diff --git a/Cargo.lock b/Cargo.lock
index 5109cfe..1827aca 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -528,6 +528,9 @@ name = "deranged"
 version = "0.3.7"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "7684a49fb1af197853ef7b2ee694bc1f5b4179556f1e5710e1760c5db6f5e929"
+dependencies = [
+ "serde",
+]
 
 [[package]]
 name = "digest"
@@ -2382,6 +2385,17 @@ dependencies = [
  "serde",
 ]
 
+[[package]]
+name = "serde_repr"
+version = "0.1.16"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "8725e1dfadb3a50f7e5ce0b1a540466f6ed3fe7a0fca2ac2b8b831d31316bd00"
+dependencies = [
+ "proc-macro2",
+ "quote",
+ "syn 2.0.28",
+]
+
 [[package]]
 name = "serde_spanned"
 version = "0.6.3"
@@ -2813,6 +2827,7 @@ dependencies = [
  "rand",
  "rust-embed",
  "serde",
+ "serde_repr",
  "sqlx",
  "time",
  "tokio",
diff --git a/Cargo.toml b/Cargo.toml
index 013b3a9..d427ed5 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -18,8 +18,8 @@ mime_guess = "2.0.4"
 rand = "0.8.5"
 rust-embed = { version = "6.8.1", features = ["interpolate-folder-path"] }
 serde = { version = "1.0.181", features = ["derive"] }
+serde_repr = "0.1.16"
 sqlx = { version = "0.7.1", features = ["runtime-tokio", "sqlite", "time"] }
-time = { version = "0.3.25", features = ["formatting", "macros", "parsing"] }
 tokio = { version = "1.29.1", features = ["full"] }
 toml = "0.7.6"
 tracing = "0.1.37"
@@ -30,6 +30,10 @@ version = "0.51.0"
 default-features = false
 features = ["max-performance-safe", "extras"]
 
+[dependencies.time]
+version = "0.3.25"
+features = ["formatting", "parsing", "macros", "serde-human-readable"]
+
 [build-dependencies]
 vergen = { version = "8.2.4", features = ["git", "gitcl"] }
 walkdir = "2.3.3"
diff --git a/src/main.rs b/src/main.rs
index 7fabdbe..7cf839a 100644
--- a/src/main.rs
+++ b/src/main.rs
@@ -3,6 +3,7 @@ mod config;
 mod runner;
 mod server;
 mod somehow;
+mod shared;
 
 use std::{io, process};
 
diff --git a/src/shared.rs b/src/shared.rs
new file mode 100644
index 0000000..a5112f8
--- /dev/null
+++ b/src/shared.rs
@@ -0,0 +1,129 @@
+//! Data structures modelling the communication between server and runner.
+
+use std::collections::HashMap;
+
+use serde::{Deserialize, Serialize};
+use serde_repr::{Deserialize_repr, Serialize_repr};
+use time::OffsetDateTime;
+
+#[derive(Serialize_repr, Deserialize_repr)]
+#[repr(i8)]
+pub enum Direction {
+    LessIsBetter = -1,
+    Neutral = 0,
+    MoreIsBetter = 1,
+}
+
+#[derive(Serialize, Deserialize)]
+pub struct Measurement {
+    pub value: f64,
+    pub stddev: Option<f64>,
+    pub unit: Option<String>,
+    pub direction: Option<i8>,
+}
+
+#[derive(Serialize, Deserialize)]
+#[serde(rename = "snake_case")]
+#[serde(tag = "type")]
+pub enum Line {
+    Stdout(String),
+    Stderr(String),
+}
+
+#[derive(Serialize, Deserialize)]
+pub struct FinishedRun {
+    pub id: String,
+    pub start: OffsetDateTime,
+    pub end: OffsetDateTime,
+    pub output: Vec<Line>,
+    pub exit_code: i32,
+    pub measurements: HashMap<String, Measurement>,
+}
+
+#[derive(Serialize, Deserialize)]
+#[serde(rename = "snake_case")]
+#[serde(tag = "type")]
+pub enum RunnerStatus {
+    /// The runner is not performing any work.
+    Idle,
+    /// The runner is performing work for another server.
+    Busy,
+    /// The runner is performing work for the current server.
+    Working {
+        id: String,
+        hash: String,
+        since: OffsetDateTime,
+        last_lines: Vec<Line>,
+    },
+}
+
+#[derive(Serialize, Deserialize)]
+pub struct Request {
+    /// The runner's name.
+    ///
+    /// This name is shown to the user in the UI and used to identify the runner
+    /// in URLs. Because of this, only these characters are allowed:
+    ///
+    /// - Letters from `a` to `z`, both lowercase and uppercase
+    /// - Digits from `0` to `9`
+    /// - The hyphen `-`, underscore `_`, and dot `.` characters
+    ///
+    /// Additionally, the name must be at least one character long.
+    pub name: String,
+
+    /// Additional free-form info about the runner.
+    ///
+    /// This could for example be used to describe the runner's system specs.
+    pub info: Option<String>,
+
+    /// Secret for preventing name collisions.
+    pub secret: String,
+
+    /// What the runner is currently working on.
+    pub status: RunnerStatus,
+
+    /// Whether the runner wants new work from the server.
+    ///
+    /// If the server has a commit available, it should respond with a non-null
+    /// [`Response::work`].
+    pub request_work: bool,
+
+    /// The runner has finished a run and wants to submit the results.
+    pub submit_work: Option<FinishedRun>,
+}
+
+#[derive(Serialize, Deserialize)]
+#[serde(rename = "snake_case")]
+#[serde(tag = "type")]
+pub enum BenchMethod {
+    /// Use internal (deterministic) benchmarking code.
+    Internal,
+    /// Use a commit from a bench repo.
+    BenchRepo { hash: String },
+}
+
+#[derive(Serialize, Deserialize)]
+pub struct Work {
+    /// Hash of commit to benchmark.
+    pub hash: String,
+    /// How to benchmark the commit.
+    pub bench: BenchMethod,
+}
+
+#[derive(Serialize, Deserialize)]
+pub struct Response {
+    /// Work the runner requested using [`Request::request_work].
+    ///
+    /// The runner may ignore this work and do something else. However, until
+    /// the next update request sent by the runner, the server will consider the
+    /// runner as preparing to work on the commit, and will not give out the
+    /// same commit to other runners.
+    pub work: Option<Work>,
+
+    /// The runner should abort the current run.
+    ///
+    /// The server may send this because it detected the runner is benchmarking
+    /// the same commit as another runner and has broken the tie in favor of the
+    /// other runner. The runner may continue the run despite this flag.
+    pub abort_work: bool,
+}