diff --git a/.claude/settings.json b/.claude/settings.json
new file mode 100644
index 0000000..0c6a354
--- /dev/null
+++ b/.claude/settings.json
@@ -0,0 +1,23 @@
+{
+  "permissions": {
+    "allow": [
+      "Bash(julia --project=. -e 'using Pkg; Pkg.test\\(\\)')"
+    ]
+  }
+}
+{
+  "hooks": {
+    "PostToolUse": [
+      {
+        "matcher": "Edit|Write",
+        "hooks": [
+          {
+            "type": "command",
+            "command": "python3 -c \"import sys,json; d=json.load(sys.stdin); print(d['tool_input'].get('file_path',''))\" | { read -r f; [[ \"$f\" == *.jl ]] && runic -i \"$f\"; } 2>/dev/null || true",
+            "statusMessage": "Formatting Julia with Runic..."
+          }
+        ]
+      }
+    ]
+  }
+}
diff --git a/.git-blame-ignore-revs b/.git-blame-ignore-revs
new file mode 100644
index 0000000..c32bbdf
--- /dev/null
+++ b/.git-blame-ignore-revs
@@ -0,0 +1,2 @@
+# runic formatting
+fbb2336
diff --git a/.github/workflows/CI.yml b/.github/workflows/CI.yml
index 6ac1e04..7f73548 100644
--- a/.github/workflows/CI.yml
+++ b/.github/workflows/CI.yml
@@ -13,15 +13,15 @@ jobs:
       fail-fast: false
       matrix:
         version:
-          - '1.1'
+          - 'min'
           - '1'
         os:
           - ubuntu-latest
         arch:
           - x64
     steps:
-      - uses: actions/checkout@v2
-      - uses: julia-actions/setup-julia@v1
+      - uses: actions/checkout@v4
+      - uses: julia-actions/setup-julia@v2
         with:
           version: ${{ matrix.version }}
           arch: ${{ matrix.arch }}
@@ -40,6 +40,6 @@ jobs:
       - uses: julia-actions/julia-buildpkg@v1
       - uses: julia-actions/julia-runtest@v1
       - uses: julia-actions/julia-processcoverage@v1
-      - uses: codecov/codecov-action@v1
+      - uses: codecov/codecov-action@v4
         with:
           file: lcov.info
diff --git a/.gitignore b/.gitignore
index 49541d3..a174b0a 100644
--- a/.gitignore
+++ b/.gitignore
@@ -3,3 +3,4 @@
 *.jl.mem
 deps/deps.jl
 Manifest.toml
+Manifest-v*.toml
diff --git a/Project.toml b/Project.toml
index 53143e8..bab9a46 100644
--- a/Project.toml
+++ b/Project.toml
@@ -1,17 +1,24 @@
 name = "RegisterUtilities"
 uuid = "d4862ba2-f42c-5aeb-af4f-96a8884a16c4"
+version = "1.0.0"
 authors = ["Tim Holy <tim.holy@gmail.com>"]
-version = "0.1.0"
 
 [deps]
 LinearAlgebra = "37e2e46d-f89d-539d-b4ee-838fcccc9c8e"
 RegisterCore = "67712758-55e7-5c3c-8e85-dda1d7758434"
 
 [compat]
-julia = "^1.1"
+Aqua = "0.8"
+ExplicitImports = "1"
+LinearAlgebra = "1"
+RegisterCore = "0.2"
+Test = "1"
+julia = "1.10"
 
 [extras]
+Aqua = "4c88cf16-eb10-579e-8560-4a9242c79595"
+ExplicitImports = "7d51a73a-1435-4ff3-83d9-f097790105c7"
 Test = "8dfed614-e22c-5e08-85e1-65c5234f0b40"
 
 [targets]
-test = ["Test"]
+test = ["Aqua", "ExplicitImports", "Test"]
diff --git a/README.md b/README.md
new file mode 100644
index 0000000..09d1209
--- /dev/null
+++ b/README.md
@@ -0,0 +1,80 @@
+# RegisterUtilities.jl
+
+[![CI](https://github.com/HolyLab/RegisterUtilities.jl/actions/workflows/CI.yml/badge.svg)](https://github.com/HolyLab/RegisterUtilities.jl/actions/workflows/CI.yml)
+[![codecov](https://codecov.io/gh/HolyLab/RegisterUtilities.jl/branch/master/graph/badge.svg)](https://codecov.io/gh/HolyLab/RegisterUtilities.jl)
+[![version](https://juliahub.com/docs/General/RegisterUtilities/stable/version.svg)](https://juliahub.com/ui/Packages/General/RegisterUtilities)
+
+Utility types and functions for image-registration workflows in the
+[HolyLab](https://github.com/HolyLab) ecosystem.
+
+## Installation
+
+This package depends on
+[RegisterCore.jl](https://github.com/HolyLab/RegisterCore.jl), which lives in
+the [HolyLab registry](https://github.com/HolyLab/HolyLabRegistry). Add that
+registry once before installing:
+
+```julia
+using Pkg
+pkg"registry add General https://github.com/HolyLab/HolyLabRegistry.git"
+Pkg.add("RegisterUtilities")
+```
+
+## Usage
+
+### `Counter` — column-major multi-dimensional index iterator
+
+`Counter` yields every `Vector{Int}` index from `[1,1,…,1]` to `max` in
+column-major (first-index-fastest) order. Unlike `CartesianIndices`, the
+yielded values are plain vectors, which is convenient for arithmetic.
+
+```julia
+using RegisterUtilities
+
+c = Counter((2, 3))
+collect(c)
+# [[1,1],[2,1],[1,2],[2,2],[1,3],[2,3]]
+
+length(Counter((4, 5, 6)))  # 120
+```
+
+### `block_center` — center coordinate of a block
+
+Returns the 1-based center of a block with the given dimensions, using the
+same convention as `MismatchArray` blocks: center of dimension `i` is
+`(sz[i] >> 1) + 1`.
+
+```julia
+block_center(5)       # (3,)
+block_center(4, 6)    # (3, 4)
+block_center(5, 5, 5) # (3, 3, 3)
+```
+
+### `quadratic` — quadratic-form array
+
+Fills a 2-D array where each element `(i,j)` equals `uᵀ Q u`, with
+`u = [i,j] - center` and `center = block_center(m,n) .+ shift`. The second
+method wraps the result in a `MismatchArray` with a given denominator.
+
+```julia
+using RegisterUtilities, LinearAlgebra
+
+Q = [1.0 0.0; 0.0 1.0]   # identity — distance² from center
+A = quadratic(5, 5, [0, 0], Q)
+# 5×5 matrix of squared distances from the block center (3, 3)
+
+using RegisterCore
+denom = ones(5, 5)
+ma = quadratic(denom, [0, 0], Q)   # returns a MismatchArray
+```
+
+### `tighten` — narrow element type
+
+Converts a heterogeneous or overly-wide array (e.g. `Array{Real}`) to the
+narrowest concrete type that holds all its values.
+
+```julia
+A = Real[1, 2.0, 3f0]
+B = tighten(A)
+eltype(B)   # Float64
+```
diff --git a/src/RegisterUtilities.jl b/src/RegisterUtilities.jl
index c670395..8a27ee8 100644
--- a/src/RegisterUtilities.jl
+++ b/src/RegisterUtilities.jl
@@ -1,22 +1,53 @@
+"""
+    RegisterUtilities
+
+Utility types and functions for image-registration workflows.
+
+Exports:
+- [`Counter`](@ref): column-major multi-dimensional index iterator.
+- [`quadratic`](@ref): construct a quadratic-form array or `MismatchArray`.
+- [`block_center`](@ref): compute the center coordinate of a block.
+- [`tighten`](@ref): narrow an array to its tightest concrete element type.
+"""
 module RegisterUtilities
 
 export Counter
 
-#### Counter ####
-#
-# Stolen from Grid.jl. Useful when you want to do more math on the iterator.
+"""
+    Counter(max::AbstractVector{<:Integer})
+    Counter(sz::Tuple)
+
+An iterator that yields every `Vector{Int}` index tuple from `[1, 1, …, 1]`
+to `max` (or `collect(sz)`), traversing in column-major (first-index-fastest)
+order.
+
+Unlike `CartesianIndices`, `Counter` yields plain `Vector{Int}` values, making
+it convenient when the index needs to be used in arithmetic expressions.
+
+`length(c)` returns the total number of elements (`prod(max)`), or `0` if any
+dimension is ≤ 0.
 
+# Examples
+```julia
+c = Counter((2, 3))
+collect(c)  # [[1,1],[2,1],[1,2],[2,2],[1,3],[2,3]]
+```
+"""
 struct Counter
     max::Vector{Int}
 end
 Counter(sz::Tuple) = Counter(Int[sz...])
+Counter(max::AbstractVector{<:Integer}) = Counter(convert(Vector{Int}, max))
+
+Base.length(c::Counter) = isempty(c.max) || any(<=(0), c.max) ? 0 : prod(c.max)
+
 function Base.iterate(c::Counter)
     N = length(c.max)
     (N == 0 || any(c.max .<= 0)) && return nothing
     state = ones(Int, N)
     return copy(state), state
 end
-function Base.iterate(c::Counter, state)
+function Base.iterate(c::Counter, state::Vector{Int})
     state[1] += 1
     i = 1
     while state[i] > c.max[i] && i < length(state)
@@ -30,15 +61,37 @@ end
 
 # Below functions are from RegisterTestUtilities
 
-using RegisterCore, LinearAlgebra
+using LinearAlgebra: LinearAlgebra, dot
+using RegisterCore: RegisterCore, MismatchArray
 
 export quadratic, block_center, tighten
 
+"""
+    quadratic(m, n, shift, Q)
+    quadratic(denom::AbstractMatrix, shift, Q)
+
+Construct a 2-D array of quadratic-form values centered at a shifted block
+center.
+
+For each pixel `(i, j)` the value is `uᵀ Q u`, where `u = [i, j] - center`
+and `center = block_center(m, n) .+ shift`.
+
+The second method wraps the result in a `MismatchArray` using `denom` as the
+denominator array; `m` and `n` are taken from `size(denom)`.
+
+# Arguments
+- `m`, `n`: output array dimensions (rows, columns).
+- `denom`: an existing `AbstractMatrix` whose size sets the output dimensions
+  and whose values become the denominator of the returned `MismatchArray`.
+- `shift`: 2-element offset added to the block center.
+- `Q`: 2×2 matrix defining the quadratic form.
+"""
 function quadratic(m, n, shift, Q)
-    A = zeros(m, n)
+    T = float(eltype(Q))
+    A = zeros(T, m, n)
     c = block_center(m, n)
     cntr = [shift[1] + c[1], shift[2] + c[2]]
-    u = zeros(2)
+    u = zeros(T, 2)
     for j in 1:n, i in 1:m
         u[1], u[2] = i - cntr[1], j - cntr[2]
         A[i, j] = dot(u, Q * u)
@@ -46,12 +99,45 @@ function quadratic(m, n, shift, Q)
     return A
 end
 
-quadratic(shift, Q, denom::Matrix) = MismatchArray(quadratic(size(denom)..., shift, Q), denom)
+quadratic(denom::AbstractMatrix, shift, Q) = MismatchArray(quadratic(size(denom)..., shift, Q), denom)
+
+"""
+    block_center(sz...)
+
+Return the 1-based center coordinate of a block with dimensions `sz` as an
+`NTuple`.
 
+The center of dimension `i` is computed as `(sz[i] >> 1) + 1`, matching the
+convention used by `MismatchArray` blocks.
+
+# Examples
+```julia
+block_center(5)       # (3,)
+block_center(4, 6)    # (3, 4)
+block_center(5, 5, 5) # (3, 3, 3)
+```
+"""
 function block_center(sz...)
-    return ntuple(i -> sz[i] >> 1 + 1, length(sz))
+    return ntuple(i -> (sz[i] >> 1) + 1, length(sz))
 end
 
+"""
+    tighten(A::AbstractArray)
+
+Return a copy of `A` with the narrowest element type that can hold all of its
+values.
+
+Iterates over every element of `A` and accumulates a common type via
+`promote_type`, then copies `A` into a new array of that type.  Useful for
+converting heterogeneous or overly-wide arrays (e.g. `Array{Real}`) into a
+concrete, efficient representation.
+
+# Example
+```julia
+A = Real[1, 2.0, 3f0]   # element type Real
+B = tighten(A)           # element type Float64
+```
+"""
 function tighten(A::AbstractArray)
     T = typeof(first(A))
     for a in A
diff --git a/test/runtests.jl b/test/runtests.jl
index dc401c6..f81eb23 100644
--- a/test/runtests.jl
+++ b/test/runtests.jl
@@ -1,6 +1,18 @@
 using Test
+using Aqua
+using ExplicitImports
+using LinearAlgebra: I
+using RegisterCore: RegisterCore
 using RegisterUtilities
 
+@testset "Aqua" begin
+    Aqua.test_all(RegisterUtilities)
+end
+
+@testset "ExplicitImports" begin
+    test_explicit_imports(RegisterUtilities)
+end
+
 @testset "Counter test" begin
     for empty_gridsize in ((), (0,), (1, 0), (1, -1), (1, 0, 1))
         for c in Counter(empty_gridsize)
@@ -24,4 +36,50 @@ using RegisterUtilities
         end
         @test cnt == index_vec
     end
+    # AbstractVector constructor
+    cnt32 = [c for c in Counter(Int32[2, 3])]
+    @test cnt32 == [[1,1],[2,1],[1,2],[2,2],[1,3],[2,3]]
+end
+
+@testset "block_center" begin
+    @test block_center(1) == (1,)
+    @test block_center(2) == (2,)
+    @test block_center(4) == (3,)
+    @test block_center(5) == (3,)
+    @test block_center(4, 6) == (3, 4)
+    @test block_center(8) == (5,)
+end
+
+@testset "quadratic" begin
+    Q = Matrix(1.0I, 2, 2)
+    m, n = 5, 7
+    A = quadratic(m, n, (0, 0), Q)
+    @test size(A) == (m, n)
+    c = block_center(m, n)
+    @test A[c...] == 0.0
+    @test all(>=(0), A)
+    @inferred quadratic(m, n, (0, 0), Q)
+
+    # shifting the center moves the zero
+    A2 = quadratic(m, n, (1, 0), Q)
+    @test A2[c[1] + 1, c[2]] == 0.0
+
+    # matrix-denom variant returns a MismatchArray of the right size
+    denom = ones(m, n)
+    result = quadratic(denom, (0, 0), Q)
+    @test result isa RegisterCore.MismatchArray
+    @test size(result) == (m, n)
+end
+
+@testset "tighten" begin
+    # heterogeneous Any-array gets promoted
+    A = Any[1, 2.0, 3f0]
+    result = tighten(A)
+    @test eltype(result) == Float64
+    @test result ≈ [1.0, 2.0, 3.0]
+
+    # already-concrete array is unchanged in value and type
+    B = [1, 2, 3]
+    @test tighten(B) == B
+    @test eltype(tighten(B)) == Int
 end