Your first effect

From an empty directory to a running NS_Hello — one .dfs, one command, one standard UNiagaraSystem.

Fifteen minutes, no editor required.

Write the source

Create Effects/NS_Hello.dfs under the project's DFX/:

System(Name="Effects/NS_Hello", Root="Game")
{
    Settings = {
        WarmupTime  = 0.0;
        FixedBounds = box(-100, -100, -100, 100, 100, 100);
    }

    // Exposed to blueprint as User.Speed, and settable with SetNiagaraVariableFloat.
    Properties = {
        float Speed = 150.0 [ Group="Motion" ];
    }

    Emitter Motes
    {
        Settings = {
            SimTarget          = CPU;
            Determinism        = true;
            RandomSeed         = 1;
            AllocationMode     = Fixed;
            PreAllocationCount = 64;
        }

        EmitterUpdate = {
            EmitterState(LifeCycleMode = Self, LoopBehavior = Infinite);
            SpawnRate(SpawnRate = 20.0);
        }

        ParticleSpawn = {
            Spawn/Initialization/V2/InitializeParticle(
                LifetimeMode      = DirectSet,
                Lifetime          = 2.0,
                SpriteSizeMode    = Uniform,
                UniformSpriteSize = 8.0
            );
            SystemLocation();
            AddVelocityInCone(ConeAngle = 30.0, VelocityStrength = User.Speed);
        }

        ParticleUpdate = {
            // Advances NormalizedAge. Anything age-driven needs it, and Niagara reports an
            // unmet dependency if it is missing.
            ParticleState();
            GravityForce(Gravity = (0, 0, -400));
            SolveForcesAndVelocity();
        }

        SpriteRenderer Core
        {
            Alignment  = Unaligned;
            FacingMode = FaceCamera;
            SortMode   = ViewDepth;
        }
    }
}

The header's Root="Game" says which content root Name="..." is relative to, so this file builds /Game/Effects/NS_Hello.

Build it

pwsh -File Plugins/DreamFX/.skill/dfx.ps1 build DFX/Effects/NS_Hello.dfs

You should see 1 built, 0 up to date, 0 failed | 0 error(s), and the asset listed under "Assets written to disk by this run". Open /Game/Effects/NS_Hello in the editor and it plays.

A second build with no edits reports 0 built, 1 up to date — the provenance stamp on the asset holds a hash of the source, and a matching hash means there is nothing to do. -Force overrides it.

Change one number and build again

Change SpawnRate from 20.0 to 60.0 and build again. This time it rebuilds — the hash moved.

That is the whole loop: the text is the only authoring surface, and the asset is build output. Do not edit a generated asset in the Niagara editor; the next rebuild wipes the edit, and does not ask first.

When it does not compile

Every diagnostic is a DFXnnnn with a file, line and column:

DFX/Effects/NS_Hello.dfs(31,17): error DFX3003: Module 'GravityForce' has no input named 'Gravty'.
Did you mean 'Gravity'? Available inputs: Gravity, CoordinateSpace

Two things to reach for:

Diagnostics — every code, with what causes it and how to fix it;
dfx.ps1 schema <Module> — a module's real input signature, read from the asset. This is the authority on names: Niagara input names contain spaces (Loop Duration), which DreamFX normalises, and some inputs only exist once a static switch above them is set.

pwsh -File Plugins/DreamFX/.skill/dfx.ps1 schema GravityForce

Leaving ParticleState() out is not a syntax error — it surfaces as Niagara's own unmet dependency. It advances NormalizedAge, which every age-driven module reads.

Things to try next

Swap VelocityStrength for a random range, to see how a nested dynamic input is written:
```
AddVelocityInCone(
    ConeAngle        = 30.0,
    VelocityStrength = RandomRangeFloat(
        Minimum        = User.Speed * 0.5,
        Maximum        = User.Speed,
        RandomnessMode = SimulationDefaults
    )
);
```
RandomnessMode is a static switch. On a module a switch has to be written before the inputs it gates; on a dynamic input that rule is relaxed — switches are hoisted — so the order above works either way round. See values and rules.

Add a colour fade driven by a curve:

ParticleUpdate = {
    ParticleState();
    ScaleColor(
        ScaleAlpha = FloatFromCurve(
            FloatCurve = curve { 0.0 -> 1.0; 1.0 -> 0.0; },
            CurveIndex = Particles.NormalizedAge
        )
    );
}

Layout and naming

DFX/ roots, how Root and Name resolve, module search paths.

The `.dfs` reference

Settings, Properties, the six stacks, renderers, from, Defaults.