diff --git a/.github/workflows/content-lint.yml b/.github/workflows/content-lint.yml
index f77c1d6d..865e4811 100644
--- a/.github/workflows/content-lint.yml
+++ b/.github/workflows/content-lint.yml
@@ -27,3 +27,64 @@ jobs:
 
       - name: Check per-page SEO front matter (description:)
         run: python scripts/check_seo_frontmatter.py
+
+  media-a11y:
+    # Source-level a11y conventions that html-proofer does NOT cover: YouTube
+    # iframe title=, <video> aria-label, and lazy empty alt (alt=""). See
+    # scripts/check_a11y.py. Complements the link-check job below.
+    runs-on: ubuntu-latest
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v4
+
+      - name: Setup Python
+        uses: actions/setup-python@v5
+        with:
+          python-version: "3.x"
+
+      - name: Check media a11y (iframe title, video aria-label, image alt)
+        run: python scripts/check_a11y.py --ci
+
+  link-check:
+    # Validate the BUILT site with html-proofer: broken internal links, broken
+    # anchors, missing image alt, and malformed HTML. External links are NOT
+    # checked here (slow/flaky); a separate non-blocking job can cover those.
+    runs-on: ubuntu-latest
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v4
+
+      - name: Setup Ruby
+        uses: ruby/setup-ruby@v1
+        with:
+          ruby-version: "3.3.11"
+          bundler-cache: true
+          cache-version: 0
+
+      - name: Build site (production baseurl)
+        run: bundle exec jekyll build --baseurl "/physcomp"
+        env:
+          JEKYLL_ENV: production
+
+      - name: Install html-proofer
+        run: gem install html-proofer -v 5.0.9
+
+      - name: Proof built site (internal links, anchors, image alt, HTML)
+        # --swap-urls strips the /physcomp baseurl so absolute internal links
+        # resolve against _site/. External link checking is disabled (slow/flaky).
+        #
+        # --ignore-files: each entry is tracked debt, not a silent skip:
+        #   * signals .+/index.html + IntroTo*.html -> stale generated nbconvert
+        #                                              notebooks               (issue #115)
+        #   * /arduino/accel.html          -> WIP draft, missing screenshot    (issue #115)
+        #   * /esp32/capacitive-touch.html -> WIP lesson, missing diagrams      (issue #114)
+        # Remove an entry once its issue is resolved so the gate covers that page.
+        # Each --ignore-files pattern must be wrapped in /slashes/ to be treated
+        # as a regex (a bare string is an exact-path match); internal slashes are
+        # escaped as \/.
+        run: |
+          htmlproofer ./_site \
+            --disable-external \
+            --swap-urls "^/physcomp:" \
+            --no-enforce-https \
+            --ignore-files "/\/signals\/.+\/index\.html/,/\/signals\/IntroTo[A-Za-z]+\.html/,/\/arduino\/accel\.html/,/\/esp32\/capacitive-touch\.html/"
diff --git a/_config.yml b/_config.yml
index 00879a94..b02a047f 100644
--- a/_config.yml
+++ b/_config.yml
@@ -102,7 +102,7 @@ callouts:
 # Aux links for the upper right navigation
 aux_links:
   "Makeability Lab":
-    - "//makeabilitylab.cs.washington.edu"
+    - "https://makeabilitylab.cs.washington.edu"
 
 # Heading anchor links appear on hover over h1-h6 tags in page content
 # allowing users to deep link to a particular heading on a page.
diff --git a/advancedio/assets/videos/AdafruitSTEMMAQT_IMG_6163-TrimmedAndCropped720p.mp4 b/advancedio/assets/videos/AdafruitSTEMMAQT_IMG_6163-TrimmedAndCropped720p.mp4
new file mode 100644
index 00000000..591c495b
Binary files /dev/null and b/advancedio/assets/videos/AdafruitSTEMMAQT_IMG_6163-TrimmedAndCropped720p.mp4 differ
diff --git a/advancedio/servo.md b/advancedio/servo.md
index aca3f334..a9f6af68 100644
--- a/advancedio/servo.md
+++ b/advancedio/servo.md
@@ -372,7 +372,7 @@ The Engineering Mindset YouTube channel did this for real with an oscilloscope,
 
 ### Activity 3: Sensor-driven servo gauge
 
-For our final activity, let's build a **physical gauge**—a servo-powered pointer that displays sensor data in the real world, like an analog speedometer or a VU meter needle. This is the physical output equivalent of the [OLED analog graph](oled.md#demo-3-basic-real-time-analog-graph) and the [NeoPixel level meter](addressable-leds.md#activity-4-led-level-meter). Where the OLED drew data on screen and the NeoPixels lit up LEDs proportionally, here we'll sweep a physical pointer across a scale.
+For our final activity, let's build a **physical gauge**—a servo-powered pointer that displays sensor data in the real world, like an analog speedometer or a VU meter needle. This is the physical output equivalent of the [OLED analog graph](oled.md#demo-3-basic-real-time-analog-graph) and the [NeoPixel level meter](addressable-leds.md). Where the OLED drew data on screen and the NeoPixels lit up LEDs proportionally, here we'll sweep a physical pointer across a scale.
 
 We'll read an analog sensor on `A0` and map it to the servo's range. To make it more interesting, we'll add two buttons: one to "freeze" the gauge at its current reading (like a max-hold feature on a multimeter), and one to reset it.
 
diff --git a/advancedio/smoothing-input.md b/advancedio/smoothing-input.md
index 82fb9187..7cb37633 100644
--- a/advancedio/smoothing-input.md
+++ b/advancedio/smoothing-input.md
@@ -157,7 +157,7 @@ You can find our full implementation on GitHub as [MovingAverageFilter.ino](http
 
 #### Simple C++ class
 
-Signal filtering is a perfect opportunity to create a class to hide complexity, avoid code redundancy, and handle data processing. In our [Makeability Lab Arduino Library](https://github.com/makeabilitylab/arduino/tree/master/MakeabilityLab_Arduino_Library/src), we created the [`MovingAveragefilter.hpp`](https://github.com/makeabilitylab/arduino/blob/master/MakeabilityLab_Arduino_Library/src/MovingAverageFilter.hpp) class, which simplifies using a moving average filter. But you could make your own, of course, or use [other libraries](#arduino-filtering-libraries.)
+Signal filtering is a perfect opportunity to create a class to hide complexity, avoid code redundancy, and handle data processing. In our [Makeability Lab Arduino Library](https://github.com/makeabilitylab/arduino/tree/master/MakeabilityLab_Arduino_Library/src), we created the [`MovingAveragefilter.hpp`](https://github.com/makeabilitylab/arduino/blob/master/MakeabilityLab_Arduino_Library/src/MovingAverageFilter.hpp) class, which simplifies using a moving average filter. But you could make your own, of course, or use [other libraries](#arduino-filtering-libraries)
 
 Here's a demonstration of how to use [`MovingAveragefilter.hpp`](https://github.com/makeabilitylab/arduino/blob/master/MakeabilityLab_Arduino_Library/src/MovingAverageFilter.hpp):
 
diff --git a/advancedio/vibromotor.md b/advancedio/vibromotor.md
index f726f34f..49e81192 100644
--- a/advancedio/vibromotor.md
+++ b/advancedio/vibromotor.md
@@ -608,7 +608,7 @@ In this lesson, you learned about vibration motors and how to safely control the
 
 ## Next Lesson
 
-In the [next lesson](../smoothing-input.md), we will switch from output to input and learn how to smooth noisy sensor data using digital signal processing techniques.
+In the [next lesson](smoothing-input.md), we will switch from output to input and learn how to smooth noisy sensor data using digital signal processing techniques.
 
 <nav class="lesson-nav" aria-label="Lesson navigation">
   <a href="servo.html" class="nav-prev">
diff --git a/arduino/buttons.md b/arduino/buttons.md
index 41a2e2fc..80615aff 100644
--- a/arduino/buttons.md
+++ b/arduino/buttons.md
@@ -181,7 +181,7 @@ However, if you do this, what will the digital input pin read when the switch is
 **Figure.** Animation of what happens when you press a button with the simple circuit configuration.
 {: .fs-1 }
 
-In fact, try wiring up this configuration yourself and running the following program with the [Serial Monitor](../electronics/serial-print#step-3-open-serial-monitor-in-the-arduino-ide) open. What happens when you press the button? Try touching the button legs with your fingers but not actually pressing the button—what happens to the `digitalRead` value? Are you reliably tracking the button state?
+In fact, try wiring up this configuration yourself and running the following program with the [Serial Monitor](serial-print.md#step-3-open-serial-monitor-in-the-arduino-ide) open. What happens when you press the button? Try touching the button legs with your fingers but not actually pressing the button—what happens to the `digitalRead` value? Are you reliably tracking the button state?
 
 {% highlight cpp %}
 const int INPUT_BUTTON_PIN = 2;
diff --git a/arduino/fast-analog-read.md b/arduino/fast-analog-read.md
index a5c7de7a..f1cbbe6d 100644
--- a/arduino/fast-analog-read.md
+++ b/arduino/fast-analog-read.md
@@ -10,7 +10,7 @@ usetocbot: true
 
 ## Speeding up the Arduino
 
-The Arduino `C` library attempts to provide an easy-to-understand and accessible API to program and use microcontrollers. However, this comes at a cost. There are a number of interesting online discussions and blog posts analyzing Arduino code and providing faster techniques for I/O. Importantly, as Willem Maes—a faculty of engineering in Belgium—notes in his [Speeding Up the Arduino]((http://www.optiloading.be/willem/Arduino/speeding.pdf)) document: 
+The Arduino `C` library attempts to provide an easy-to-understand and accessible API to program and use microcontrollers. However, this comes at a cost. There are a number of interesting online discussions and blog posts analyzing Arduino code and providing faster techniques for I/O. Importantly, as Willem Maes—a faculty of engineering in Belgium—notes in his [Speeding Up the Arduino](http://www.optiloading.be/willem/Arduino/speeding.pdf) document: 
 >the programmers who developed  Arduino weren't just lousy coders who couldn't write fast code, they consciously made the decision to add validations and safety checks since it benefits their target customers.
 
 ## How fast can we read data using analogRead and ATmega328? 
diff --git a/arduino/force-sensitive-resistors.md b/arduino/force-sensitive-resistors.md
index dab8b172..3052cac4 100644
--- a/arduino/force-sensitive-resistors.md
+++ b/arduino/force-sensitive-resistors.md
@@ -104,7 +104,7 @@ For more details, see the Interlink [FSR 402 datasheet]({{ site.baseurl }}/asset
 
 Let's make something!
 
-To begin, just like we did with the [buttons](buttons.md) and [potentiometers](potentiometers.md) lessons, we'll make a simple LED circuit without a microcontroller. In fact, this circuit will be the exact same as the "rheostat" potentiometer circuit [here](potentiometers.md#build-the-potentiometer-based-led-dimmer) (but we'll replace the rheostat with an FSR).
+To begin, just like we did with the [buttons](buttons.md) and [potentiometers](potentiometers.md) lessons, we'll make a simple LED circuit without a microcontroller. In fact, this circuit will be the exact same as the "rheostat" potentiometer circuit [here](potentiometers.md#step-1-build-the-potentiometer-based-led-dimmer) (but we'll replace the rheostat with an FSR).
 
 Below, we show two possible wiring diagrams: the first (preferred) shows the FSR circuit powered by a 9V battery while the second shows power derived from the 5V and GND pins on the Arduino. (Again, we prefer the former just to further emphasize that at this point, we're not using microcontrollers!)
 
diff --git a/arduino/led-blink3.md b/arduino/led-blink3.md
index 838f04d1..3dacb5f8 100644
--- a/arduino/led-blink3.md
+++ b/arduino/led-blink3.md
@@ -126,7 +126,7 @@ On the Arduino, the `unsigned long` data type is 32 bits (4 bytes), which ranges
 
 #### Blinking without delays logic
 
-We then use the same general logic as the "blinking without delays" [covered previously](led-blink#blink-without-using-delays) for each LED:
+We then use the same general logic as the "blinking without delays" [covered previously](led-blink.md#blink-without-using-delay) for each LED:
 
 {% highlight C %}
 unsigned long currentTimestampMs = millis();
diff --git a/arduino/led-on.md b/arduino/led-on.md
index d1b44544..c31988a6 100644
--- a/arduino/led-on.md
+++ b/arduino/led-on.md
@@ -20,7 +20,7 @@ usetocbot: true
 1. TOC
 {:toc}
 ---
-For our first learning activity, we are going to use Arduino to turn on an [LED]({{ site.baseurl }}/pages/electronics/leds.md). We're **not** going to write any code. Instead, our goal is to build some initial familiarity with Arduino hardware and connecting components to Arduino pins before we introduce programming, which we do in the [next lesson](led-blink.md).
+For our first learning activity, we are going to use Arduino to turn on an [LED](../electronics/leds.md). We're **not** going to write any code. Instead, our goal is to build some initial familiarity with Arduino hardware and connecting components to Arduino pins before we introduce programming, which we do in the [next lesson](led-blink.md).
 
 ![Animation showing a USB cable plugging into an Arduino Uno to power an LED + resistor hooked up to 5V and GND](assets/movies/Arduino_LEDOn_5VFixed_USBPower.gif)
 **Figure.** The movement of **current** in the circuit is illustrated by the animated yellow circles. This visualization is a coarse abstraction designed to emphasize the direction of current flow. A more accurate visualization would show that electrons are already distributed throughout a wire before a voltage is applied. See our [Introduction to Electronics](../electronics/index.md) series, specifically the lesson on [Voltage, Current, and Resistance](../electronics/electricity-basics.md).
diff --git a/arduino/potentiometers.md b/arduino/potentiometers.md
index 34b1d5b4..dbc2f516 100644
--- a/arduino/potentiometers.md
+++ b/arduino/potentiometers.md
@@ -219,7 +219,7 @@ Analog input!
 More formally, just like **analog output** enabled us to write out voltages between 0V and 5V, **analog input** enables us to **read voltages between 0V and 5V**. How does this work? Via an [ADC](https://en.wikipedia.org/wiki/Analog-to-digital_converter).
 
 <video autoplay loop muted playsinline aria-label="Animation comparing digital input which is either HIGH or LOW versus analog input which can be any voltage in between">
-  <source src="../electronics/assets/videos/AnalogVsDigital.mp4" type="video/mp4" />
+  <source src="assets/movies/AnalogVsDigital.mp4" type="video/mp4" />
 </video>
 **Video.** While digital input is simply HIGH (5V) or LOW (0V), analog can be anywhere in between. Our ability to sense gradations in the voltage signal is based on the resolution of the analog-to-digital converter. In the case of the Arduino Uno and Leonardo, this is 10 bits.
 {: .fs-1 }
diff --git a/cpx/analog-input.md b/cpx/analog-input.md
index 53ce3640..77560d25 100644
--- a/cpx/analog-input.md
+++ b/cpx/analog-input.md
@@ -69,7 +69,7 @@ It's OK if you don't understand exactly how voltage dividers work. The key is in
 
 In the above examples, we showed how to read 3.3V and GND (0V) with the CPX by touching the yellow wire to the red and black respectively and graphing the result. But analog input is far more interesting than just two numbers: 0 and 1023. How can we play with everything in between?
 
-We can do this by dividing the input voltage using resistors, which we cover in great detail in our [Electronics L4: Voltage Divider lesson](series-parallel.md#voltage-dividers) and touch on it a bit in the above video. We need not repeat ourselves here; however, if you want to experiment with manually controlling different input voltages on A1, try adding different resistor combinations like the following.
+We can do this by dividing the input voltage using resistors, which we cover in great detail in our [Electronics L4: Voltage Divider lesson](../electronics/series-parallel.md#voltage-dividers) and touch on it a bit in the above video. We need not repeat ourselves here; however, if you want to experiment with manually controlling different input voltages on A1, try adding different resistor combinations like the following.
 
 ![Intro to using a voltage divider with two resistors to control the input voltage on CPX pin A1](assets/images/CPX_IntroToVoltageDivider.png)
 
diff --git a/esp32/index.md b/esp32/index.md
index 69c54afe..935623d5 100644
--- a/esp32/index.md
+++ b/esp32/index.md
@@ -104,7 +104,7 @@ Use the ESP32's 12-bit ADC to read a potentiometer and control an LED's brightne
 
 Learn how to play tones and melodies on the ESP32 using the `tone()` function (now supported in ESP32 Arduino core v3.x!) and the LEDC PWM library.
 
-### [Lesson 6: Capacitive Touch Sensing](capacitive-touch-sensing.md)
+### [Lesson 6: Capacitive Touch Sensing](capacitive-touch.md)
 
 The ESP32 has built-in capacitive touch sensing hardware—no external components needed! In this lesson, you'll use a bare wire (or aluminum foil) as a touch sensor to control an LED.
 
diff --git a/esp32/iot.md b/esp32/iot.md
index c47747dc..e337e89d 100644
--- a/esp32/iot.md
+++ b/esp32/iot.md
@@ -183,7 +183,7 @@ Let's build our first IoT project! We'll read a photoresistor (light sensor), dr
 We have a photoresistor in a voltage divider with a 10kΩ resistor. The analog input voltage changes with the ambient light level. We also drive an LED via PWM, making it brighter as the room gets darker.
 
 {: .warning }
-> **ADC2 + WiFi conflict!** As we covered in the [Analog Input lesson](analog-input.md), the ESP32's ADC2 pins **cannot be used when WiFi is active**—this is a hardware limitation on all ESP32 variants. You must use **ADC1 pins** for any analog input in IoT projects. On the ESP32-S3 Feather, **A5** is the only "A"-labeled pin on ADC1. Pins labeled D5, D6, D9, and D10 are also ADC1 pins and can be used with `analogRead()` by passing their GPIO number. See the [Analog Input lesson](analog-input.md#which-pins-can-i-use) for full details.
+> **ADC2 + WiFi conflict!** As we covered in the [Analog Input lesson](analog-input.md), the ESP32's ADC2 pins **cannot be used when WiFi is active**—this is a hardware limitation on all ESP32 variants. You must use **ADC1 pins** for any analog input in IoT projects. On the ESP32-S3 Feather, **A5** is the only "A"-labeled pin on ADC1. Pins labeled D5, D6, D9, and D10 are also ADC1 pins and can be used with `analogRead()` by passing their GPIO number. See the [Analog Input lesson](analog-input.md#adc-pins-chip-vs-board) for full details.
 
 <!-- TODO: Create an updated Fritzing wiring diagram for the ESP32-S3 Feather with photoresistor + LED -->
 
diff --git a/esp32/tone.md b/esp32/tone.md
index 58f9d6cf..d7028dc6 100644
--- a/esp32/tone.md
+++ b/esp32/tone.md
@@ -645,14 +645,14 @@ In this lesson, you added sound to your ESP32 repertoire! Here's what you learne
 
 ## Next Lesson
 
-In the [next lesson](capacitive-touch-sensing.md), we'll learn about the ESP32's built-in capacitive touch sensing hardware—no external components needed! You'll use touch inputs to trigger tones and build a simple touch piano.
+In the [next lesson](capacitive-touch.md), we'll learn about the ESP32's built-in capacitive touch sensing hardware—no external components needed! You'll use touch inputs to trigger tones and build a simple touch piano.
 
 <nav class="lesson-nav" aria-label="Lesson navigation">
   <a href="analog-input.html" class="nav-prev">
     <div class="nav-label">&larr; Previous Lesson</div>
     <div class="nav-title">Analog input</div>
   </a>
-  <a href="capacitive-touch-sensing.html" class="nav-next">
+  <a href="capacitive-touch.html" class="nav-next">
     <div class="nav-label">Next Lesson &rarr;</div>
     <div class="nav-title">Capacitive touch sensing</div>
   </a>
diff --git a/scripts/README.md b/scripts/README.md
index b6966777..e713a90d 100644
--- a/scripts/README.md
+++ b/scripts/README.md
@@ -27,7 +27,7 @@ Python utilities that bulk-edit or generate content across the textbook. They ar
 | [`fix_embedded_media.py`](fix_embedded_media.py) | Normalize `<video>` inline styles and wrap bare YouTube iframes responsively. | `--run` |
 | [`update_lesson_nav.py`](update_lesson_nav.py) | Migrate old `.btn` lesson nav to card-style `<nav class="lesson-nav">` (rewrites `.md`→`.html`). | `--run` |
 | [`fix_arduino_urls.py`](fix_arduino_urls.py) | Migrate old `arduino.cc` URLs to `docs.arduino.cc`. **Untested/brittle — use with care.** | `--apply` |
-| [`check_a11y.py`](check_a11y.py) | **Deprecated** local-only a11y spot-check (iframe `title`, video `aria-label`, image alt). **Not a CI gate** — superseded by html-proofer. Read-only. | _(none)_ |
+| [`check_a11y.py`](check_a11y.py) | **CI gate** — fail if a published page has a YouTube `<iframe>` w/o `title=`, a `<video>` w/o `aria-label`, or an image with empty/missing alt. Complements html-proofer (which can't see these). Read-only. | _(none)_ |
 
 ## Details
 
@@ -89,23 +89,26 @@ python scripts/update_lesson_nav.py           # dry run
 python scripts/update_lesson_nav.py --run      # apply
 ```
 
-### `check_a11y.py` (deprecated)
+### `check_a11y.py`
 
-A fast, dependency-free local spot-check for three source-level a11y patterns:
-YouTube `<iframe>`s missing `title=`, `<video>`s missing `aria-label`, and images
-with empty alt (`![](...)`). Same published-page scope and draft/contributor
-exemptions as `check_seo_frontmatter.py`.
+Enforces three source-level accessibility conventions on published pages: YouTube
+`<iframe>`s must have a `title=`, `<video>`s must have an `aria-label`, and images
+must have non-empty alt text (`![](...)` is flagged). Same published-page scope and
+draft/contributor exemptions as `check_seo_frontmatter.py`; prints ASCII only.
 
-> **Not a CI gate.** Content QA is moving to the off-the-shelf, Jekyll-native
-> [`html-proofer`](https://github.com/gjtorikian/html-proofer) gem (checks missing
-> image alt, broken links, and malformed HTML against the built `_site/`, with no
-> new toolchain). Do **not** wire this script into `content-lint.yml`; once
-> html-proofer is in place it can be deleted (see issue #110).
+Run by the **Content lint** workflow (`media-a11y` job) via `--ci`. It is the a11y
+analogue of the SEO gate — a small policy check for conventions with **no
+off-the-shelf equivalent**, and deliberately **complementary** to html-proofer
+(the `link-check` job): html-proofer validates the *built* site (broken
+links/anchors, missing-alt, HTML) but permits empty `alt=""` and has no concept of
+iframe titles or video aria-labels, so it cannot enforce these three. Scanning the
+markdown *source* (not rendered HTML) also avoids false positives on the theme's
+decorative images.
 
 ```bash
 python scripts/check_a11y.py            # full report, grouped by module
 python scripts/check_a11y.py --summary  # per-module counts only
-python scripts/check_a11y.py --ci       # exit 1 if any issue (local spot-check)
+python scripts/check_a11y.py --ci       # exit 1 if any issue (CI gate)
 ```
 
 ### `fix_arduino_urls.py`
diff --git a/scripts/check_a11y.py b/scripts/check_a11y.py
index e7d2e535..1893e350 100644
--- a/scripts/check_a11y.py
+++ b/scripts/check_a11y.py
@@ -1,13 +1,15 @@
 """
-check_a11y.py — quick local accessibility audit for embedded media and images.
-
-    DEPRECATED — NOT a CI gate. We are standardizing on the off-the-shelf,
-    Jekyll-native html-proofer gem (run against the built _site/) for content
-    QA — it checks missing image alt, broken links, and malformed HTML, with no
-    new toolchain. This bespoke checker is kept only as a fast, dependency-free
-    local spot-check for the three source-level patterns below. Do NOT wire it
-    back into `.github/workflows/content-lint.yml`; once html-proofer is in place
-    and proven, this script can be deleted. See issue #110.
+check_a11y.py — CI gate for source-level media accessibility conventions.
+
+Complements html-proofer (the Content lint "link-check" job). html-proofer
+validates the BUILT site (broken links/anchors, missing-alt, HTML validity) but
+deliberately does NOT enforce the authoring conventions below: it permits empty
+`alt=""` (spec-correct "decorative" default, `ignore_empty_alt: true`) and has no
+concept of iframe titles or video aria-labels. This script gates those three
+markdown-SOURCE conventions, scanning published .md pages only (so it never
+false-positives on theme/decorative images). It is the a11y analogue of
+check_seo_frontmatter.py: a small policy check for conventions that have no
+off-the-shelf equivalent.
 
 Scans published .md pages for three common, mechanically-detectable a11y gaps:
 
@@ -25,9 +27,9 @@
 Modes:
     python scripts/check_a11y.py            # full report, grouped by module (exit 0)
     python scripts/check_a11y.py --summary  # per-module counts only
-    python scripts/check_a11y.py --ci       # exit 1 if any issue found (local spot-check only)
+    python scripts/check_a11y.py --ci       # exit 1 if any issue found (CI gate)
 
-Prints ASCII only (avoids cp1252 crashes on Windows consoles).
+Prints ASCII only (avoids cp1252 crashes in CI logs / Windows consoles).
 """
 
 import re
diff --git a/sensors/hall-effect.md b/sensors/hall-effect.md
index 8ab61b68..cd5d075d 100644
--- a/sensors/hall-effect.md
+++ b/sensors/hall-effect.md
@@ -190,7 +190,7 @@ My vocal narration is quite soft as I recorded the video early in the morning an
 ### Improving the circuit
 
 What if we wanted to supply more than 1mA through our LED? We have have two choices: 
-1. Just like with our [photoresistor](photoresistors.md#An-improved-auto-on-nightlight-circuit) circuit, we could change our circuit to use a **transistor**. In this case, the Hall effect sensor output would be connected to a transistor, which would control the current through our LED. If you have a transistor, feel free to try this!
+1. Just like with our [photoresistor](photoresistors.md#an-improved-auto-on-nightlight-circuit) circuit, we could change our circuit to use a **transistor**. In this case, the Hall effect sensor output would be connected to a transistor, which would control the current through our LED. If you have a transistor, feel free to try this!
 2. We could move on to using a microcontroller, which is what we're going to do!
 
 ## Make an Arduino-based magical magnetic LED brightener
diff --git a/website-dev.md b/website-dev.md
index d0eae0d6..e4a92855 100644
--- a/website-dev.md
+++ b/website-dev.md
@@ -28,7 +28,7 @@ Assuming you have the prerequisite libraries and software infrastructure (e.g.,
 
 The live site at <https://makeabilitylab.github.io/physcomp/> is built and
 published by the GitHub Actions workflow in
-[`.github/workflows/jekyll.yml`](.github/workflows/jekyll.yml). On every push to
+[`.github/workflows/jekyll.yml`](https://github.com/makeabilitylab/physcomp/blob/main/.github/workflows/jekyll.yml). On every push to
 `main` (and on manual runs from the **Actions** tab), the workflow runs
 `bundle exec jekyll build` on a clean Ubuntu runner and deploys the resulting
 `_site/` to GitHub Pages with `actions/deploy-pages`.
@@ -139,6 +139,49 @@ set for you) with:
 python scripts/generate_og_posters.py --run <module>/<your-page>.md
 ```
 
+## Accessibility and content QA
+
+Two CI checks in the **Content lint** workflow guard accessibility and link health.
+They are complementary — neither subsumes the other:
+
+| Check (job) | Tool | Runs against | Catches |
+|---|---|---|---|
+| `media-a11y` | `scripts/check_a11y.py` | Markdown **source** | YouTube `<iframe>` without `title=`, `<video>` without `aria-label`, image with empty/missing alt |
+| `link-check` | [`html-proofer`](https://github.com/gjtorikian/html-proofer) | built **`_site/`** | broken internal links, broken `#anchors`, missing `alt` attribute, malformed HTML |
+
+We use the off-the-shelf `html-proofer` for the commodity problem (links/HTML);
+`check_a11y.py` only covers the source conventions html-proofer can't see (it permits
+empty `alt=""` as "decorative" and has no notion of iframe titles or video labels).
+
+**Authoring rules** (all enforced):
+
+- **YouTube embeds** — give the `<iframe>` a `title=` describing the video, e.g.
+  `<iframe title="An RGB LED fading between colors" src="https://www.youtube.com/embed/…" …>`.
+- **`<video>` heroes/demos** — add an `aria-label=` describing the clip.
+- **Images** — informative images need descriptive alt: `![what it shows](path.png)`.
+  Don't start with "Image of"; don't dump the filename. A genuinely *decorative* image
+  may use empty `alt=""`, but `check_a11y` flags `![](…)` in source, so make alt explicit.
+- **Drafts / WIP** — a page that intentionally references not-yet-created assets should be
+  `nav_exclude: true` (the `media-a11y` check skips drafts). If a published page must keep a
+  not-yet-added asset, add its built path to the `--ignore-files` list in
+  `content-lint.yml` **with a tracking issue** (don't ignore silently).
+
+**Running html-proofer locally.** It needs `libcurl` (via `typhoeus`/`ethon`), which isn't
+present on stock Windows — so it runs in CI (Ubuntu) but may fail to even load on native
+Win11 (`Could not open library 'libcurl'`). Options: rely on CI; run it under **WSL2 or
+macOS** (libcurl present, matches CI); or on native Win11 install it once with
+`ridk exec pacman -S mingw-w64-ucrt-x86_64-curl`. To run it (after a build):
+
+```bash
+bundle exec jekyll build --baseurl "/physcomp"
+gem install html-proofer -v 5.0.9
+htmlproofer ./_site --disable-external --swap-urls "^/physcomp:" \
+  --ignore-files "/\/signals\/.+\/index\.html/,/\/signals\/IntroTo[A-Za-z]+\.html/,/\/arduino\/accel\.html/,/\/esp32\/capacitive-touch\.html/"
+```
+
+`check_a11y.py` is pure Python (no libcurl) and runs anywhere:
+`python scripts/check_a11y.py` (add `--summary` for counts, `--ci` to fail on any issue).
+
 ## Code highlighting
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