new file mode 100644
--- /dev/null
+++ b/build/toolchains/README.md
@@ -0,0 +1,8 @@
+# Toolchain Definitions
+
+This directory contains definitions of toolchains used in automation.
+
+The content of these files are turned into Taskclutser tasks by the taskgraph
+generation, and in particular by the toolchain kind, defined in
+`taskcluster/ci/toolchain`.  The format of each stanza in the files here is
+defined in `taskcluster/taskgraph/transforms/toolchain.py.

--- a/build/toolchains/linux.yml
+++ b/build/toolchains/linux.yml
@@ -1,230 +1,152 @@
 # This Source Code Form is subject to the terms of the Mozilla Public
 # License, v. 2.0. If a copy of the MPL was not distributed with this
 # file, You can obtain one at http://mozilla.org/MPL/2.0/.
 
 linux64-clang-3.9:
     description: "Clang 3.9 toolchain build"
-    treeherder:
-        kind: build
-        platform: toolchains/opt
-        symbol: TL(clang3.9)
-        tier: 1
-    worker-type: aws-provisioner-v1/gecko-{level}-b-linux
-    worker:
-        docker-image: {in-tree: desktop-build}
-        max-run-time: 36000
+    symbol: TL(clang3.9)
+    run-on: linux
     run:
         using: toolchain-script
         script: build-clang-3.9-linux.sh
-        resources:
-            - 'build/build-clang/build-clang.py'
-            - 'build/build-clang/clang-3.9-linux64.json'
-            - 'taskcluster/scripts/misc/tooltool-download.sh'
-        toolchain-alias: linux64-clang
-        toolchain-artifact: public/build/clang.tar.xz
+    resources:
+        - 'build/build-clang/build-clang.py'
+        - 'build/build-clang/clang-3.9-linux64.json'
+        - 'taskcluster/scripts/misc/tooltool-download.sh'
+    toolchain-alias: linux64-clang
+    toolchain-artifact: public/build/clang.tar.xz
     toolchains:
         - linux64-gcc-4.9
 
 linux64-clang-4:
     description: "Clang 4 toolchain build"
-    treeherder:
-        kind: build
-        platform: toolchains/opt
-        symbol: TL(clang4)
-        tier: 1
-    worker-type: aws-provisioner-v1/gecko-{level}-b-linux
-    worker:
-        docker-image: {in-tree: desktop-build}
-        max-run-time: 36000
+    symbol: TL(clang4)
+    run-on: linux
     run:
         using: toolchain-script
         script: build-clang-4-linux.sh
-        resources:
-            - 'build/build-clang/build-clang.py'
-            - 'build/build-clang/clang-4-linux64.json'
-            - 'taskcluster/scripts/misc/tooltool-download.sh'
-        toolchain-artifact: public/build/clang.tar.xz
+    resources:
+        - 'build/build-clang/build-clang.py'
+        - 'build/build-clang/clang-4-linux64.json'
+        - 'taskcluster/scripts/misc/tooltool-download.sh'
+    toolchain-artifact: public/build/clang.tar.xz
     toolchains:
         - linux64-gcc-4.9
 
 linux64-clang-tidy:
     description: "Clang-tidy build"
     index:
         product: static-analysis
         job-name: linux64-clang-tidy
-    treeherder:
-        kind: build
-        platform: toolchains/opt
-        symbol: TL(clang-tidy)
-        tier: 1
-    worker-type: aws-provisioner-v1/gecko-{level}-b-linux
-    worker:
-        docker-image: {in-tree: desktop-build}
-        max-run-time: 36000
+    symbol: TL(clang-tidy)
+    run-on: linux
     run:
         using: toolchain-script
         script: build-clang-tidy-linux.sh
-        resources:
-            - 'build/clang-plugin/**'
-            - 'build/build-clang/build-clang.py'
-            - 'build/build-clang/clang-tidy-linux64.json'
-            - 'taskcluster/scripts/misc/tooltool-download.sh'
-        toolchain-artifact: public/build/clang-tidy.tar.xz
+    resources:
+        - 'build/clang-plugin/**'
+        - 'build/build-clang/build-clang.py'
+        - 'build/build-clang/clang-tidy-linux64.json'
+        - 'taskcluster/scripts/misc/tooltool-download.sh'
+    toolchain-artifact: public/build/clang-tidy.tar.xz
     toolchains:
         - linux64-gcc-4.9
 
 linux64-gcc-4.9:
     description: "GCC 4.9 toolchain build"
-    treeherder:
-        kind: build
-        platform: toolchains/opt
-        symbol: TL(gcc4.9)
-        tier: 1
-    worker-type: aws-provisioner-v1/gecko-{level}-b-linux
-    worker:
-        docker-image: {in-tree: desktop-build}
-        max-run-time: 36000
+    symbol: TL(gcc4.9)
+    run-on: linux
     run:
         using: toolchain-script
         script: build-gcc-4.9-linux.sh
-        resources:
-            - 'build/unix/build-gcc/build-gcc.sh'
-        toolchain-artifact: public/build/gcc.tar.xz
+    resources:
+        - 'build/unix/build-gcc/build-gcc.sh'
+    toolchain-artifact: public/build/gcc.tar.xz
 
 linux64-gcc-6:
     description: "GCC 6 toolchain build"
-    treeherder:
-        kind: build
-        platform: toolchains/opt
-        symbol: TL(gcc6)
-        tier: 1
-    worker-type: aws-provisioner-v1/gecko-{level}-b-linux
-    worker:
-        docker-image: {in-tree: desktop-build}
-        max-run-time: 36000
+    symbol: TL(gcc6)
+    run-on: linux
     run:
         using: toolchain-script
         script: build-gcc-6-linux.sh
-        resources:
-            - 'build/unix/build-gcc/build-gcc.sh'
-        toolchain-alias: linux64-gcc
-        toolchain-artifact: public/build/gcc.tar.xz
+    resources:
+        - 'build/unix/build-gcc/build-gcc.sh'
+    toolchain-alias: linux64-gcc
+    toolchain-artifact: public/build/gcc.tar.xz
 
 linux64-binutils:
     description: "Binutils toolchain build"
-    treeherder:
-        kind: build
-        platform: toolchains/opt
-        symbol: TL(binutil)
-        tier: 1
-    worker-type: aws-provisioner-v1/gecko-{level}-b-linux
-    worker:
-        docker-image: {in-tree: desktop-build}
-        max-run-time: 36000
+    symbol: TL(binutil)
+    run-on: linux
     run:
         using: toolchain-script
         script: build-binutils-linux.sh
-        resources:
-            - 'build/unix/build-binutils/build-binutils.sh'
-        toolchain-artifact: public/build/binutils.tar.xz
+    resources:
+        - 'build/unix/build-binutils/build-binutils.sh'
+    toolchain-artifact: public/build/binutils.tar.xz
 
 linux64-cctools-port:
     description: "cctools-port toolchain build"
-    treeherder:
-        kind: build
-        platform: toolchains/opt
-        symbol: TL(cctools)
-        tier: 1
-    worker-type: aws-provisioner-v1/gecko-{level}-b-linux
-    worker:
-        docker-image: {in-tree: desktop-build}
-        max-run-time: 36000
+    symbol: TL(cctools)
+    run-on: linux
     run:
         using: toolchain-script
         script: build-cctools-port.sh
-        resources:
-            - 'taskcluster/scripts/misc/tooltool-download.sh'
-        toolchain-artifact: public/build/cctools.tar.xz
+    resources:
+        - 'taskcluster/scripts/misc/tooltool-download.sh'
+    toolchain-artifact: public/build/cctools.tar.xz
     toolchains:
         - linux64-clang-3.9
 
 linux64-hfsplus:
     description: "hfsplus toolchain build"
-    treeherder:
-        kind: build
-        platform: toolchains/opt
-        symbol: TL(hfs+)
-        tier: 1
-    worker-type: aws-provisioner-v1/gecko-{level}-b-linux
-    worker:
-        docker-image: {in-tree: desktop-build}
-        max-run-time: 36000
+    symbol: TL(hfs+)
+    run-on: linux
     run:
         using: toolchain-script
         script: build-hfsplus-linux.sh
-        resources:
-            - 'build/unix/build-hfsplus/build-hfsplus.sh'
-            - 'taskcluster/scripts/misc/tooltool-download.sh'
-        toolchain-artifact: public/build/hfsplus-tools.tar.xz
+    resources:
+        - 'build/unix/build-hfsplus/build-hfsplus.sh'
+        - 'taskcluster/scripts/misc/tooltool-download.sh'
+    toolchain-artifact: public/build/hfsplus-tools.tar.xz
     toolchains:
         - linux64-clang-3.9
 
 linux64-libdmg:
     description: "libdmg-hfsplus toolchain build"
-    treeherder:
-        kind: build
-        platform: toolchains/opt
-        symbol: TL(libdmg-hfs+)
-        tier: 1
-    worker-type: aws-provisioner-v1/gecko-{level}-b-linux
-    worker:
-        docker-image: {in-tree: desktop-build}
-        max-run-time: 36000
+    symbol: TL(libdmg-hfs+)
+    run-on: linux
     run:
         using: toolchain-script
         script: build-libdmg-hfsplus.sh
-        toolchain-artifact: public/build/dmg.tar.xz
+    toolchain-artifact: public/build/dmg.tar.xz
 
 linux64-sccache:
     description: "sccache toolchain build"
-    treeherder:
-        kind: build
-        platform: toolchains/opt
-        symbol: TL(sccache)
-        tier: 1
-    worker-type: aws-provisioner-v1/gecko-{level}-b-linux
-    worker:
-        docker-image: {in-tree: desktop-build}
-        max-run-time: 36000
-        env:
-            TOOLTOOL_MANIFEST: "browser/config/tooltool-manifests/linux64/releng.manifest"
+    symbol: TL(sccache)
+    run-on: linux
+    tooltool-manifest: "browser/config/tooltool-manifests/linux64/releng.manifest"
     run:
         using: toolchain-script
         script: build-sccache.sh
-        resources:
-            - 'taskcluster/scripts/misc/tooltool-download.sh'
-        toolchain-artifact: public/build/sccache2.tar.xz
+    resources:
+        - 'taskcluster/scripts/misc/tooltool-download.sh'
+    toolchain-artifact: public/build/sccache2.tar.xz
     toolchains:
         - linux64-clang-3.9
 
 linux64-gn:
     description: "gn toolchain build"
-    treeherder:
-        kind: build
-        platform: toolchains/opt
-        symbol: TL(gn)
-        tier: 1
-    worker-type: aws-provisioner-v1/gecko-{level}-b-linux
-    worker:
-        docker-image: {in-tree: desktop-build}
-        max-run-time: 36000
+    symbol: TL(gn)
+    run-on: linux
     run:
         using: toolchain-script
         script: build-gn-linux.sh
         tooltool-downloads: public
-        resources:
-            - 'taskcluster/scripts/misc/tooltool-download.sh'
-            - 'taskcluster/scripts/misc/build-gn-common.sh'
-        toolchain-artifact: public/build/gn.tar.xz
+    resources:
+        - 'taskcluster/scripts/misc/tooltool-download.sh'
+        - 'taskcluster/scripts/misc/build-gn-common.sh'
+    toolchain-artifact: public/build/gn.tar.xz
     toolchains:
         - linux64-gcc-4.9

--- a/build/toolchains/macosx.yml
+++ b/build/toolchains/macosx.yml
@@ -1,110 +1,78 @@
 # This Source Code Form is subject to the terms of the Mozilla Public
 # License, v. 2.0. If a copy of the MPL was not distributed with this
 # file, You can obtain one at http://mozilla.org/MPL/2.0/.
 
 macosx64-clang:
     description: "Clang toolchain build"
-    treeherder:
-        kind: build
-        platform: toolchains/opt
-        symbol: TM(clang)
-        tier: 1
-    worker-type: aws-provisioner-v1/gecko-{level}-b-macosx64
-    worker:
-        docker-image: {in-tree: desktop-build}
-        max-run-time: 36000
-        env:
-            TOOLTOOL_MANIFEST: "browser/config/tooltool-manifests/macosx64/cross-clang.manifest"
+    symbol: TM(clang)
+    run-on: macosx-cross
+    tooltool-manifest: "browser/config/tooltool-manifests/macosx64/cross-clang.manifest"
     run:
         using: toolchain-script
         script: build-clang-macosx.sh
         tooltool-downloads: internal
-        resources:
-            - 'build/build-clang/build-clang.py'
-            - 'build/build-clang/clang-macosx64.json'
-            - 'taskcluster/scripts/misc/tooltool-download.sh'
-        toolchain-artifact: public/build/clang.tar.xz
+    resources:
+        - 'build/build-clang/build-clang.py'
+        - 'build/build-clang/clang-macosx64.json'
+        - 'taskcluster/scripts/misc/tooltool-download.sh'
+    toolchain-artifact: public/build/clang.tar.xz
     toolchains:
         - linux64-cctools-port
         - linux64-clang-3.9
         - linux64-gcc-4.9
 
 macosx64-clang-tidy:
     description: "Clang-tidy build"
     index:
         product: static-analysis
         job-name: macosx64-clang-tidy
-    treeherder:
-        kind: build
-        platform: toolchains/opt
-        symbol: TM(clang-tidy)
-        tier: 1
-    worker-type: aws-provisioner-v1/gecko-{level}-b-macosx64
-    worker:
-        docker-image: {in-tree: desktop-build}
-        max-run-time: 36000
-        env:
-            TOOLTOOL_MANIFEST: "browser/config/tooltool-manifests/macosx64/cross-clang.manifest"
+    symbol: TM(clang-tidy)
+    run-on: macosx-cross
+    tooltool-manifest: "browser/config/tooltool-manifests/macosx64/cross-clang.manifest"
     run:
         using: toolchain-script
         script: build-clang-tidy-macosx.sh
         tooltool-downloads: internal
-        resources:
-            - 'build/clang-plugin/**'
-            - 'build/build-clang/build-clang.py'
-            - 'build/build-clang/clang-tidy-macosx64.json'
-            - 'taskcluster/scripts/misc/tooltool-download.sh'
-        toolchain-artifact: public/build/clang-tidy.tar.xz
+    resources:
+        - 'build/clang-plugin/**'
+        - 'build/build-clang/build-clang.py'
+        - 'build/build-clang/clang-tidy-macosx64.json'
+        - 'taskcluster/scripts/misc/tooltool-download.sh'
+    toolchain-artifact: public/build/clang-tidy.tar.xz
     toolchains:
         - linux64-cctools-port
         - linux64-clang-3.9
         - linux64-gcc-4.9
 
 macosx64-cctools-port:
     description: "cctools-port toolchain build"
-    treeherder:
-        kind: build
-        platform: toolchains/opt
-        symbol: TM(cctools)
-        tier: 1
-    worker-type: aws-provisioner-v1/gecko-{level}-b-macosx64
-    worker:
-        docker-image: {in-tree: desktop-build}
-        max-run-time: 36000
-        env:
-            TOOLTOOL_MANIFEST: "browser/config/tooltool-manifests/macosx64/cross-clang.manifest"
+    symbol: TM(cctools)
+    run-on: macosx-cross
+    tooltool-manifest: "browser/config/tooltool-manifests/macosx64/cross-clang.manifest"
     run:
         using: toolchain-script
         script: build-cctools-port-macosx.sh
         tooltool-downloads: internal
-        resources:
-            - 'taskcluster/scripts/misc/tooltool-download.sh'
-        toolchain-artifact: public/build/cctools.tar.bz2
+    resources:
+        - 'taskcluster/scripts/misc/tooltool-download.sh'
+    toolchain-artifact: public/build/cctools.tar.bz2
     toolchains:
         - linux64-cctools-port
         - linux64-clang-3.9
 
 macosx64-gn:
     description: "gn toolchain build"
-    treeherder:
-        kind: build
-        platform: toolchains/opt
-        symbol: TM(gn)
-        tier: 1
-    worker-type: aws-provisioner-v1/gecko-{level}-b-macosx64
-    worker:
-        docker-image: {in-tree: desktop-build}
-        max-run-time: 36000
-        env:
-            TOOLTOOL_MANIFEST: "browser/config/tooltool-manifests/macosx64/cross-clang.manifest"
+    symbol: TM(gn)
+    run-on: macosx-cross
+    tooltool-manifest: "browser/config/tooltool-manifests/macosx64/cross-clang.manifest"
     run:
         using: toolchain-script
         script: build-gn-macosx.sh
         tooltool-downloads: internal
-        resources:
-            - 'taskcluster/scripts/misc/tooltool-download.sh'
-            - 'taskcluster/scripts/misc/build-gn-common.sh'
-        toolchain-artifact: public/build/gn.tar.xz
+    resources:
+        - 'taskcluster/scripts/misc/tooltool-download.sh'
+        - 'taskcluster/scripts/misc/build-gn-common.sh'
+    toolchain-artifact: public/build/gn.tar.xz
     toolchains:
         - linux64-cctools-port
         - linux64-clang-3.9

--- a/build/toolchains/windows.yml
+++ b/build/toolchains/windows.yml
@@ -1,134 +1,94 @@
 # This Source Code Form is subject to the terms of the Mozilla Public
 # License, v. 2.0. If a copy of the MPL was not distributed with this
 # file, You can obtain one at http://mozilla.org/MPL/2.0/.
 
 win32-clang-cl:
     description: "Clang-cl toolchain build"
-    treeherder:
-        kind: build
-        platform: toolchains/opt
-        symbol: TW32(clang-cl)
-        tier: 1
-    worker-type: aws-provisioner-v1/gecko-{level}-b-win2012
-    worker:
-        max-run-time: 36000
-        env:
-            TOOLTOOL_MANIFEST: "browser/config/tooltool-manifests/win32/build-clang-cl.manifest"
+    symbol: TW32(clang-cl)
+    run-on: windows
+    tooltool-manifest: "browser/config/tooltool-manifests/win32/build-clang-cl.manifest"
     run:
         using: toolchain-script
         script: build-clang32-windows.sh
-        resources:
-            - 'build/build-clang/build-clang.py'
-            - 'build/build-clang/clang-win32.json'
-            - 'taskcluster/scripts/misc/build-clang-windows-helper32.sh'
-        toolchain-artifact: public/build/clang.tar.bz2
+    resources:
+        - 'build/build-clang/build-clang.py'
+        - 'build/build-clang/clang-win32.json'
+        - 'taskcluster/scripts/misc/build-clang-windows-helper32.sh'
+    toolchain-artifact: public/build/clang.tar.bz2
 
 win64-clang-cl:
     description: "Clang-cl toolchain build"
-    treeherder:
-        kind: build
-        platform: toolchains/opt
-        symbol: TW64(clang-cl)
-        tier: 1
-    worker-type: aws-provisioner-v1/gecko-{level}-b-win2012
-    worker:
-        max-run-time: 36000
-        env:
-            TOOLTOOL_MANIFEST: "browser/config/tooltool-manifests/win32/build-clang-cl.manifest"
+    symbol: TW64(clang-cl)
+    run-on: windows
+    tooltool-manifest: "browser/config/tooltool-manifests/win32/build-clang-cl.manifest"
     run:
         using: toolchain-script
         script: build-clang64-windows.sh
-        resources:
-            - 'build/build-clang/build-clang.py'
-            - 'build/build-clang/clang-win64.json'
-            - 'taskcluster/scripts/misc/build-clang-windows-helper64.sh'
-        toolchain-artifact: public/build/clang.tar.bz2
+    resources:
+        - 'build/build-clang/build-clang.py'
+        - 'build/build-clang/clang-win64.json'
+        - 'taskcluster/scripts/misc/build-clang-windows-helper64.sh'
+    toolchain-artifact: public/build/clang.tar.bz2
 
 win32-clang-tidy:
     description: "Clang-tidy toolchain build"
+    tier: 2
     index:
         product: static-analysis
         job-name: win32-clang-tidy
-    treeherder:
-        kind: build
-        platform: toolchains/opt
-        symbol: TW32(clang-tidy)
-        tier: 2
-    worker-type: aws-provisioner-v1/gecko-{level}-b-win2012
-    worker:
-        max-run-time: 36000
-        env:
-            TOOLTOOL_MANIFEST: "browser/config/tooltool-manifests/win32/build-clang-cl.manifest"
+    symbol: TW32(clang-tidy)
+    run-on: windows
+    tooltool-manifest: "browser/config/tooltool-manifests/win32/build-clang-cl.manifest"
     run:
         using: toolchain-script
         script: build-clang-tidy32-windows.sh
-        resources:
-            - 'build/clang-plugin/**'
-            - 'build/build-clang/build-clang.py'
-            - 'build/build-clang/clang-tidy-win32.json'
-            - 'taskcluster/scripts/misc/build-clang-windows-helper32.sh'
-        toolchain-artifact: public/build/clang-tidy.tar.bz2
+    resources:
+        - 'build/clang-plugin/**'
+        - 'build/build-clang/build-clang.py'
+        - 'build/build-clang/clang-tidy-win32.json'
+        - 'taskcluster/scripts/misc/build-clang-windows-helper32.sh'
+    toolchain-artifact: public/build/clang-tidy.tar.bz2
 
 win64-clang-tidy:
     description: "Clang-tidy toolchain build"
+    tier: 2
     index:
         product: static-analysis
         job-name: win64-clang-tidy
-    treeherder:
-        kind: build
-        platform: toolchains/opt
-        symbol: TW64(clang-tidy)
-        tier: 2
-    worker-type: aws-provisioner-v1/gecko-{level}-b-win2012
-    worker:
-        max-run-time: 36000
-        env:
-            TOOLTOOL_MANIFEST: "browser/config/tooltool-manifests/win32/build-clang-cl.manifest"
+    symbol: TW64(clang-tidy)
+    run-on: windows
+    tooltool-manifest: "browser/config/tooltool-manifests/win32/build-clang-cl.manifest"
     run:
         using: toolchain-script
         script: build-clang-tidy64-windows.sh
-        resources:
-            - 'build/clang-plugin/**'
-            - 'build/build-clang/build-clang.py'
-            - 'build/build-clang/clang-tidy-win32.json'
-            - 'taskcluster/scripts/misc/build-clang-windows-helper64.sh'
-        toolchain-artifact: public/build/clang-tidy.tar.bz2
+    resources:
+        - 'build/clang-plugin/**'
+        - 'build/build-clang/build-clang.py'
+        - 'build/build-clang/clang-tidy-win32.json'
+        - 'taskcluster/scripts/misc/build-clang-windows-helper64.sh'
+    toolchain-artifact: public/build/clang-tidy.tar.bz2
 
 win64-sccache:
     description: "sccache toolchain build"
-    treeherder:
-        kind: build
-        platform: toolchains/opt
-        symbol: TW64(sccache)
-        tier: 1
-    worker-type: aws-provisioner-v1/gecko-{level}-b-win2012
-    worker:
-        max-run-time: 36000
-        env:
-            TOOLTOOL_MANIFEST: "browser/config/tooltool-manifests/win64/sccache-build.manifest"
+    symbol: TW64(sccache)
+    run-on: windows
+    tooltool-manifest: "browser/config/tooltool-manifests/win64/sccache-build.manifest"
     run:
         using: toolchain-script
         script: build-sccache.sh
-        resources:
-            - 'taskcluster/scripts/misc/tooltool-download.sh'
-        toolchain-artifact: public/build/sccache2.tar.bz2
+    resources:
+        - 'taskcluster/scripts/misc/tooltool-download.sh'
+    toolchain-artifact: public/build/sccache2.tar.bz2
 
 win32-gn:
     description: "gn toolchain build"
-    treeherder:
-        kind: build
-        platform: toolchains/opt
-        symbol: TW32(gn)
-        tier: 1
-    worker-type: aws-provisioner-v1/gecko-{level}-b-win2012
-    worker:
-        max-run-time: 36000
-        env:
-            TOOLTOOL_MANIFEST: "browser/config/tooltool-manifests/win32/gn-build.manifest"
+    symbol: TW32(gn)
+    run-on: windows
+    tooltool-manifest: "browser/config/tooltool-manifests/win32/gn-build.manifest"
     run:
         using: toolchain-script
         script: build-gn-win32.sh
-        resources:
-            - 'taskcluster/scripts/misc/tooltool-download.sh'
-            - 'taskcluster/scripts/misc/build-gn-common.sh'
-        toolchain-artifact: public/build/gn.tar.bz2
+    resources:
+        - 'taskcluster/scripts/misc/tooltool-download.sh'
+        - 'taskcluster/scripts/misc/build-gn-common.sh'
+    toolchain-artifact: public/build/gn.tar.bz2

--- a/taskcluster/ci/toolchain/kind.yml
+++ b/taskcluster/ci/toolchain/kind.yml
@@ -1,15 +1,16 @@
 # This Source Code Form is subject to the terms of the Mozilla Public
 # License, v. 2.0. If a copy of the MPL was not distributed with this
 # file, You can obtain one at http://mozilla.org/MPL/2.0/.
 
 loader: taskgraph.loader.transform:loader
 
 transforms:
+   - taskgraph.transforms.toolchain:transforms
    - taskgraph.transforms.try_job:transforms
    - taskgraph.transforms.use_toolchains:transforms
    - taskgraph.transforms.job:transforms
    - taskgraph.transforms.task:transforms
 
 jobs-from:
    - /build/toolchains/linux.yml
    - /build/toolchains/macosx.yml

--- a/taskcluster/taskgraph/transforms/job/toolchain.py
+++ b/taskcluster/taskgraph/transforms/job/toolchain.py
@@ -5,17 +5,17 @@
 Support for running toolchain-building jobs via dedicated scripts
 """
 
 from __future__ import absolute_import, print_function, unicode_literals
 
 import hashlib
 
 from taskgraph.util.schema import Schema
-from voluptuous import Optional, Required, Any
+from voluptuous import Required, Any
 
 from taskgraph.transforms.job import run_job_using
 from taskgraph.transforms.job.common import (
     docker_worker_add_tc_vcs_cache,
     docker_worker_add_gecko_vcs_env_vars,
     docker_worker_add_public_artifacts,
     docker_worker_add_tooltool,
     support_vcs_checkout,
@@ -34,32 +34,21 @@ toolchain_run_schema = Schema({
 
     # If not false, tooltool downloads will be enabled via relengAPIProxy
     # for either just public files, or all files.  Not supported on Windows
     Required('tooltool-downloads', default=False): Any(
         False,
         'public',
         'internal',
     ),
-
-    # Paths/patterns pointing to files that influence the outcome of a
-    # toolchain build.
-    Optional('resources'): [basestring],
-
-    # Path to the artifact produced by the toolchain job
-    Required('toolchain-artifact'): basestring,
-
-    # An alias that can be used instead of the real toolchain job name in
-    # the toolchains list for build jobs.
-    Optional('toolchain-alias'): basestring,
 })
 
 
 def add_optimizations(config, run, taskdesc):
-    files = list(run.get('resources', []))
+    files = []  # fixed in later commits..
     # This file
     files.append('taskcluster/taskgraph/transforms/job/toolchain.py')
     # The script
     files.append('taskcluster/scripts/misc/{}'.format(run['script']))
     # Tooltool manifest if any is defined:
     tooltool_manifest = taskdesc['worker']['env'].get('TOOLTOOL_MANIFEST')
     if tooltool_manifest:
         files.append(tooltool_manifest)
@@ -126,21 +115,16 @@ def docker_worker_toolchain(config, job,
         '--',
         'bash',
         '-c',
         'cd /builds/worker && '
         './workspace/build/src/taskcluster/scripts/misc/{}'.format(
             run['script'])
     ]
 
-    attributes = taskdesc.setdefault('attributes', {})
-    attributes['toolchain-artifact'] = run['toolchain-artifact']
-    if 'toolchain-alias' in run:
-        attributes['toolchain-alias'] = run['toolchain-alias']
-
     add_optimizations(config, run, taskdesc)
 
 
 @run_job_using("generic-worker", "toolchain-script", schema=toolchain_run_schema)
 def windows_toolchain(config, job, taskdesc):
     run = job['run']
     taskdesc['run-on-projects'] = ['trunk', 'try']
 
@@ -174,13 +158,12 @@ def windows_toolchain(config, job, taskd
     bash = r'c:\mozilla-build\msys\bin\bash'
     worker['command'] = [
         ' '.join(hg_command),
         # do something intelligent.
         r'{} -c ./build/src/taskcluster/scripts/misc/{}'.format(bash, run['script'])
     ]
 
     attributes = taskdesc.setdefault('attributes', {})
-    attributes['toolchain-artifact'] = run['toolchain-artifact']
     if 'toolchain-alias' in run:
         attributes['toolchain-alias'] = run['toolchain-alias']
 
     add_optimizations(config, run, taskdesc)

new file mode 100644
--- /dev/null
+++ b/taskcluster/taskgraph/transforms/toolchain.py
@@ -0,0 +1,121 @@
+# This Source Code Form is subject to the terms of the Mozilla Public
+# License, v. 2.0. If a copy of the MPL was not distributed with this
+# file, You can obtain one at http://mozilla.org/MPL/2.0/.
+from __future__ import absolute_import, print_function, unicode_literals
+
+import logging
+
+from voluptuous import Optional, Required, Any
+from taskgraph.util.schema import (
+    validate_schema,
+    Schema,
+)
+from taskgraph.transforms.base import TransformSequence
+from taskgraph.transforms.task import task_description_schema
+from taskgraph.transforms.job.toolchain import toolchain_run_schema
+
+logger = logging.getLogger(__name__)
+
+# Voluptuous uses marker objects as dictionary *keys*, but they are not
+# comparable, so we cast all of the keys back to regular strings
+task_description_schema = {str(k): v for k, v in task_description_schema.schema.iteritems()}
+
+toolchain_description_schema = Schema({
+    # Supplied by the task loader
+    Optional('name'): basestring,
+    Optional('job-from'): task_description_schema['job-from'],
+
+    # treeherder information
+    Required('tier', default=1): int,
+    Required('symbol'): basestring,
+    Required('description'): basestring,
+
+    # where to run builds of this toolchain.  (note, 'macosx-cross' runs on linux)
+    Required('run-on'): Any('linux', 'macosx-cross', 'windows'),
+
+    # tooltool manifest to use (sets $TOOLTOOL_MANIFEST when building)
+    Optional('tooltool-manifest'): basestring,
+
+    # Path to the artifact produced by the toolchain job.  This becomes a task
+    # attribute
+    Required('toolchain-artifact'): basestring,
+
+    # An alias that can be used instead of the real toolchain job name in
+    # the toolchains list for build jobs.  This becomes a task attribute
+    Optional('toolchain-alias'): basestring,
+
+    # See taskcluster/taskgraph/transforms/task.py
+    Optional('index'): task_description_schema['index'],
+
+    # See taskcluster/taskgraph/transforms/job/toolchain.py
+    Required('run'):  toolchain_run_schema,
+
+    # Toolchains on which this toolchain depends; see
+    # taskcluster/taskgraph/transform/use_toolchains.py
+    Required('toolchains', default=[]): [basestring],
+
+    # Paths/patterns pointing to files that influence the outcome of a
+    # toolchain build.
+    Optional('resources'): [basestring],
+})
+
+transforms = TransformSequence()
+
+
+@transforms.add
+def validate(config, jobs):
+    for job in jobs:
+        yield validate_schema(toolchain_description_schema, job,
+                              "In toolchain {!r}:".format(job.get('name', job.get('label'))))
+
+
+@transforms.add
+def toolchain_descr_to_job(config, toolchain_descriptions):
+    """Convert a toolchain description (in `/build/toolchains`) into a job
+    description with run.using toolchain-script.  (Handled in the job transform
+    taskcluster/taskgraph/transforms/jobs/toolchain.py)"""
+    for tcd in toolchain_descriptions:
+
+        job = {}
+
+        job['name'] = tcd['name']
+        job['job-from'] = tcd['job-from']
+        job['description'] = tcd['description']
+        job['run'] = tcd['run']
+        job['toolchains'] = tcd['toolchains']
+        if 'index' in tcd:
+            job['index'] = tcd['index']
+
+        job['treeherder'] = {
+            'kind': 'build',
+            'platform': 'toolchains/opt',
+            'tier': tcd.get('tier', 1),
+            'symbol': tcd['symbol'],
+        }
+
+        run_on = tcd['run-on']
+        if run_on == 'linux':
+            job['worker-type'] = 'aws-provisioner-v1/gecko-{level}-b-linux'
+            job['worker'] = {
+                'docker-image': {'in-tree': 'desktop-build'},
+                'max-run-time': 36000,
+            }
+        elif run_on == 'macosx-cross':
+            job['worker-type'] = 'aws-provisioner-v1/gecko-{level}-b-macosx64'
+            job['worker'] = {
+                'docker-image': {'in-tree': 'desktop-build'},
+                'max-run-time': 36000,
+            }
+        elif run_on == 'windows':
+            job['worker-type'] = 'aws-provisioner-v1/gecko-{level}-b-win2012'
+            job['worker'] = {'max-run-time': 36000}
+
+        tooltool_manifest = tcd.pop('tooltool-manifest', None)
+        if tooltool_manifest:
+            job['worker']['env'] = {'TOOLTOOL_MANIFEST': tooltool_manifest}
+
+        job['attributes'] = {'toolchain-artifact': tcd['toolchain-artifact']}
+        if 'toolchain-alias' in tcd:
+            job['attributes']['toolchain-alias'] = tcd['toolchain-alias']
+
+        yield job

--- a/taskcluster/taskgraph/transforms/use_toolchains.py
+++ b/taskcluster/taskgraph/transforms/use_toolchains.py
@@ -26,19 +26,18 @@ def use_toolchains(config, jobs):
             dict[key] = value
 
     # Toolchain jobs can depend on other toolchain jobs, but we don't have full
     # tasks for them, since they're being transformed. So scan the jobs list in
     # that case, otherwise, use the list of tasks for the kind dependencies.
     if config.kind == 'toolchain':
         jobs = list(jobs)
         for job in jobs:
-            run = job.get('run', {})
-            get_attribute(artifacts, job['name'], run, 'toolchain-artifact')
-            get_attribute(aliases_by_job, job['name'], run, 'toolchain-alias')
+            get_attribute(artifacts, job['name'], job['attributes'], 'toolchain-artifact')
+            get_attribute(aliases_by_job, job['name'], job['attributes'], 'toolchain-alias')
     else:
         for task in config.kind_dependencies_tasks:
             if task.kind != 'toolchain':
                 continue
             name = task.label.replace('%s-' % task.kind, '')
             get_attribute(artifacts, name, task.attributes, 'toolchain-artifact')
             get_attribute(aliases_by_job, name, task.attributes, 'toolchain-alias')