diff --git a/hammer_ir/scalalib/.gitignore b/hammer_ir/scalalib/.gitignore
new file mode 100644
index 000000000..b6ae9c889
--- /dev/null
+++ b/hammer_ir/scalalib/.gitignore
@@ -0,0 +1,5 @@
+out/
+*.jar
+amm
+mill
+test/tmp_*
diff --git a/hammer_ir/scalalib/README.md b/hammer_ir/scalalib/README.md
new file mode 100644
index 000000000..614f62824
--- /dev/null
+++ b/hammer_ir/scalalib/README.md
@@ -0,0 +1,9 @@
+Hammer IR Scala library
+=======================
+
+This API is experimental and subject to change at any time.
+
+To get a JAR, run `./build.sh`.
+You can find the output JAR in `out/hammer_ir/assembly/dest/out.jar`.
+
+TODO(edwardw): write documentation for what this is and how to use it.
diff --git a/hammer_ir/scalalib/build.sc b/hammer_ir/scalalib/build.sc
new file mode 100644
index 000000000..f40b49ea9
--- /dev/null
+++ b/hammer_ir/scalalib/build.sc
@@ -0,0 +1,17 @@
+import mill._, scalalib._
+
+object hammer_ir extends SbtModule {
+  def scalaVersion = "2.12.6"
+
+  // Unrooted submodule
+  override def millSourcePath = super.millSourcePath / ammonite.ops.up
+
+  def ivyDeps = Agg(
+    ivy"com.typesafe.play::play-json:2.6.10"
+  )
+
+  object test extends Tests {
+    def ivyDeps = Agg(ivy"org.scalatest::scalatest:3.0.4")
+    def testFrameworks = Seq("org.scalatest.tools.Framework")
+  }
+}
diff --git a/hammer_ir/scalalib/build.sh b/hammer_ir/scalalib/build.sh
new file mode 100755
index 000000000..e856c02c4
--- /dev/null
+++ b/hammer_ir/scalalib/build.sh
@@ -0,0 +1,6 @@
+#!/bin/sh
+if [ ! -f "./mill" ]; then
+  ./get_mill.sh
+fi
+./mill hammer_ir.assembly
+cp out/hammer_ir/assembly/dest/out.jar hammer_ir.jar
diff --git a/hammer_ir/scalalib/get_ammonite.sh b/hammer_ir/scalalib/get_ammonite.sh
new file mode 100755
index 000000000..97186aeee
--- /dev/null
+++ b/hammer_ir/scalalib/get_ammonite.sh
@@ -0,0 +1,4 @@
+#!/bin/sh
+set -ex
+wget -nv https://github.com/lihaoyi/Ammonite/releases/download/1.6.6/2.12-1.6.6 -O amm
+chmod +x ./amm
diff --git a/hammer_ir/scalalib/get_mill.sh b/hammer_ir/scalalib/get_mill.sh
new file mode 100755
index 000000000..7b378225f
--- /dev/null
+++ b/hammer_ir/scalalib/get_mill.sh
@@ -0,0 +1,4 @@
+#!/bin/sh
+set -ex
+wget -nv https://github.com/lihaoyi/mill/releases/download/0.3.6/0.3.6 -O mill
+chmod +x ./mill
diff --git a/hammer_ir/scalalib/scalatest.sh b/hammer_ir/scalalib/scalatest.sh
new file mode 100755
index 000000000..f9833a348
--- /dev/null
+++ b/hammer_ir/scalalib/scalatest.sh
@@ -0,0 +1,2 @@
+#!/bin/sh
+./mill hammer_ir.test
diff --git a/hammer_ir/scalalib/src/main/scala/HammerObject.scala b/hammer_ir/scalalib/src/main/scala/HammerObject.scala
new file mode 100644
index 000000000..25bf1cc6f
--- /dev/null
+++ b/hammer_ir/scalalib/src/main/scala/HammerObject.scala
@@ -0,0 +1,62 @@
+// See LICENSE for licence details.
+
+package hammer_ir
+
+import scala.reflect.ClassTag
+
+import play.api.libs.json.{Json, JsObject, JsValue}
+
+/**
+ * All Hammer IR types that can be converted to a JsValue.
+ */
+trait JSONConvertible {
+  /**
+   * Turn this object into a Play JSON object.
+   */
+  private[hammer_ir] def toJSON: JsValue
+}
+
+/**
+ * All Hammer IR objects implement this trait which allows them to be
+ * serialized to/deserialized from JSON.
+ */
+trait HammerObject {
+  /**
+   * Turn this object into a Play JSON object.
+   */
+  private[hammer_ir] def toJSON: JsObject
+
+  /**
+   * Turn this object into a JSON string.
+   */
+  override def toString = Json.prettyPrint(toJSON)
+
+  /**
+   * Write this object as a JSON string into the given file.
+   */
+  def toFile(filename: String) = reflect.io.File(filename).writeAll(toString)
+}
+
+/**
+ * Abstract class mixed into companion classes of Hammer IR objects.
+ */
+abstract class HammerObjectCompanion[T <: HammerObject : ClassTag] {
+  /**
+   * Create this object from a Play JSON object.
+   */
+  private[hammer_ir] def fromJSON(json: JsObject): T
+
+  /**
+   * Create this object from a JSON string.
+   */
+  def fromString(json: String): T = fromJSON(Json.parse(json).as[JsObject])
+
+  /**
+   * Create this object from a JSON file.
+   */
+  def fromFile(filename: String): T = {
+    val source = scala.io.Source.fromFile(filename)
+    val lines = try source.mkString finally source.close()
+    fromString(lines)
+  }
+}
diff --git a/hammer_ir/scalalib/src/main/scala/PlacementConstraint.scala b/hammer_ir/scalalib/src/main/scala/PlacementConstraint.scala
new file mode 100644
index 000000000..77beefba2
--- /dev/null
+++ b/hammer_ir/scalalib/src/main/scala/PlacementConstraint.scala
@@ -0,0 +1,136 @@
+// See LICENSE for licence details.
+
+package hammer_ir
+
+import play.api.libs.json.{JsNumber, JsObject, JsString}
+
+sealed abstract class PlacementConstraintType extends JSONConvertible {
+  override def toJSON = JsString(stringVal)
+  // Force objects to implement this since toString is defined by
+  // default.
+  def stringVal: String
+  override def toString = stringVal
+}
+object PlacementConstraintType {
+  def fromString(input: String): PlacementConstraintType = {
+    values.foreach { i =>
+      if (i.stringVal == input) return i
+    }
+    throw new IllegalArgumentException(s"Illegal PlacementConstraintType $input")
+  }
+
+  case object Dummy extends PlacementConstraintType {
+    override def stringVal = "dummy"
+  }
+  case object Placement extends PlacementConstraintType {
+    override def stringVal = "placement"
+  }
+  case object TopLevel extends PlacementConstraintType {
+    override def stringVal = "toplevel"
+  }
+  case object HardMacro extends PlacementConstraintType {
+    override def stringVal = "hardmacro"
+  }
+  case object Hierarchical extends PlacementConstraintType {
+    override def stringVal = "hierarchical"
+  }
+  case object Obstruction extends PlacementConstraintType {
+    override def stringVal = "obstruction"
+  }
+
+  def values = Seq(
+    Dummy, Placement, TopLevel, HardMacro, Hierarchical, Obstruction
+  )
+}
+
+sealed abstract class ObstructionType
+object ObstructionType {
+  case object Place extends ObstructionType
+  case object Route extends ObstructionType
+  case object Power extends ObstructionType
+}
+
+case class Margins(
+  left: Double,
+  bottom: Double,
+  right: Double,
+  top: Double
+)
+
+case class PlacementConstraint(
+  path: String,
+  `type`: PlacementConstraintType,
+  x: Double,
+  y: Double,
+  width: Double,
+  height: Double,
+  orientation: Option[String],
+  margins: Option[Margins],
+  top_layer: Option[String],
+  layers: Option[Seq[String]],
+  obs_types: Option[Seq[ObstructionType]]
+) extends HammerObject {
+  override def toJSON = {
+    JsObject(Seq(
+      "path" -> JsString(path),
+      "type" -> `type`.toJSON,
+      "x" -> JsNumber(x),
+      "y" -> JsNumber(y),
+      "width" -> JsNumber(width),
+      "height" -> JsNumber(height)
+      // TODO(edwardw): FIXME
+    ))
+  }
+}
+
+object PlacementConstraint extends HammerObjectCompanion[PlacementConstraint] {
+  def apply(
+    path: String,
+    `type`: PlacementConstraintType,
+    x: Double,
+    y: Double,
+    width: Double,
+    height: Double
+  ): PlacementConstraint = {
+    new PlacementConstraint(
+      path,
+      `type`,
+      x,
+      y,
+      width,
+      height,
+      None, // TODO(edwardw): FIXME
+      None,
+      None,
+      None,
+      None
+    )
+  }
+
+  /* Helper function used to convert strings to Double
+   * for forwards-compatibility with Decimal type. */
+  def doubleOrString(value: play.api.libs.json.JsLookupResult): Double = {
+    try {
+      value.as[Double]
+    } catch {
+      case _: play.api.libs.json.JsResultException =>
+        value.as[String].toDouble
+    }
+  }
+
+  override def fromJSON(json: JsObject): PlacementConstraint = {
+    new PlacementConstraint(
+      (json \ "path").as[String],
+      PlacementConstraintType.fromString((json \ "type").as[String]),
+      doubleOrString(json \ "x"),
+      doubleOrString(json \ "y"),
+      doubleOrString(json \ "width"),
+      doubleOrString(json \ "height"),
+      None, // TODO(edwardw): FIXME
+      None,
+      None,
+      None,
+      None
+    )
+  }
+}
diff --git a/hammer_ir/scalalib/src/test/scala/HammerObjectSpec.scala b/hammer_ir/scalalib/src/test/scala/HammerObjectSpec.scala
new file mode 100644
index 000000000..13562bbb6
--- /dev/null
+++ b/hammer_ir/scalalib/src/test/scala/HammerObjectSpec.scala
@@ -0,0 +1,34 @@
+// See LICENSE for licence details.
+
+package hammer_ir.test
+
+import org.scalatest.{FlatSpec, Matchers}
+import play.api.libs.json.{JsObject, JsString}
+
+import hammer_ir._
+
+class HammerObjectSpec extends FlatSpec with Matchers {
+  behavior of "HammerObject"
+
+  case class Test(foobar: String) extends HammerObject {
+    override def toJSON = JsObject(Seq(
+      "foobar" -> JsString(foobar)
+    ))
+  }
+  object Test extends HammerObjectCompanion[Test] {
+    override def fromJSON(json: JsObject): Test = {
+      new Test(
+        (json \ "foobar").as[String]
+      )
+    }
+  }
+
+  it should "serialize and deserialize correctly" in {
+    val t = Test("helloworld")
+    // Need these replaces to be robust to spacing variations
+    assert(t.toString
+      .replaceAll("\n", "").replaceAll(" ", "")
+      === """{"foobar":"helloworld"}""")
+    assert(Test.fromJSON(t.toJSON) == t)
+  }
+}
diff --git a/hammer_ir/scalalib/test/placement_test/script.scala b/hammer_ir/scalalib/test/placement_test/script.scala
new file mode 100644
index 000000000..506f8060b
--- /dev/null
+++ b/hammer_ir/scalalib/test/placement_test/script.scala
@@ -0,0 +1,15 @@
+// See LICENSE for licence details.
+
+import $cp.`hammer_ir.jar`
+
+import hammer_ir._
+
+// Read and write back
+val p = PlacementConstraint.fromFile("c1.json")
+
+p.`type` match {
+  case PlacementConstraintType.Placement => println("Am placement")
+  case _ => println("Am not placement")
+}
+
+p.toFile("c1-out.json")
diff --git a/hammer_ir/scalalib/test/prep.sh b/hammer_ir/scalalib/test/prep.sh
new file mode 100755
index 000000000..9700ffef4
--- /dev/null
+++ b/hammer_ir/scalalib/test/prep.sh
@@ -0,0 +1,24 @@
+#!/bin/bash
+# Test preparation script.
+# Ensures that ammonite and the Hammer IR JAR are built.
+
+set -e
+set -euo pipefail
+
+script_dir=$(dirname $0)
+cd $script_dir
+
+# Build Hammer IR
+pushd ..
+./build.sh
+
+# Ensure ammonite exists
+if [ ! -f "amm" ]; then
+  ./get_ammonite.sh
+fi
+
+popd
+
+# Create ammonite wrapper to import hammer_ir JAR.
+echo "../amm --predef-code 'import ammonite.ops._; interp.load.cp(pwd/os.up/\"hammer_ir.jar\")' \$1" > amm
+chmod +x amm
diff --git a/hammer_ir/scalalib/test/run_tests.sh b/hammer_ir/scalalib/test/run_tests.sh
new file mode 100755
index 000000000..efc83447d
--- /dev/null
+++ b/hammer_ir/scalalib/test/run_tests.sh
@@ -0,0 +1,4 @@
+#!/bin/sh
+set -ex
+cd $(dirname $0)
+./test_*
diff --git a/hammer_ir/scalalib/test/test_placement.py b/hammer_ir/scalalib/test/test_placement.py
new file mode 100755
index 000000000..f37fcfbf1
--- /dev/null
+++ b/hammer_ir/scalalib/test/test_placement.py
@@ -0,0 +1,81 @@
+#!/usr/bin/env python3
+# -*- coding: utf-8 -*-
+#
+#  Test placement constraints in Hammer IR.
+#
+#  See LICENSE for licence details.
+
+import json
+import os
+import sys
+
+# TODO(edwardw): separate hammer_ir out of hammer_vlsi
+from hammer_vlsi import PlacementConstraint, PlacementConstraintType
+
+# TODO(edwardw): move these to a separate file/library
+prepped = False  # type: bool
+def prep() -> None:
+    assert os.system("./prep.sh") == 0
+    global prepped
+    prepped = True
+
+def run_scala(scala: str) -> None:
+    assert prepped, "Must prep before running test functions"
+
+    with open("tmp_script.scala", "w") as f:
+        f.write(scala)
+
+    if os.system("./amm tmp_script.scala") != 0:
+        print("Scala script below failed: \n{}".format(scala), file=sys.stderr)
+        sys.exit(1)
+
+prep()
+
+# Generate some constraints
+c1 = PlacementConstraint(
+    path="Top/rtl/a/b",
+    type=PlacementConstraintType.Placement,
+    x=15.123,
+    y=14.567,
+    width=42.900,
+    height=888.100,
+    orientation=None,
+    margins=None,
+    top_layer=None,
+    layers=None,
+    obs_types=None
+)
+
+# TODO(edwardw): the optional parameters are only valid for certain
+# types of constraints.
+# e.g. orientation is only valid for hardmacros
+# e.g. obs_types is only valid for obstructions
+# We need to create some extra testcases to capture those usecases.
+
+# Export to JSON
+with open("tmp_c1.json", "w") as f:
+    f.write(json.dumps(c1.to_dict()))
+
+# Check that it's still usable in Scala-land
+run_scala("""
+import hammer_ir._
+
+// Read and write back
+val p = PlacementConstraint.fromFile("tmp_c1.json")
+
+assert(p.path == "Top/rtl/a/b")
+assert(p.`type` == PlacementConstraintType.Placement)
+assert(p.x == 15.123)
+assert(p.y == 14.567)
+assert(p.width == 42.900)
+assert(p.height == 888.100)
+
+p.toFile("tmp_c1-out.json")
+""")
+
+# Check that it's still the same
+with open("tmp_c1-out.json", "r") as f:
+    c1_out = PlacementConstraint.from_dict(json.loads(f.read()))
+
+print(c1_out)
+assert c1 == c1_out
diff --git a/src/test/mypy.sh b/src/test/mypy.sh
index 4c6d166d9..c4b3345ba 100755
--- a/src/test/mypy.sh
+++ b/src/test/mypy.sh
@@ -37,6 +37,9 @@ call_mypy ../hammer-vlsi/par/mockpar/__init__.py
 call_mypy ../hammer-vlsi/drc/*.py
 call_mypy ../hammer-vlsi/lvs/*.py
 
+# Scala library
+call_mypy ../../hammer_ir/scalalib/test/*.py
+
 # Plugins which may or may not exist
 if [ -f ../hammer-vlsi/synthesis/dc/__init__.py ]; then
     call_mypy ../hammer-vlsi/synthesis/dc/__init__.py