diff --git a/src/Dagger.jl b/src/Dagger.jl
index 0c3761c4..584d8b8f 100644
--- a/src/Dagger.jl
+++ b/src/Dagger.jl
@@ -67,6 +67,7 @@ include("thunk.jl")
 include("submission.jl")
 include("chunks.jl")
 include("memory-spaces.jl")
+include("rules.jl")
 
 # Task scheduling
 include("compute.jl")
diff --git a/src/rules.jl b/src/rules.jl
new file mode 100644
index 00000000..0d67f0ec
--- /dev/null
+++ b/src/rules.jl
@@ -0,0 +1,76 @@
+struct Rule
+    action::Function
+    inputs::Vector{String}
+    outputs::Vector{String}
+    forcerun::Bool
+
+    function Rule(action::Function, inputs::Vector{String}, outputs::Vector{String}, forcerun::Bool)
+        new(action, inputs, outputs, forcerun)
+    end
+end
+
+# String inputs/outputs variants
+Rule(action::Function, inputs::String, outputs::String; forcerun::Bool=false) = 
+    Rule(action, [inputs], [outputs], forcerun)
+
+Rule(action::Function, inputs::Vector{String}, outputs::String; forcerun::Bool=false) = 
+    Rule(action, inputs, [outputs], forcerun)
+
+Rule(action::Function, inputs::String, outputs::Vector{String}; forcerun::Bool=false) = 
+    Rule(action, [inputs], outputs, forcerun)
+
+Rule(action::Function, io::Pair; forcerun::Bool=false) = 
+    Rule(action, io.first, io.second; forcerun)
+
+Rule(action::Function, inputs::Vector{String}, outputs::Vector{String}; forcerun::Bool=false) = 
+    Rule(action, inputs, outputs, forcerun)
+
+function Base.show(io::IO, r::Rule)
+    print(io, "Rule(")
+    print(io, r.action)
+    
+    # Show inputs and outputs
+    in_str = length(r.inputs) == 1 ? "\"$(r.inputs[1])\"" : string(r.inputs)
+    out_str = length(r.outputs) == 1 ? "\"$(r.outputs[1])\"" : string(r.outputs)
+    print(io, ", ", in_str, " => ", out_str)
+    
+    # Show forcerun if true
+    r.forcerun && print(io, "; forcerun=true")
+    
+    print(io, ")")
+end
+
+function Base.show(io::IO, ::MIME"text/plain", r::Rule)
+    println(io, "Rule(;forcerun=$(r.forcerun)):")
+    println(io, "  Action:      ", r.action)
+    println(io, "  Inputs:      ", r.inputs)
+    println(io, "  Outputs:     ", r.outputs)
+end
+
+function needs_update(task::Rule)
+    
+    # all input files should be present so I can check their dates
+    missingfiles = @. !isfile(task.inputs)
+    any(missingfiles) && throw(AssertionError("Rule declares $(task.inputs) as input\n but $(task.inputs[missingfiles]) do not exist."))
+
+    task.forcerun && return true
+    any(!isfile, task.outputs) && return true
+
+    # Get the latest modification time of inputs
+    input_mtime = maximum(mtime.(task.inputs))
+    # Get the earliest modification time of outputs
+    output_mtime = minimum(mtime.(task.outputs))
+    # Run if any input is newer than any output
+    input_mtime > output_mtime
+end
+
+function (task::Rule)(inputs...) # Inputs in not used, only for dagger to build the DAG
+
+    if needs_update(task)
+        "[RUN] Running $(task) (thread $(Threads.threadid()))" |> println
+        task.action(task.inputs, task.outputs)
+    else
+        "[ - ] Skipping $(task)" |> println
+    end
+    task.outputs
+end
\ No newline at end of file
diff --git a/test/rules.jl b/test/rules.jl
new file mode 100644
index 00000000..611995ac
--- /dev/null
+++ b/test/rules.jl
@@ -0,0 +1,122 @@
+
+@testset "Rules" begin
+
+# test basic patterns
+mktempdir() do dir
+
+    write("$(dir)/a.txt", "a")
+    write("$(dir)/b.txt", "b")
+
+    rule_write(x, y) = Dagger.Rule(x => y; forcerun=true) do input, output
+        write(output[1], read(input[1], String))
+        output
+    end
+
+    rule_merge(x, y) = Dagger.Rule(x => y; forcerun=true) do input, output
+        write(output[1], join(read.(input, String)))
+        output
+    end
+
+    # Linear: a -> b -> c
+    r1 = rule_write("$(dir)/a.txt", "$(dir)/b1.txt")
+    r2 = rule_write("$(dir)/b1.txt", "$(dir)/c.txt")
+    t1 = Dagger.@spawn r1()
+    t2 = Dagger.@spawn r2(t1)
+    @test read(fetch(t2)[1], String) == "a"
+
+    # Fan-in: a.txt, b.txt -> ab.txt
+    r3 = rule_merge(["$(dir)/a.txt", "$(dir)/b.txt"], "$(dir)/ab.txt")
+    t3 = Dagger.@spawn r3()
+    @test read(fetch(t3)[1], String) == "ab"
+
+    # Fan-out: a.txt -> a1.txt, a2.txt
+    r4 = Dagger.Rule("$(dir)/a.txt" => ["$(dir)/a1.txt", "$(dir)/a2.txt"]; forcerun=true) do i, o
+        for f in o; 
+            write(f, read(i[1], String))
+        end
+        o
+    end
+    t4 = Dagger.@spawn r4()
+    @test read.(fetch(t4), String) == ["a", "a"]
+
+    # Diamond: a -> b,c -> d
+    r5 = rule_write("$(dir)/a.txt", "$(dir)/b.txt")
+    r6 = rule_write("$(dir)/a.txt", "$(dir)/c.txt")
+    r7 = rule_merge(["$(dir)/b.txt", "$(dir)/c.txt"], "$(dir)/d.txt")
+    tb = Dagger.@spawn r5()
+    tc = Dagger.@spawn r6()
+    td = Dagger.@spawn r7(tb, tc)
+    @test read(fetch(td)[1], String) == "aa"
+end
+
+# more realistic use case
+mktempdir() do dir
+
+    # avoid CSV & DataFrame dependency in tests
+    writefile(file, x) = begin
+        open(file, "w") do io
+            for i in 1:length(x)-1
+                write(io, string(x[i]) * "\n")
+            end
+            write(io, string(x[end]))
+        end
+    end
+
+    readfile(file) = read(file, String) |> x->split(x, "\n") .|> x->parse(Float64, x)
+    
+    x = rand(10)
+    writefile("$(dir)/test.txt", x)
+    @test x == readfile("$(dir)/test.txt")
+
+    # prepare inputs
+
+    sum_squared_input = Float64[]
+    for sample_idx in 1:5
+        x = rand(10)
+        writefile("$(dir)/sample_$(sample_idx).csv", x)
+        push!(sum_squared_input, sum(x.^2))
+    end
+
+    samples = ["$(dir)/sample_$(sample_idx).csv" for sample_idx in 1:5]
+
+    # define and run
+
+    get_rule_square(sample) = Dagger.Rule(sample => replace(sample, "sample_" => "sample_squared_"); forcerun=false) do input, output
+        x = readfile(input[1])
+        xsquared = x .^ 2
+        writefile(output[1], xsquared)
+        output
+    end
+
+    squared_rules = get_rule_square.(samples)
+    squared_rule_outputs = [only(r.outputs) for r in squared_rules]
+
+    make_summary = Dagger.Rule(squared_rule_outputs => "$(dir)/samples_summary.csv"; forcerun=false) do inputs, output
+        xs = readfile.(inputs)
+        sum_squared = [sum(x) for x in xs]
+        writefile(output[1], sum_squared)
+        output
+    end
+
+    squared = [Dagger.@spawn r() for r in squared_rules]
+    @warn "running first summary_file"
+    summary_file = Dagger.@spawn make_summary(squared...)
+    
+    out = readfile(fetch(summary_file)[1])
+    
+    @test out == sum_squared_input
+
+    @test Dagger.needs_update(make_summary) == false
+    sleep(1)
+    run(`touch $(squared_rule_outputs[1])`)
+    sleep(1)
+    @test Dagger.needs_update(make_summary) == true
+
+    run(`rm $(squared_rule_outputs[1])`)
+    @warn "running second summary_file"
+    summary_file = Dagger.@spawn make_summary(squared...)
+    @test_throws Dagger.DTaskFailedException fetch(summary_file)
+
+end
+
+end
\ No newline at end of file
diff --git a/test/runtests.jl b/test/runtests.jl
index 39860cf2..593bae59 100644
--- a/test/runtests.jl
+++ b/test/runtests.jl
@@ -22,6 +22,7 @@ tests = [
     ("Datadeps", "datadeps.jl"),
     ("Streaming", "streaming.jl"),
     ("Domain Utilities", "domain.jl"),
+    ("Rules", "rules.jl"),
     ("Array - Allocation", "array/allocation.jl"),
     ("Array - Indexing", "array/indexing.jl"),
     ("Array - Core", "array/core.jl"),