Free NFA Diagram Maker — Draw NFAs

See it work

NFA diagram examples.

Same tool, four requests. Every drawing below is a real render.

What you type

Draw an NFA over a and b that accepts exactly the strings ending in ab: q0 loops on a and b, q0 can move to q1 on a, and q1 moves to accepting q2 on b.

Then tryAdd a dead state for a completed input that is rejected.Change the target suffix from ab to ba.

State diagram · OMG UML 2.5.1 §14 + Harel (1987) statechart · schematex-state

Rather start from a finished drawing? Browse 40 state diagram templates →

The drawing

What an NFA diagram is.

An NFA diagram is a state diagram for a nondeterministic finite automaton. Circles are states, arrows are transitions, an incoming arrow marks the start, and a double circle marks an accepting state.

Unlike a DFA, an NFA may take more than one transition on the same input symbol and may use epsilon transitions that consume no input. A string is accepted when at least one possible path finishes in an accepting state.

Standard: OMG UML 2.5.1 §14 + Harel (1987) statechart
Engine: schematex-state
Editable: Double-click text, drag nodes
Export: SVG · PNG · PDF

Who uses it

Who uses NFA diagrams.

Computer science students

Regular-language exercises that show how a machine recognizes a suffix, prefix or substring.

Theory instructors

Small epsilon-NFA constructions that make a regular-expression union visible in class notes.

Language and parser designers

Alternative token prefixes drawn as branches before they are converted into an implementation.

How it works

How to make an NFA diagram in three steps.

Describe it

One paragraph is enough to start.

“Draw an NFA over a and b that accepts exactly the strings ending in ab: q0 loops on a and b, q0 can move to q1 on a, and q1 moves to accepting q2 on b.”

See the drawing

Drawn by the right engine.

Say what changes

Every edit keeps a version.

Add a dead state for a completed input that is rejected.

V2 · DRAWN FROM V1, NOTHING RETYPED

FAQ

Common questions

What is an NFA?

A nondeterministic finite automaton is a finite-state machine that may have several possible transitions for one input symbol. It accepts when at least one path through the machine ends in an accepting state.

How is an NFA different from a DFA?

A DFA has one next state for each state and input symbol. An NFA can branch to several states and can include epsilon transitions, but NFAs and DFAs recognize the same class of regular languages.

What is an epsilon transition?

An epsilon transition changes state without consuming a character from the input. It is commonly used to join or split branches when building an NFA from a regular expression.

How are accepting states shown?

An accepting, or final, state is shown with a double circle. The machine accepts only if some path ends in that state after all input is read.

Can I make an NFA from a regular expression?

Yes. Describe the expression and its alphabet, then name any grouping or alternation you want to make explicit in the state diagram.

Related tools