diff --git a/Cargo.lock b/Cargo.lock
index 4dfe1733c..6ae2ccbcd 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -219,6 +219,15 @@ name = "camino"
 version = "1.0.2"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "cd065703998b183ed0b348a22555691373a9345a1431141e5778b48bb17e4703"
+dependencies = [
+ "serde",
+]
+
+[[package]]
+name = "cargo_gn"
+version = "0.0.15"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "5ba7d7f7b201dfcbc314b14f2176c92f8ba521dab538b40e426ffed25ed7cd80"
 
 [[package]]
 name = "cc"
@@ -391,6 +400,26 @@ dependencies = [
  "memchr",
 ]
 
+[[package]]
+name = "deno_core"
+version = "0.73.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "f23ebf4fa4aeff8925615f339d885a73b684c274e12d329b60bb88009c2a3ab2"
+dependencies = [
+ "anyhow",
+ "futures",
+ "indexmap",
+ "lazy_static",
+ "libc",
+ "log",
+ "pin-project",
+ "rusty_v8",
+ "serde",
+ "serde_json",
+ "smallvec",
+ "url",
+]
+
 [[package]]
 name = "difference"
 version = "2.0.0"
@@ -444,6 +473,12 @@ version = "0.3.3"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "fea41bba32d969b513997752735605054bc0dfa92b4c56bf1189f2e174be7a10"
 
+[[package]]
+name = "dtoa"
+version = "0.4.7"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "88d7ed2934d741c6b37e33e3832298e8850b53fd2d2bea03873375596c7cea4e"
+
 [[package]]
 name = "either"
 version = "1.6.1"
@@ -543,6 +578,21 @@ version = "0.1.3"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "c1fd087255f739f4f1aeea69f11b72f8080e9c2e7645cd06955dad4a178a49e3"
 
+[[package]]
+name = "futures"
+version = "0.3.13"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "7f55667319111d593ba876406af7c409c0ebb44dc4be6132a783ccf163ea14c1"
+dependencies = [
+ "futures-channel",
+ "futures-core",
+ "futures-executor",
+ "futures-io",
+ "futures-sink",
+ "futures-task",
+ "futures-util",
+]
+
 [[package]]
 name = "futures-channel"
 version = "0.3.13"
@@ -550,6 +600,7 @@ source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "8c2dd2df839b57db9ab69c2c9d8f3e8c81984781937fe2807dc6dcf3b2ad2939"
 dependencies = [
  "futures-core",
+ "futures-sink",
 ]
 
 [[package]]
@@ -558,12 +609,35 @@ version = "0.3.13"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "15496a72fabf0e62bdc3df11a59a3787429221dd0710ba8ef163d6f7a9112c94"
 
+[[package]]
+name = "futures-executor"
+version = "0.3.13"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "891a4b7b96d84d5940084b2a37632dd65deeae662c114ceaa2c879629c9c0ad1"
+dependencies = [
+ "futures-core",
+ "futures-task",
+ "futures-util",
+]
+
 [[package]]
 name = "futures-io"
 version = "0.3.13"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "d71c2c65c57704c32f5241c1223167c2c3294fd34ac020c807ddbe6db287ba59"
 
+[[package]]
+name = "futures-macro"
+version = "0.3.13"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "ea405816a5139fb39af82c2beb921d52143f556038378d6db21183a5c37fbfb7"
+dependencies = [
+ "proc-macro-hack",
+ "proc-macro2",
+ "quote",
+ "syn",
+]
+
 [[package]]
 name = "futures-sink"
 version = "0.3.13"
@@ -582,12 +656,17 @@ version = "0.3.13"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "1812c7ab8aedf8d6f2701a43e1243acdbcc2b36ab26e2ad421eb99ac963d96d1"
 dependencies = [
+ "futures-channel",
  "futures-core",
  "futures-io",
+ "futures-macro",
+ "futures-sink",
  "futures-task",
  "memchr",
  "pin-project-lite",
  "pin-utils",
+ "proc-macro-hack",
+ "proc-macro-nested",
  "slab",
 ]
 
@@ -762,6 +841,19 @@ dependencies = [
  "tracing",
 ]
 
+[[package]]
+name = "harmonizer"
+version = "0.1.2"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "d7ae098cb63d7cb70d41de858363be2d31d9d817081f5f7d40526620bb8091ad"
+dependencies = [
+ "anyhow",
+ "deno_core",
+ "serde",
+ "serde_json",
+ "thiserror",
+]
+
 [[package]]
 name = "hashbrown"
 version = "0.9.1"
@@ -1006,6 +1098,12 @@ dependencies = [
  "vcpkg",
 ]
 
+[[package]]
+name = "linked-hash-map"
+version = "0.5.4"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "7fb9b38af92608140b86b693604b9ffcc5824240a484d1ecd4795bacb2fe88f3"
+
 [[package]]
 name = "lock_api"
 version = "0.4.2"
@@ -1396,6 +1494,18 @@ dependencies = [
  "version_check",
 ]
 
+[[package]]
+name = "proc-macro-hack"
+version = "0.5.19"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "dbf0c48bc1d91375ae5c3cd81e3722dff1abcf81a30960240640d223f59fe0e5"
+
+[[package]]
+name = "proc-macro-nested"
+version = "0.1.7"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "bc881b2c22681370c6a780e47af9840ef841837bc98118431d4e1868bd0c1086"
+
 [[package]]
 name = "proc-macro2"
 version = "1.0.24"
@@ -1592,6 +1702,7 @@ dependencies = [
  "console 0.14.0",
  "git-url-parse",
  "git2",
+ "harmonizer",
  "heck",
  "houston",
  "humantime",
@@ -1607,6 +1718,7 @@ dependencies = [
  "semver",
  "serde",
  "serde_json",
+ "serde_yaml",
  "serial_test",
  "sputnik",
  "strsim 0.10.0",
@@ -1662,6 +1774,19 @@ version = "1.0.4"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "cb5d2a036dc6d2d8fd16fde3498b04306e29bd193bf306a57427019b823d5acd"
 
+[[package]]
+name = "rusty_v8"
+version = "0.14.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "6bdaa4aeeae3253c3b34486af66527d9982105d79ba57cf9b50b217e7b47a8b6"
+dependencies = [
+ "bitflags",
+ "cargo_gn",
+ "lazy_static",
+ "libc",
+ "which",
+]
+
 [[package]]
 name = "ryu"
 version = "1.0.5"
@@ -1761,6 +1886,7 @@ version = "1.0.64"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "799e97dc9fdae36a5c8b8f2cae9ce2ee9fdce2058c57a93e6099d919fd982f79"
 dependencies = [
+ "indexmap",
  "itoa",
  "ryu",
  "serde",
@@ -1778,6 +1904,18 @@ dependencies = [
  "serde",
 ]
 
+[[package]]
+name = "serde_yaml"
+version = "0.8.17"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "15654ed4ab61726bf918a39cb8d98a2e2995b002387807fa6ba58fdf7f59bb23"
+dependencies = [
+ "dtoa",
+ "linked-hash-map",
+ "serde",
+ "yaml-rust",
+]
+
 [[package]]
 name = "serial_test"
 version = "0.5.1"
@@ -2292,6 +2430,7 @@ dependencies = [
  "idna",
  "matches",
  "percent-encoding",
+ "serde",
 ]
 
 [[package]]
@@ -2506,3 +2645,12 @@ checksum = "d107f8c6e916235c4c01cabb3e8acf7bea8ef6a63ca2e7fa0527c049badfc48c"
 dependencies = [
  "winapi",
 ]
+
+[[package]]
+name = "yaml-rust"
+version = "0.4.5"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "56c1936c4cc7a1c9ab21a1ebb602eb942ba868cbd44a99cb7cdc5892335e1c85"
+dependencies = [
+ "linked-hash-map",
+]
diff --git a/Cargo.toml b/Cargo.toml
index b382350e5..55879feaf 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -35,12 +35,13 @@ timber = { path = "./crates/timber" }
 anyhow = "1.0.38"
 atty = "0.2.14"
 ansi_term = "0.12.1"
-camino = "1.0.2"
+camino = { version = "1.0.2", features = ["serde1"] }
 billboard = { git = "https://github.com/EverlastingBugstopper/billboard.git", branch = "main" }
 chrono = "0.4"
 console = "0.14.0"
 git2 = "0.13.17"
 git-url-parse = "0.3.1"
+harmonizer = "0.1.2"
 heck = "0.3.2"
 humantime = "2.1.0"
 opener = "0.4.1"
@@ -51,10 +52,11 @@ strsim = "0.10"
 serde_json = "1.0"
 structopt = "0.3.21"
 tracing = "0.1.22"
+toml = "0.5"
 regex = "1"
 url = "2.2.0"
 semver = "0.11"
-toml = "0.5"
+serde_yaml = "0.8"
 
 [dev-dependencies]
 assert_cmd = "1.0.1"
diff --git a/installers/npm/package-lock.json b/installers/npm/package-lock.json
index 3eded8c7b..811fcad41 100644
--- a/installers/npm/package-lock.json
+++ b/installers/npm/package-lock.json
@@ -1,301 +1,8 @@
 {
   "name": "@apollo/rover",
   "version": "0.0.3",
-  "lockfileVersion": 2,
+  "lockfileVersion": 1,
   "requires": true,
-  "packages": {
-    "": {
-      "name": "@apollo/rover",
-      "version": "0.0.3",
-      "hasInstallScript": true,
-      "license": "MIT",
-      "dependencies": {
-        "binary-install": "^0.1.1",
-        "console.table": "^0.10.0"
-      },
-      "bin": {
-        "rover": "run.js"
-      },
-      "devDependencies": {
-        "prettier": "^2.2.1"
-      }
-    },
-    "node_modules/axios": {
-      "version": "0.21.1",
-      "resolved": "https://registry.npmjs.org/axios/-/axios-0.21.1.tgz",
-      "integrity": "sha512-dKQiRHxGD9PPRIUNIWvZhPTPpl1rf/OxTYKsqKUDjBwYylTvV7SjSHJb9ratfyzM6wCdLCOYLzs73qpg5c4iGA==",
-      "dependencies": {
-        "follow-redirects": "^1.10.0"
-      }
-    },
-    "node_modules/balanced-match": {
-      "version": "1.0.0",
-      "resolved": "https://registry.npmjs.org/balanced-match/-/balanced-match-1.0.0.tgz",
-      "integrity": "sha1-ibTRmasr7kneFk6gK4nORi1xt2c="
-    },
-    "node_modules/binary-install": {
-      "version": "0.1.1",
-      "resolved": "https://registry.npmjs.org/binary-install/-/binary-install-0.1.1.tgz",
-      "integrity": "sha512-DqED0D/6LrS+BHDkKn34vhRqOGjy5gTMgvYZsGK2TpNbdPuz4h+MRlNgGv5QBRd7pWq/jylM4eKNCizgAq3kNQ==",
-      "dependencies": {
-        "axios": "^0.21.1",
-        "rimraf": "^3.0.2",
-        "tar": "^6.1.0"
-      },
-      "engines": {
-        "node": ">=10"
-      }
-    },
-    "node_modules/brace-expansion": {
-      "version": "1.1.11",
-      "resolved": "https://registry.npmjs.org/brace-expansion/-/brace-expansion-1.1.11.tgz",
-      "integrity": "sha512-iCuPHDFgrHX7H2vEI/5xpz07zSHB00TpugqhmYtVmMO6518mCuRMoOYFldEBl0g187ufozdaHgWKcYFb61qGiA==",
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-        "concat-map": "0.0.1"
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-        }
-      ],
-      "engines": {
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-      }
-    },
-    "node_modules/rimraf": {
-      "version": "3.0.2",
-      "resolved": "https://registry.npmjs.org/rimraf/-/rimraf-3.0.2.tgz",
-      "integrity": "sha512-JZkJMZkAGFFPP2YqXZXPbMlMBgsxzE8ILs4lMIX/2o0L9UBw9O/Y3o6wFw/i9YLapcUJWwqbi3kdxIPdC62TIA==",
-      "dependencies": {
-        "glob": "^7.1.3"
-      },
-      "bin": {
-        "rimraf": "bin.js"
-      },
-      "funding": {
-        "url": "https://github.com/sponsors/isaacs"
-      }
-    },
-    "node_modules/tar": {
-      "version": "6.1.0",
-      "resolved": "https://registry.npmjs.org/tar/-/tar-6.1.0.tgz",
-      "integrity": "sha512-DUCttfhsnLCjwoDoFcI+B2iJgYa93vBnDUATYEeRx6sntCTdN01VnqsIuTlALXla/LWooNg0yEGeB+Y8WdFxGA==",
-      "dependencies": {
-        "chownr": "^2.0.0",
-        "fs-minipass": "^2.0.0",
-        "minipass": "^3.0.0",
-        "minizlib": "^2.1.1",
-        "mkdirp": "^1.0.3",
-        "yallist": "^4.0.0"
-      },
-      "engines": {
-        "node": ">= 10"
-      }
-    },
-    "node_modules/wcwidth": {
-      "version": "1.0.1",
-      "resolved": "https://registry.npmjs.org/wcwidth/-/wcwidth-1.0.1.tgz",
-      "integrity": "sha1-8LDc+RW8X/FSivrbLA4XtTLaL+g=",
-      "optional": true,
-      "dependencies": {
-        "defaults": "^1.0.3"
-      }
-    },
-    "node_modules/wrappy": {
-      "version": "1.0.2",
-      "resolved": "https://registry.npmjs.org/wrappy/-/wrappy-1.0.2.tgz",
-      "integrity": "sha1-tSQ9jz7BqjXxNkYFvA0QNuMKtp8="
-    },
-    "node_modules/yallist": {
-      "version": "4.0.0",
-      "resolved": "https://registry.npmjs.org/yallist/-/yallist-4.0.0.tgz",
-      "integrity": "sha512-3wdGidZyq5PB084XLES5TpOSRA3wjXAlIWMhum2kRcv/41Sn2emQ0dycQW4uZXLejwKvg6EsvbdlVL+FYEct7A=="
-    }
-  },
   "dependencies": {
     "axios": {
       "version": "0.21.1",
diff --git a/src/cli.rs b/src/cli.rs
index eadc0291c..77024dd48 100644
--- a/src/cli.rs
+++ b/src/cli.rs
@@ -90,6 +90,9 @@ pub enum Command {
     /// Configuration profile commands
     Config(command::Config),
 
+    /// Core schema commands
+    Core(command::Core),
+
     /// Non-federated schema/graph commands
     Graph(command::Graph),
 
@@ -126,6 +129,7 @@ impl Rover {
             Command::Config(command) => {
                 command.run(self.get_rover_config()?, self.get_client_config()?)
             }
+            Command::Core(command) => command.run(),
             Command::Docs(command) => command.run(),
             Command::Graph(command) => {
                 command.run(self.get_client_config()?, self.get_git_context()?)
diff --git a/src/command/core/build.rs b/src/command/core/build.rs
new file mode 100644
index 000000000..52bf1d338
--- /dev/null
+++ b/src/command/core/build.rs
@@ -0,0 +1,45 @@
+use crate::{anyhow, command::RoverStdout, Result};
+
+use ansi_term::Colour::Red;
+use camino::Utf8PathBuf;
+use serde::Serialize;
+use structopt::StructOpt;
+
+use super::config;
+
+#[derive(Debug, Serialize, StructOpt)]
+pub struct Build {
+    /// The relative path to the core configuration file.
+    #[structopt(long = "config")]
+    #[serde(skip_serializing)]
+    config_path: Utf8PathBuf,
+}
+
+impl Build {
+    pub fn run(&self) -> Result<RoverStdout> {
+        let core_config = config::parse_core_config(&self.config_path)?;
+        let subgraph_definitions = core_config.get_subgraph_definitions(&self.config_path)?;
+
+        match harmonizer::harmonize(subgraph_definitions) {
+            Ok(csdl) => Ok(RoverStdout::CSDL(csdl)),
+            Err(composition_errors) => {
+                let num_failures = composition_errors.len();
+                for composition_error in composition_errors {
+                    eprintln!("{} {}", Red.bold().paint("error:"), &composition_error)
+                }
+                match num_failures {
+                    0 => unreachable!("Composition somehow failed with no composition errors."),
+                    1 => Err(
+                        anyhow!("Encountered 1 composition error while composing the graph.")
+                            .into(),
+                    ),
+                    _ => Err(anyhow!(
+                        "Encountered {} composition errors while composing the graph.",
+                        num_failures
+                    )
+                    .into()),
+                }
+            }
+        }
+    }
+}
diff --git a/src/command/core/config.rs b/src/command/core/config.rs
new file mode 100644
index 000000000..e6224a932
--- /dev/null
+++ b/src/command/core/config.rs
@@ -0,0 +1,192 @@
+use crate::{anyhow, Result};
+
+use camino::Utf8PathBuf;
+use harmonizer::ServiceDefinition as SubgraphDefinition;
+use serde::{Deserialize, Serialize};
+
+use std::collections::HashMap;
+use std::fs;
+
+#[derive(Debug, Clone, Serialize, Deserialize)]
+pub(crate) struct CoreConfig {
+    pub(crate) subgraphs: HashMap<String, Subgraph>,
+}
+
+#[derive(Debug, Clone, Serialize, Deserialize)]
+pub(crate) struct Subgraph {
+    pub(crate) routing_url: String,
+    pub(crate) schema: Schema,
+}
+
+#[derive(Debug, Clone, Serialize, Deserialize)]
+pub(crate) struct Schema {
+    pub(crate) file: Utf8PathBuf,
+}
+
+pub(crate) fn parse_core_config(config_path: &Utf8PathBuf) -> Result<CoreConfig> {
+    let raw_core_config = fs::read_to_string(config_path)
+        .map_err(|e| anyhow!("Could not read \"{}\": {}", config_path, e))?;
+
+    let parsed_config = serde_yaml::from_str(&raw_core_config)
+        .map_err(|e| anyhow!("Could not parse YAML from \"{}\": {}", config_path, e))?;
+
+    tracing::debug!(?parsed_config);
+
+    Ok(parsed_config)
+}
+
+impl CoreConfig {
+    pub(crate) fn get_subgraph_definitions(
+        &self,
+        config_path: &Utf8PathBuf,
+    ) -> Result<Vec<SubgraphDefinition>> {
+        let mut subgraphs = Vec::new();
+
+        for (subgraph_name, subgraph_data) in &self.subgraphs {
+            // compute the path to the schema relative to the config file itself, not the working directory.
+            let relative_schema_path = if let Some(parent) = config_path.parent() {
+                let mut schema_path = parent.to_path_buf();
+                schema_path.push(&subgraph_data.schema.file);
+                schema_path
+            } else {
+                subgraph_data.schema.file.clone()
+            };
+
+            let schema = fs::read_to_string(&relative_schema_path)
+                .map_err(|e| anyhow!("Could not read \"{}\": {}", &relative_schema_path, e))?;
+
+            let subgraph_definition =
+                SubgraphDefinition::new(subgraph_name, &subgraph_data.routing_url, &schema);
+
+            subgraphs.push(subgraph_definition);
+        }
+
+        Ok(subgraphs)
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use assert_fs::TempDir;
+    use camino::Utf8PathBuf;
+    use std::fs;
+
+    #[test]
+    fn it_can_parse_valid_config() {
+        let raw_good_yaml = r#"subgraphs:
+  films:
+    routing_url: https://films.example.com
+    schema: 
+      file: ./good-films.graphql
+  people:
+    routing_url: https://people.example.com
+    schema: 
+      file: ./good-people.graphql
+"#;
+        let tmp_home = TempDir::new().unwrap();
+        let mut config_path = Utf8PathBuf::from_path_buf(tmp_home.path().to_path_buf()).unwrap();
+        config_path.push("config.yaml");
+        fs::write(&config_path, raw_good_yaml).unwrap();
+
+        let core_config = super::parse_core_config(&config_path);
+        if let Err(e) = core_config {
+            panic!(e.to_string())
+        }
+    }
+
+    #[test]
+    fn it_errors_on_invalid_config() {
+        let raw_bad_yaml = r#"subgraphs:
+  films:
+    routing_______url: https://films.example.com
+    schemaaaa: 
+        file:: ./good-films.graphql
+  people:
+    routing____url: https://people.example.com
+    schema_____file: ./good-people.graphql"#;
+        let tmp_home = TempDir::new().unwrap();
+        let mut config_path = Utf8PathBuf::from_path_buf(tmp_home.path().to_path_buf()).unwrap();
+        config_path.push("config.yaml");
+        fs::write(&config_path, raw_bad_yaml).unwrap();
+        assert!(super::parse_core_config(&config_path).is_err())
+    }
+
+    #[test]
+    fn it_errs_on_invalid_subgraph_path() {
+        let raw_good_yaml = r#"subgraphs:
+  films:
+    routing_url: https://films.example.com
+    schema: 
+      file: ./films-do-not-exist.graphql
+  people:
+    routing_url: https://people.example.com
+    schema: 
+      file: ./people-do-not-exist.graphql"#;
+        let tmp_home = TempDir::new().unwrap();
+        let mut config_path = Utf8PathBuf::from_path_buf(tmp_home.path().to_path_buf()).unwrap();
+        config_path.push("config.yaml");
+        fs::write(&config_path, raw_good_yaml).unwrap();
+        let core_config = super::parse_core_config(&config_path).unwrap();
+        assert!(core_config.get_subgraph_definitions(&config_path).is_err())
+    }
+
+    #[test]
+    fn it_can_get_subgraph_definitions_from_fs() {
+        let raw_good_yaml = r#"subgraphs:
+  films:
+    routing_url: https://films.example.com
+    schema: 
+      file: ./films.graphql
+  people:
+    routing_url: https://people.example.com
+    schema: 
+      file: ./people.graphql"#;
+        let tmp_home = TempDir::new().unwrap();
+        let mut config_path = Utf8PathBuf::from_path_buf(tmp_home.path().to_path_buf()).unwrap();
+        config_path.push("config.yaml");
+        fs::write(&config_path, raw_good_yaml).unwrap();
+        let tmp_dir = config_path.parent().unwrap().to_path_buf();
+        let films_path = tmp_dir.join("films.graphql");
+        let people_path = tmp_dir.join("people.graphql");
+        fs::write(films_path, "there is something here").unwrap();
+        fs::write(people_path, "there is also something here").unwrap();
+        let core_config = super::parse_core_config(&config_path).unwrap();
+        assert!(core_config.get_subgraph_definitions(&config_path).is_ok())
+    }
+
+    #[test]
+    fn it_can_compute_relative_schema_paths() {
+        let raw_good_yaml = r#"subgraphs:
+  films:
+    routing_url: https://films.example.com
+    schema: 
+      file: ../../films.graphql
+  people:
+    routing_url: https://people.example.com
+    schema: 
+        file: ../../people.graphql"#;
+        let tmp_home = TempDir::new().unwrap();
+        let tmp_dir = Utf8PathBuf::from_path_buf(tmp_home.path().to_path_buf()).unwrap();
+        let mut config_path = tmp_dir.clone();
+        config_path.push("layer");
+        config_path.push("layer");
+        fs::create_dir_all(&config_path).unwrap();
+        config_path.push("config.yaml");
+        fs::write(&config_path, raw_good_yaml).unwrap();
+        let films_path = tmp_dir.join("films.graphql");
+        let people_path = tmp_dir.join("people.graphql");
+        fs::write(films_path, "there is something here").unwrap();
+        fs::write(people_path, "there is also something here").unwrap();
+        let core_config = super::parse_core_config(&config_path).unwrap();
+        let subgraph_definitions = core_config.get_subgraph_definitions(&config_path).unwrap();
+        let people_subgraph = subgraph_definitions.get(0).unwrap();
+        let film_subgraph = subgraph_definitions.get(1).unwrap();
+
+        assert_eq!(film_subgraph.name, "films");
+        assert_eq!(film_subgraph.url, "https://films.example.com");
+        assert_eq!(film_subgraph.type_defs, "there is something here");
+        assert_eq!(people_subgraph.name, "people");
+        assert_eq!(people_subgraph.url, "https://people.example.com");
+        assert_eq!(people_subgraph.type_defs, "there is also something here");
+    }
+}
diff --git a/src/command/core/mod.rs b/src/command/core/mod.rs
new file mode 100644
index 000000000..eec91ce7f
--- /dev/null
+++ b/src/command/core/mod.rs
@@ -0,0 +1,28 @@
+mod build;
+pub(crate) mod config;
+
+use serde::Serialize;
+use structopt::StructOpt;
+
+use crate::command::RoverStdout;
+use crate::Result;
+
+#[derive(Debug, Serialize, StructOpt)]
+pub struct Core {
+    #[structopt(subcommand)]
+    command: Command,
+}
+
+#[derive(Debug, Serialize, StructOpt)]
+pub enum Command {
+    /// Build a core schema from a set of subgraphs.
+    Build(build::Build),
+}
+
+impl Core {
+    pub fn run(&self) -> Result<RoverStdout> {
+        match &self.command {
+            Command::Build(command) => command.run(),
+        }
+    }
+}
diff --git a/src/command/graph/mod.rs b/src/command/graph/mod.rs
index 9c80664fa..a655ea68a 100644
--- a/src/command/graph/mod.rs
+++ b/src/command/graph/mod.rs
@@ -35,9 +35,9 @@ impl Graph {
         git_context: GitContext,
     ) -> Result<RoverStdout> {
         match &self.command {
+            Command::Check(command) => command.run(client_config, git_context),
             Command::Fetch(command) => command.run(client_config),
             Command::Publish(command) => command.run(client_config, git_context),
-            Command::Check(command) => command.run(client_config, git_context),
         }
     }
 }
diff --git a/src/command/mod.rs b/src/command/mod.rs
index 7bbe9440f..38bef50b5 100644
--- a/src/command/mod.rs
+++ b/src/command/mod.rs
@@ -1,4 +1,5 @@
 mod config;
+mod core;
 mod docs;
 mod graph;
 mod info;
@@ -7,6 +8,7 @@ mod output;
 mod subgraph;
 mod update;
 
+pub use self::core::Core;
 pub use config::Config;
 pub use docs::Docs;
 pub use graph::Graph;
diff --git a/src/command/output.rs b/src/command/output.rs
index ae289b66e..4eb673853 100644
--- a/src/command/output.rs
+++ b/src/command/output.rs
@@ -18,6 +18,7 @@ use crate::utils::table::{self, cell, row};
 pub enum RoverStdout {
     DocsList(HashMap<&'static str, &'static str>),
     SDL(String),
+    CSDL(String),
     SchemaHash(String),
     SubgraphList(ListDetails),
     VariantList(Vec<String>),
@@ -46,6 +47,10 @@ impl RoverStdout {
                 eprintln!("SDL:");
                 println!("{}", &sdl);
             }
+            RoverStdout::CSDL(csdl) => {
+                eprintln!("CSDL:");
+                println!("{}", &csdl);
+            }
             RoverStdout::SchemaHash(hash) => {
                 eprint!("Schema Hash: ");
                 println!("{}", &hash);
diff --git a/src/command/subgraph/check.rs b/src/command/subgraph/check.rs
index 22755c587..eda0ed251 100644
--- a/src/command/subgraph/check.rs
+++ b/src/command/subgraph/check.rs
@@ -157,9 +157,8 @@ fn handle_checks(check_result: check::CheckResult) -> Result<RoverStdout> {
 fn handle_composition_errors(
     composition_errors: &[check::check_partial_schema_query::CheckPartialSchemaQueryServiceCheckPartialSchemaCompositionValidationResultErrors],
 ) -> Result<RoverStdout> {
-    let mut num_failures = 0;
+    let num_failures = composition_errors.len();
     for error in composition_errors {
-        num_failures += 1;
         eprintln!("{} {}", Red.bold().paint("error:"), &error.message);
     }
     match num_failures {