diff --git a/.github/workflows/date-check.yml b/.github/workflows/date-check.yml
new file mode 100644
index 00000000..41111723
--- /dev/null
+++ b/.github/workflows/date-check.yml
@@ -0,0 +1,44 @@
+name: Date-Check
+
+on:
+  schedule:
+    # Run at noon UTC every 1st of the month
+    - cron: '00 12 01 * *'
+
+  # Allow manually starting the workflow
+  workflow_dispatch:
+
+jobs:
+  date-check:
+    runs-on: ubuntu-latest
+
+    steps:
+      - name: Checkout repo
+        uses: actions/checkout@v2
+
+      - name: Run `date-check`
+        working-directory: ci/date-check
+        run: |
+          cargo run -- ../../src/ > ../../date-check-output.txt
+
+      - name: Open issue
+        uses: actions/github-script@v3
+        with:
+          github-token: ${{secrets.GITHUB_TOKEN}}
+          script: |
+            const fs = require('fs');
+
+            const rawText = fs.readFileSync('date-check-output.txt', { encoding: 'utf8' });
+            const title = rawText.split('\n')[0];
+            if (title != 'empty') {
+                const body = rawText.split('\n').slice(1).join('\n');
+                github.issues.create({
+                  owner: context.repo.owner,
+                  repo: context.repo.repo,
+                  title,
+                  body,
+                });
+                console.log('Opened issue.');
+            } else {
+                console.log('No dates to triage.');
+            }
diff --git a/.gitignore b/.gitignore
index b8cb3488..2901de5e 100644
--- a/.gitignore
+++ b/.gitignore
@@ -1,4 +1,6 @@
 book
 
-# prevent accidentally changes
+# prevent accidental changes
 book.toml
+
+ci/date-check/target/
diff --git a/ci/date-check/Cargo.lock b/ci/date-check/Cargo.lock
new file mode 100644
index 00000000..296a132d
--- /dev/null
+++ b/ci/date-check/Cargo.lock
@@ -0,0 +1,147 @@
+# This file is automatically @generated by Cargo.
+# It is not intended for manual editing.
+[[package]]
+name = "aho-corasick"
+version = "0.7.15"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "7404febffaa47dac81aa44dba71523c9d069b1bdc50a77db41195149e17f68e5"
+dependencies = [
+ "memchr",
+]
+
+[[package]]
+name = "autocfg"
+version = "1.0.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "cdb031dd78e28731d87d56cc8ffef4a8f36ca26c38fe2de700543e627f8a464a"
+
+[[package]]
+name = "chrono"
+version = "0.4.19"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "670ad68c9088c2a963aaa298cb369688cf3f9465ce5e2d4ca10e6e0098a1ce73"
+dependencies = [
+ "libc",
+ "num-integer",
+ "num-traits",
+ "time",
+ "winapi",
+]
+
+[[package]]
+name = "date-check"
+version = "0.1.0"
+dependencies = [
+ "chrono",
+ "glob",
+ "regex",
+]
+
+[[package]]
+name = "glob"
+version = "0.3.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "9b919933a397b79c37e33b77bb2aa3dc8eb6e165ad809e58ff75bc7db2e34574"
+
+[[package]]
+name = "lazy_static"
+version = "1.4.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "e2abad23fbc42b3700f2f279844dc832adb2b2eb069b2df918f455c4e18cc646"
+
+[[package]]
+name = "libc"
+version = "0.2.82"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "89203f3fba0a3795506acaad8ebce3c80c0af93f994d5a1d7a0b1eeb23271929"
+
+[[package]]
+name = "memchr"
+version = "2.3.4"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "0ee1c47aaa256ecabcaea351eae4a9b01ef39ed810004e298d2511ed284b1525"
+
+[[package]]
+name = "num-integer"
+version = "0.1.44"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "d2cc698a63b549a70bc047073d2949cce27cd1c7b0a4a862d08a8031bc2801db"
+dependencies = [
+ "autocfg",
+ "num-traits",
+]
+
+[[package]]
+name = "num-traits"
+version = "0.2.14"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "9a64b1ec5cda2586e284722486d802acf1f7dbdc623e2bfc57e65ca1cd099290"
+dependencies = [
+ "autocfg",
+]
+
+[[package]]
+name = "regex"
+version = "1.4.3"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "d9251239e129e16308e70d853559389de218ac275b515068abc96829d05b948a"
+dependencies = [
+ "aho-corasick",
+ "memchr",
+ "regex-syntax",
+ "thread_local",
+]
+
+[[package]]
+name = "regex-syntax"
+version = "0.6.22"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "b5eb417147ba9860a96cfe72a0b93bf88fee1744b5636ec99ab20c1aa9376581"
+
+[[package]]
+name = "thread_local"
+version = "1.1.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "bb9bc092d0d51e76b2b19d9d85534ffc9ec2db959a2523cdae0697e2972cd447"
+dependencies = [
+ "lazy_static",
+]
+
+[[package]]
+name = "time"
+version = "0.1.44"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "6db9e6914ab8b1ae1c260a4ae7a49b6c5611b40328a735b21862567685e73255"
+dependencies = [
+ "libc",
+ "wasi",
+ "winapi",
+]
+
+[[package]]
+name = "wasi"
+version = "0.10.0+wasi-snapshot-preview1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "1a143597ca7c7793eff794def352d41792a93c481eb1042423ff7ff72ba2c31f"
+
+[[package]]
+name = "winapi"
+version = "0.3.9"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "5c839a674fcd7a98952e593242ea400abe93992746761e38641405d28b00f419"
+dependencies = [
+ "winapi-i686-pc-windows-gnu",
+ "winapi-x86_64-pc-windows-gnu",
+]
+
+[[package]]
+name = "winapi-i686-pc-windows-gnu"
+version = "0.4.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "ac3b87c63620426dd9b991e5ce0329eff545bccbbb34f3be09ff6fb6ab51b7b6"
+
+[[package]]
+name = "winapi-x86_64-pc-windows-gnu"
+version = "0.4.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "712e227841d057c1ee1cd2fb22fa7e5a5461ae8e48fa2ca79ec42cfc1931183f"
diff --git a/ci/date-check/Cargo.toml b/ci/date-check/Cargo.toml
new file mode 100644
index 00000000..95251fb1
--- /dev/null
+++ b/ci/date-check/Cargo.toml
@@ -0,0 +1,12 @@
+[package]
+name = "date-check"
+version = "0.1.0"
+authors = ["Camelid <camelidcamel@gmail.com>"]
+edition = "2018"
+
+# See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html
+
+[dependencies]
+glob = "0.3"
+regex = "1"
+chrono = "0.4"
diff --git a/ci/date-check/src/main.rs b/ci/date-check/src/main.rs
new file mode 100644
index 00000000..d78b430b
--- /dev/null
+++ b/ci/date-check/src/main.rs
@@ -0,0 +1,236 @@
+use std::{
+    collections::BTreeMap,
+    convert::TryInto as _,
+    env, fmt, fs,
+    path::{Path, PathBuf},
+};
+
+use chrono::{Datelike as _, TimeZone as _, Utc};
+use glob::glob;
+use regex::Regex;
+
+#[derive(Debug, Copy, Clone, PartialEq, Eq)]
+struct Date {
+    year: u32,
+    month: u32,
+}
+
+impl Date {
+    fn months_since(self, other: Date) -> Option<u32> {
+        let self_chrono = Utc.ymd(self.year.try_into().unwrap(), self.month, 1);
+        let other_chrono = Utc.ymd(other.year.try_into().unwrap(), other.month, 1);
+        let duration_since = self_chrono.signed_duration_since(other_chrono);
+        let months_since = duration_since.num_days() / 30;
+        if months_since < 0 {
+            None
+        } else {
+            Some(months_since.try_into().unwrap())
+        }
+    }
+}
+
+impl fmt::Display for Date {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        write!(f, "{:04}-{:02}", self.year, self.month)
+    }
+}
+
+fn make_date_regex() -> Regex {
+    Regex::new(
+        r"(?x) # insignificant whitespace mode
+        <!--\s*
+        date:\s*
+        (?P<y>\d{4}) # year
+        -
+        (?P<m>\d{2}) # month
+        \s*-->",
+    )
+    .unwrap()
+}
+
+fn collect_dates_from_file(date_regex: &Regex, text: &str) -> Vec<(usize, Date)> {
+    let mut line = 1;
+    let mut end_of_last_cap = 0;
+    date_regex
+        .captures_iter(&text)
+        .map(|cap| {
+            (
+                cap.get(0).unwrap().range(),
+                Date {
+                    year: cap["y"].parse().unwrap(),
+                    month: cap["m"].parse().unwrap(),
+                },
+            )
+        })
+        .map(|(byte_range, date)| {
+            line += text[end_of_last_cap..byte_range.end]
+                .chars()
+                .filter(|c| *c == '\n')
+                .count();
+            end_of_last_cap = byte_range.end;
+            (line, date)
+        })
+        .collect()
+}
+
+fn collect_dates(paths: impl Iterator<Item = PathBuf>) -> BTreeMap<PathBuf, Vec<(usize, Date)>> {
+    let date_regex = make_date_regex();
+    let mut data = BTreeMap::new();
+    for path in paths {
+        let text = fs::read_to_string(&path).unwrap();
+        let dates = collect_dates_from_file(&date_regex, &text);
+        if !dates.is_empty() {
+            data.insert(path, dates);
+        }
+    }
+    data
+}
+
+fn filter_dates(
+    current_month: Date,
+    min_months_since: u32,
+    dates_by_file: impl Iterator<Item = (PathBuf, Vec<(usize, Date)>)>,
+) -> impl Iterator<Item = (PathBuf, Vec<(usize, Date)>)> {
+    dates_by_file
+        .map(move |(path, dates)| {
+            (
+                path,
+                dates
+                    .into_iter()
+                    .filter(|(_, date)| {
+                        current_month
+                            .months_since(*date)
+                            .expect("found date that is after current month")
+                            >= min_months_since
+                    })
+                    .collect::<Vec<_>>(),
+            )
+        })
+        .filter(|(_, dates)| !dates.is_empty())
+}
+
+fn main() {
+    let root_dir = env::args()
+        .nth(1)
+        .expect("expect root Markdown directory as CLI argument");
+    let root_dir_path = Path::new(&root_dir);
+    let glob_pat = format!("{}/**/*.md", root_dir);
+    let today_chrono = Utc::today();
+    let current_month = Date {
+        year: today_chrono.year_ce().1,
+        month: today_chrono.month(),
+    };
+
+    let dates_by_file = collect_dates(glob(&glob_pat).unwrap().map(Result::unwrap));
+    let dates_by_file: BTreeMap<_, _> =
+        filter_dates(current_month, 6, dates_by_file.into_iter()).collect();
+
+    if dates_by_file.is_empty() {
+        println!("empty");
+    } else {
+        println!("Date Reference Triage for {}", current_month);
+        println!("## Procedure");
+        println!();
+        println!(
+            "Each of these dates should be checked to see if the docs they annotate are \
+             up-to-date. Each date should be updated (in the Markdown file where it appears) to \
+             use the current month ({current_month}), or removed if the docs it annotates are not \
+             expected to fall out of date quickly.",
+            current_month = current_month
+        );
+        println!();
+        println!(
+            "Please check off each date once a PR to update it (and, if applicable, its \
+             surrounding docs) has been merged. Please also mention that you are working on a \
+             particular set of dates so duplicate work is avoided."
+        );
+        println!();
+        println!("Finally, once all the dates have been updated, please close this issue.");
+        println!();
+        println!("## Dates");
+        println!();
+
+        for (path, dates) in dates_by_file {
+            println!(
+                "- [ ] {}",
+                path.strip_prefix(&root_dir_path).unwrap().display()
+            );
+            for (line, date) in dates {
+                println!("  - [ ] line {}: {}", line, date);
+            }
+        }
+        println!();
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn test_months_since() {
+        let date1 = Date {
+            year: 2020,
+            month: 3,
+        };
+        let date2 = Date {
+            year: 2021,
+            month: 1,
+        };
+        assert_eq!(date2.months_since(date1), Some(10));
+    }
+
+    #[test]
+    fn test_date_regex() {
+        let regex = make_date_regex();
+        assert!(regex.is_match("foo <!-- date: 2021-01 --> bar"));
+    }
+
+    #[test]
+    fn test_collect_dates_from_file() {
+        let text = "Test1\n<!-- date: 2021-01 -->\nTest2\nFoo<!-- date: 2021-02 \
+                    -->\nTest3\nTest4\nFoo<!-- date: 2021-03 -->Bar\n<!-- date: 2021-04 \
+                    -->\nTest5\nTest6\nTest7\n<!-- date: \n\n2021-05 -->\nTest8
+        ";
+        assert_eq!(
+            collect_dates_from_file(&make_date_regex(), text),
+            vec![
+                (
+                    2,
+                    Date {
+                        year: 2021,
+                        month: 1,
+                    }
+                ),
+                (
+                    4,
+                    Date {
+                        year: 2021,
+                        month: 2,
+                    }
+                ),
+                (
+                    7,
+                    Date {
+                        year: 2021,
+                        month: 3,
+                    }
+                ),
+                (
+                    8,
+                    Date {
+                        year: 2021,
+                        month: 4,
+                    }
+                ),
+                (
+                    14,
+                    Date {
+                        year: 2021,
+                        month: 5,
+                    }
+                ),
+            ]
+        );
+    }
+}