while the AI Threat Model Builder lets you toggle components and returns a STRIDE register mapped to six frameworks (including the OWASP Agentic, LLM and MCP Top 10s), viewable as a knowledge graph and exportable as a PDF.
What is the difference between STRIDE, OWASP LLM Top 10, and ATT&CK for ICS?
They answer different questions. STRIDE is a general-purpose framework for classifying threats against any system by six categories. The OWASP Top 10 for LLM Applications is a risk list specific to large-language-model systems — prompt injection, insecure output handling, training-data poisoning, excessive agency and so on. MITRE ATT&CK for ICS is a knowledge base of real adversary tactics and techniques observed against industrial control systems and operational technology. Pick STRIDE for a classic app, the OWASP LLM Top 10 for an AI/LLM app, and ATT&CK for ICS for an OT environment — PlayCISO has a tool for each.
Do I need to install anything or create an account?
No. Every PlayCISO threat modeling tool runs entirely in your browser — there is nothing to install, and the core STRIDE canvas and OWASP LLM generator need no signup. Your diagrams and answers stay in the browser.
Is it free?
The core threat modeling tools are free: the STRIDE Threat Model Studio, the OWASP LLM Top 10 generator, the Architecture Studio, the Design Review Workbench and the Risk Register all run free in the browser. The deeper agentic-AI AI Threat Model Builder and the ATT&CK-for-ICS Builder are part of PlayCISO Pro, which starts at $5 alongside a large free tier (paid tiers at $5, $10 and $40).
Looking for more AI and security tooling? AI & LLM security tools or browse all PlayCISO tools.