diff --git a/README.md b/README.md
index f29dbc3..e2bc9f4 100644
--- a/README.md
+++ b/README.md
@@ -1368,6 +1368,23 @@ Publishing is a separate step from building, and the separation is the point: th
 the site server reads is only touched once a build has succeeded, so a failed build
 leaves the previous site up rather than replacing it with a half-written one.
 
+**Two gates before the build starts.** The first waits for `/api/health` to answer 200,
+because `After=` orders a start and does not wait for a port. The second counts
+`/api/mints` and refuses to build below `MIN_MINTS_FOR_BUILD`, default 20.
+
+The second exists because health answering 200 and the index being complete are
+different claims. A year of ~31-event backfills left a perfectly healthy API serving a
+real, correct, complete list of eight mints; a build against that succeeds, prerenders
+eight cards, and `rsync --delete-after` replaces fifty-five with eight. The gate runs as
+an `ExecStartPre`, so a refusal aborts the unit before `pnpm build` — and publishing is
+`ExecStartPost`, after the build — which means the previously published site is never
+touched. The `OnFailure=` alert says why.
+
+```bash
+# Raise or lower it for this host without editing the unit:
+sudo systemctl edit cashumints-web        # [Service] / Environment=MIN_MINTS_FOR_BUILD=40
+```
+
 ```ini
 # /etc/systemd/system/cashumints-web.service
 [Unit]
@@ -1401,6 +1418,40 @@ Environment=PUBLIC_API_URL=
 # rather than letting the first fetch die on ECONNREFUSED. /api/health answers 503 until
 # it is genuinely ready, and curl -f treats that as a failure, so the loop keeps waiting.
 ExecStartPre=/usr/bin/timeout 90 /bin/sh -c 'until curl -sf -o /dev/null http://127.0.0.1:8788/api/health; do sleep 1; done'
+
+# Then: does the API actually have an index to build a site out of?
+#
+# Health answering 200 says the process is up and its last backfill read something. It
+# does not say how many mints are in the table, and those are different questions — the
+# year of ~31-event backfills had a healthy API serving a real, complete, correct list of
+# eight mints. A build against that succeeds, prerenders eight cards, and rsync happily
+# replaces fifty-five with eight.
+#
+# So count the list before spending twenty minutes building from it. Below the floor
+# this exits non-zero, systemd abandons the unit at ExecStartPre, and — because publishing
+# is ExecStartPost, after the build — the previously published site is never touched. The
+# site stays exactly as it was and the OnFailure alert says why.
+#
+# Counted by the `"host":` key, one per item, rather than by counting `{`: the list
+# payload carries a nested object per mint (its NUT capability switches), so brace
+# counting would report roughly double. No jq: it is not installed on this host and a
+# build gate should not add a dependency to run.
+#
+# `Q` is a double-quote character, built with printf rather than written literally,
+# because this whole command is already inside systemd's single quotes and a quote of
+# either kind in the grep pattern would end the argument early.
+#
+# A curl that fails for any reason leaves `n` empty, `$${n:-0}` reads that as zero, and
+# zero is below every floor — so an API that fell over between the health check above and
+# this line refuses the build rather than sailing through it.
+Environment=MIN_MINTS_FOR_BUILD=20
+ExecStartPre=/bin/sh -c 'Q=$$(printf "\\042"); \
+  n=$$(curl -sf --max-time 30 http://127.0.0.1:8788/api/mints | grep -o "$${Q}host$${Q}:" | wc -l); \
+  if [ "$${n:-0}" -lt "$$MIN_MINTS_FOR_BUILD" ]; then \
+    printf "<3>%s\\n" "refusing to build: /api/mints returned $${n:-0} mints, floor is $$MIN_MINTS_FOR_BUILD. Previous site left untouched."; \
+    exit 1; \
+  fi; \
+  printf "%s\\n" "build gate: $$n mints, floor $$MIN_MINTS_FOR_BUILD"'
 # Check `which pnpm` on the host: a corepack or pnpm-home install sits outside /usr/bin,
 # and systemd's PATH does not include it.
 ExecStart=/usr/bin/pnpm build
diff --git a/deploy/cashumints-web.service b/deploy/cashumints-web.service
index efe9020..627a79b 100644
--- a/deploy/cashumints-web.service
+++ b/deploy/cashumints-web.service
@@ -52,6 +52,40 @@ Environment=PUBLIC_API_URL=
 # rather than letting the first fetch die on ECONNREFUSED. /api/health answers 503 until
 # it is genuinely ready, and curl -f treats that as a failure, so the loop keeps waiting.
 ExecStartPre=/usr/bin/timeout 90 /bin/sh -c 'until curl -sf -o /dev/null http://127.0.0.1:8788/api/health; do sleep 1; done'
+
+# Then: does the API actually have an index to build a site out of?
+#
+# Health answering 200 says the process is up and its last backfill read something. It
+# does not say how many mints are in the table, and those are different questions — the
+# year of ~31-event backfills had a healthy API serving a real, complete, correct list of
+# eight mints. A build against that succeeds, prerenders eight cards, and rsync happily
+# replaces fifty-five with eight.
+#
+# So count the list before spending twenty minutes building from it. Below the floor
+# this exits non-zero, systemd abandons the unit at ExecStartPre, and — because publishing
+# is ExecStartPost, after the build — the previously published site is never touched. The
+# site stays exactly as it was and the OnFailure alert says why.
+#
+# Counted by the `"host":` key, one per item, rather than by counting `{`: the list
+# payload carries a nested object per mint (its NUT capability switches), so brace
+# counting would report roughly double. No jq: it is not installed on this host and a
+# build gate should not add a dependency to run.
+#
+# `Q` is a double-quote character, built with printf rather than written literally,
+# because this whole command is already inside systemd's single quotes and a quote of
+# either kind in the grep pattern would end the argument early.
+#
+# A curl that fails for any reason leaves `n` empty, `$${n:-0}` reads that as zero, and
+# zero is below every floor — so an API that fell over between the health check above and
+# this line refuses the build rather than sailing through it.
+Environment=MIN_MINTS_FOR_BUILD=20
+ExecStartPre=/bin/sh -c 'Q=$$(printf "\\042"); \
+  n=$$(curl -sf --max-time 30 http://127.0.0.1:8788/api/mints | grep -o "$${Q}host$${Q}:" | wc -l); \
+  if [ "$${n:-0}" -lt "$$MIN_MINTS_FOR_BUILD" ]; then \
+    printf "<3>%s\\n" "refusing to build: /api/mints returned $${n:-0} mints, floor is $$MIN_MINTS_FOR_BUILD. Previous site left untouched."; \
+    exit 1; \
+  fi; \
+  printf "%s\\n" "build gate: $$n mints, floor $$MIN_MINTS_FOR_BUILD"'
 # Check `which pnpm` on the host: a corepack or pnpm-home install sits outside /usr/bin,
 # and systemd's PATH does not include it.
 ExecStart=/usr/bin/pnpm build