diff --git a/README.md b/README.md
index c1f1ba1..9dd32bc 100644
--- a/README.md
+++ b/README.md
@@ -28,7 +28,7 @@ Quota and context turn yellow from 50% and red from 80%. The costs, quota and ag
 
 Before you run `shelltime init`, it still shows git, model, session cost, quota and context. Daily cost and agent time show `-`, and nothing is sent to ShellTime. The line refreshes as the conversation moves on, not while the session is idle.
 
-When Claude opens a pull request with `gh pr create`, the mod links that PR to the session on shelltime.xyz. This goes through the `shelltime` CLI and its daemon.
+When Claude opens a pull request with `gh pr create`, the mod links that PR to the session on shelltime.xyz. This goes through the `shelltime` CLI and its daemon. If the repository has the ShellTime GitHub App installed, ShellTime also comments on the PR with the session's tokens, cost and time, and a link to the session.
 
 The [mod's README](plugins/shelltime-statusline/README.md) has every segment's colors and where each number comes from.
 
diff --git a/plugins/shelltime-statusline/README.md b/plugins/shelltime-statusline/README.md
index a2aa994..bdea0db 100644
--- a/plugins/shelltime-statusline/README.md
+++ b/plugins/shelltime-statusline/README.md
@@ -67,6 +67,27 @@ The CLI hands the URLs to the ShellTime daemon, which sends them to ShellTime, a
 - If the CLI can't be found, or is too old to have `cc pr`, nothing is linked. Errors from the CLI itself (not logged in, server unreachable) go to `~/.shelltime/log.log`.
 - This runs from a `PostToolUse` hook, in the background, after the tool returns. It never delays or changes the Bash result Claude sees.
 
+### Session cost comment
+
+If the ShellTime GitHub App is installed on the repository, ShellTime comments on each linked github.com PR, as the app. The comment shows:
+
+- the session's cost in USD
+- tokens: total, input, output, cache read and cache write
+- duration and active time
+- the model
+- prompts and lines changed
+- a link to the session on shelltime.xyz, which only you can open
+
+The comment is posted a couple of minutes after the PR is linked. ShellTime edits the same comment 30 minutes and 24 hours later, so it ends with the whole session's numbers.
+
+- If you turned off showing your AI cost publicly on shelltime.xyz, the comment leaves out the USD amounts.
+- Delete the comment and it is not posted again.
+- Only PRs opened by a GitHub account linked to your ShellTime account get a comment. If you signed in to ShellTime without GitHub, link your GitHub account first.
+- Without the app on the repository, nothing is posted.
+- Nothing is posted for GitHub Enterprise hosts.
+
+The mod and the CLI do nothing extra for this: ShellTime's server posts the comment once the PR is linked.
+
 ## Terminal
 
 If `~/.claude/settings.json` also has a `statusLine` running `shelltime cc statusline`, the terminal shows both lines. Keep both, or remove one.