diff --git a/README.md b/README.md
index a846d52..93d8272 100644
--- a/README.md
+++ b/README.md
@@ -1,22 +1,203 @@
 # benchmark.fyi
 
-This project is a place to share benchmark-ips data for all your benchmarks
+Share [benchmark-ips](https://github.com/evanphx/benchmark-ips) results as a URL instead of a screenshot.
 
-## Getting Started
+Hosted instance: **https://ips.fastruby.io**
 
-You can locally setup this Rails application by calling this command:
+## Why
 
+`benchmark-ips` measures how many iterations per second your Ruby code manages, and prints a table to your terminal:
+
+```
+Warming up --------------------------------------
+      string concat    1.234M i/100ms
+Calculating -------------------------------------
+      string concat   12.345M (± 1.2%) i/s -     61.725M in   5.001234s
+```
+
+That output is awkward to share. Pasting it into an issue loses the formatting, and a screenshot can't be compared against anything.
+
+This app takes the same data and gives you a short link that renders it as a table, bolds the fastest entry, flags entries whose standard deviation is high enough to distrust, and optionally shows how many times slower each entry is than the winner. Useful in a bug report, a PR description, or a blog post about a performance fix.
+
+## Sharing a benchmark
+
+Install the gem:
+
+```ruby
+# Gemfile
+gem 'benchmark-ips'
+```
+
+Write a benchmark. Each `x.report` block is one entry in the shared table, and
+`x.compare!` adds the times-slower column:
+
+```ruby
+require 'benchmark/ips'
+
+Benchmark.ips do |x|
+  # Optional. Defaults are 2s warmup and 5s per report.
+  x.config(warmup: 1, time: 2)
+
+  a, b, c = "a", "b", "c"
+
+  x.report("interpolation") { "#{a}#{b}#{c}" }
+  x.report("concat (+)")    { a + b + c }
+  x.report("<< buffer")     { (+"") << a << b << c }
+  x.report("format")        { format("%s%s%s", a, b, c) }
+
+  # Adds the "times slower" column to the shared report.
+  x.compare!
+end
+```
+
+Two ready-to-run files live in `examples/`:
+
+| File | What it is for |
+|---|---|
+| `examples/smoke_benchmark.rb` | The benchmark above. Checks that an instance accepts and renders a report. |
+| `examples/legacy_client_benchmark.rb` | Same, pinned to benchmark-ips 2.14.0, to exercise the pre-2.15.0 request shape. |
+
+```bash
+ruby examples/smoke_benchmark.rb
+```
+
+Run it with `SHARE=1`:
+
+```bash
+SHARE=1 ruby my_benchmark.rb
+```
+
+The gem POSTs the results and prints the URL:
+
+```
+Shared at: https://ips.fastruby.io/2Bq
+```
+
+Report ids are base58-encoded row ids, so early ones on a fresh instance are a
+single character (`/2`, `/3`). That is a real link, not a truncated one.
+
+To send results to your own instance instead, set `SHARE_URL` (which enables sharing on its own, no `SHARE` needed):
+
+```bash
+SHARE_URL=http://localhost:3000 ruby my_benchmark.rb
 ```
+
+## Running it locally
+
+Requirements:
+
+- Ruby **4.0.6** (see `.tool-versions`)
+- PostgreSQL
+
+`config/database.yml` is intentionally not in the repo, so a fresh clone has to
+create one. Both `bin/setup` and `bin/dev` stop with the command to run if it is
+missing, so you do not have to remember this.
+
+Install dependencies and create the databases:
+
+```bash
 ./bin/setup
 ```
 
-## Submitting Data
+Start the server:
+
+```bash
+bin/dev
+```
+
+Arguments pass through, so `bin/dev -p 4000` works. There is no asset watcher to
+run alongside the server, so this is a plain wrapper around `bin/rails server`,
+not the foreman-and-`Procfile.dev` version Rails generates for apps that have
+one.
+
+Visit http://localhost:3000 and share a benchmark at it using the `SHARE_URL` example above.
 
-In order to submit data to your local instance, you can do it like this:
+## Verifying a change end to end
 
+The suite uses Rack::Test, so it never exercises the real server or a real
+client. To check a change for real, start the app and point an actual benchmark
+at it:
+
+```bash
+bin/dev
+SHARE_URL=http://localhost:3000 ruby examples/smoke_benchmark.rb
+```
+
+Then confirm what was stored:
+
+```bash
+bin/rails runner 'r = Report.last; puts r.short_id; puts r.entries.map { |e| e["name"] }.inspect'
 ```
-SHARE_URL=http://localhost:3000 ruby my-awesome-benchmark-ips-example.rb
+
+The same works against a deployed instance, which is how a review app gets
+checked:
+
+```bash
+SHARE_URL=https://your-app.herokuapp.com ruby my_benchmark.rb
+heroku logs --tail -a your-app
+heroku run --no-tty -a your-app -- bin/rails runner 'puts Report.count'
 ```
 
+## Tests
+
+```bash
+bin/rails test
+```
+
+The app dual-boots so the next Rails version can be tested before committing to it. `Gemfile` tracks Rails 7.1 and `Gemfile.next` tracks 7.2; CI runs both. To run the suite against the next version:
+
+```bash
+BUNDLE_GEMFILE=Gemfile.next bundle install
+BUNDLE_GEMFILE=Gemfile.next bin/rails test
+```
+
+## The API
+
+`POST /reports` with a JSON body. Each entry needs `name`, `ips`, `stddev`, `microseconds`, `iterations` and `cycles`; anything missing gets a 400. `central_tendency` and `error` are accepted and optional, as are the top-level `ruby`, `os` and `arch` fields.
+
+```json
+{
+  "entries": [
+    {
+      "name": "concat",
+      "ips": 12345678.9,
+      "stddev": 123456.7,
+      "microseconds": 5001234.0,
+      "iterations": 61725000,
+      "cycles": 1234000
+    }
+  ],
+  "options": { "compare": true }
+}
+```
+
+The response is the report's short id, which is also its path:
+
+```json
+{ "id": "2Bq" }
+```
+
+`GET /:id` renders that report.
+
+`benchmark-ips` before 2.15.0 sent this body with no content type, and
+`Net::HTTP` then supplied `application/x-www-form-urlencoded`, so Rails parsed
+the JSON as form data. `ReportsController#fix_missing_json_content_type` repairs
+that by re-reading the raw body, which only works while rack rewinds
+`rack.input` after form parsing. Rack 2.x does, rack 3 does not. That is why
+`rack` is pinned to `~> 2.2`, and `test/integration/create_report_test.rb`
+covers both request shapes.
+
+If you touch that code path, test it against a real old client with
+`examples/legacy_client_benchmark.rb`. Installing the old gem is not enough on
+its own, because `require` activates the newest installed version, so that file
+pins it at require time with `gem 'benchmark-ips', '2.14.0'`.
+
+A legacy request logs `Parameters: {"{\"entries\":" => ...}` before the repair
+runs; a modern one logs properly parsed JSON. That log line is how you tell
+which path you actually exercised.
+
+## Contributing
 
+Issues and pull requests welcome at https://github.com/fastruby/benchmark.fyi. Please make sure `bin/rails test` passes against both `Gemfile` and `Gemfile.next`.
 
+Originally built by Evan Phoenix ([evanphx](https://github.com/evanphx)), who also wrote `benchmark-ips`. [FastRuby.io](https://www.fastruby.io) maintains this app and the hosted instance.
diff --git a/babel.config.js b/babel.config.js
deleted file mode 100644
index 12f98da..0000000
--- a/babel.config.js
+++ /dev/null
@@ -1,72 +0,0 @@
-module.exports = function(api) {
-  var validEnv = ['development', 'test', 'production']
-  var currentEnv = api.env()
-  var isDevelopmentEnv = api.env('development')
-  var isProductionEnv = api.env('production')
-  var isTestEnv = api.env('test')
-
-  if (!validEnv.includes(currentEnv)) {
-    throw new Error(
-      'Please specify a valid `NODE_ENV` or ' +
-        '`BABEL_ENV` environment variables. Valid values are "development", ' +
-        '"test", and "production". Instead, received: ' +
-        JSON.stringify(currentEnv) +
-        '.'
-    )
-  }
-
-  return {
-    presets: [
-      isTestEnv && [
-        '@babel/preset-env',
-        {
-          targets: {
-            node: 'current'
-          }
-        }
-      ],
-      (isProductionEnv || isDevelopmentEnv) && [
-        '@babel/preset-env',
-        {
-          forceAllTransforms: true,
-          useBuiltIns: 'entry',
-          corejs: 3,
-          modules: false,
-          exclude: ['transform-typeof-symbol']
-        }
-      ]
-    ].filter(Boolean),
-    plugins: [
-      'babel-plugin-macros',
-      '@babel/plugin-syntax-dynamic-import',
-      isTestEnv && 'babel-plugin-dynamic-import-node',
-      '@babel/plugin-transform-destructuring',
-      [
-        '@babel/plugin-proposal-class-properties',
-        {
-          loose: true
-        }
-      ],
-      [
-        '@babel/plugin-proposal-object-rest-spread',
-        {
-          useBuiltIns: true
-        }
-      ],
-      [
-        '@babel/plugin-transform-runtime',
-        {
-          helpers: false,
-          regenerator: true,
-          corejs: false
-        }
-      ],
-      [
-        '@babel/plugin-transform-regenerator',
-        {
-          async: false
-        }
-      ]
-    ].filter(Boolean)
-  }
-}
diff --git a/bin/dev b/bin/dev
new file mode 100755
index 0000000..7a720dc
--- /dev/null
+++ b/bin/dev
@@ -0,0 +1,18 @@
+#!/usr/bin/env sh
+set -e
+
+# There is no asset watcher to run alongside the server, so this is a plain
+# launcher rather than the foreman + Procfile.dev version Rails generates.
+
+if [ ! -f config/database.yml ]; then
+  echo "config/database.yml is missing, so the server cannot start."
+  echo
+  echo "  cp config/database.yml.github config/database.yml"
+  echo
+  echo "That template expects a 'postgres' role over TCP, which suits CI. If you"
+  echo "run PostgreSQL locally under your own account, delete the username,"
+  echo "password and host lines from it."
+  exit 1
+fi
+
+exec bin/rails server "$@"
diff --git a/bin/setup b/bin/setup
index 02e96c0..778122f 100755
--- a/bin/setup
+++ b/bin/setup
@@ -24,6 +24,18 @@ FileUtils.chdir APP_ROOT do
   #   FileUtils.cp 'config/database.yml.sample', 'config/database.yml'
   # end
 
+  unless File.exist?('config/database.yml')
+    abort <<~MSG
+      \n== config/database.yml is missing, so the database cannot be prepared ==
+
+        cp config/database.yml.github config/database.yml
+
+      That template expects a 'postgres' role over TCP, which suits CI. If you
+      run PostgreSQL locally under your own account, delete the username,
+      password and host lines from it.
+    MSG
+  end
+
   puts "\n== Preparing database =="
   system! 'bin/rails db:prepare'
 
diff --git a/examples/legacy_client_benchmark.rb b/examples/legacy_client_benchmark.rb
new file mode 100644
index 0000000..fd7278f
--- /dev/null
+++ b/examples/legacy_client_benchmark.rb
@@ -0,0 +1,23 @@
+# Same as smoke_benchmark.rb, but forces the pre-2.15.0 client, which sends a
+# JSON body with a form content type instead of application/json. Use this to
+# exercise ReportsController#fix_missing_json_content_type.
+#
+#   gem install benchmark-ips -v 2.14.0
+#   SHARE_URL=http://localhost:3000 ruby examples/legacy_client_benchmark.rb
+#
+# The `gem` call is required: `require` alone activates the newest installed
+# version, so installing 2.14.0 next to a newer gem is not enough.
+
+gem 'benchmark-ips', '2.14.0'
+require 'benchmark/ips'
+
+Benchmark.ips do |x|
+  x.config(warmup: 1, time: 2)
+
+  a, b, c = "a", "b", "c"
+
+  x.report("interpolation") { "#{a}#{b}#{c}" }
+  x.report("concat (+)")    { a + b + c }
+
+  x.compare!
+end
diff --git a/examples/smoke_benchmark.rb b/examples/smoke_benchmark.rb
new file mode 100644
index 0000000..1801863
--- /dev/null
+++ b/examples/smoke_benchmark.rb
@@ -0,0 +1,26 @@
+# A small benchmark for checking that an instance of benchmark.fyi accepts and
+# renders a report. Compares four ways of building the same string.
+#
+#   gem install benchmark-ips
+#   SHARE_URL=http://localhost:3000 ruby examples/smoke_benchmark.rb
+#
+# Drop SHARE_URL and use SHARE=1 to share to https://ips.fastruby.io instead.
+
+require 'benchmark/ips'
+
+Benchmark.ips do |x|
+  # The defaults are 2s warmup and 5s per report, which is slower than a smoke
+  # test needs. Raise these when you care about the numbers.
+  x.config(warmup: 1, time: 2)
+
+  a, b, c = "a", "b", "c"
+
+  x.report("interpolation") { "#{a}#{b}#{c}" }
+  x.report("concat (+)")    { a + b + c }
+  x.report("<< buffer")     { (+"") << a << b << c }
+  x.report("format")        { format("%s%s%s", a, b, c) }
+
+  # Adds the "times slower" column to the shared report. Without this the
+  # report renders name and iterations/second only.
+  x.compare!
+end
diff --git a/postcss.config.js b/postcss.config.js
deleted file mode 100644
index aa5998a..0000000
--- a/postcss.config.js
+++ /dev/null
@@ -1,12 +0,0 @@
-module.exports = {
-  plugins: [
-    require('postcss-import'),
-    require('postcss-flexbugs-fixes'),
-    require('postcss-preset-env')({
-      autoprefixer: {
-        flexbox: 'no-2009'
-      },
-      stage: 3
-    })
-  ]
-}