diff --git a/README.md b/README.md
index 9d141d3..7ad228e 100644
--- a/README.md
+++ b/README.md
@@ -35,6 +35,11 @@ HTTP API providing user/client message handling for an fmsg host. Exposes CRUD o
 Standard PostgreSQL environment variables (`PGHOST`, `PGPORT`, `PGUSER`,
 `PGPASSWORD`, `PGDATABASE`) are used for database connectivity.
 
+fmsg-webapi assumes [fmsgd](https://github.com/markmnl/fmsgd) is the fmsg host
+implementation and uses the same PostgreSQL database. The fmsgd schema remains
+the base schema; this repository's [dd.sql](dd.sql) adds the API-key and
+delegation tables used by fmsg-webapi.
+
 A `.env` file placed in the working directory is loaded automatically at startup
 (values in the environment take precedence).
 
@@ -106,7 +111,7 @@ X-FMSG-Act-As: @user_bot@example.com
 The requested address must be granted to the authenticated user and must exist
 in fmsgid.
 
-Apply [api_keys.sql](api_keys.sql) before enabling API-key auth. Existing
+Apply [dd.sql](dd.sql) before enabling API-key auth. Existing
 deployments that already applied the earlier API-key table should apply
 [api_keys_delegation.sql](api_keys_delegation.sql).
 
diff --git a/api_keys.sql b/dd.sql
similarity index 85%
rename from api_keys.sql
rename to dd.sql
index 6915de8..c9f9e2b 100644
--- a/api_keys.sql
+++ b/dd.sql
@@ -1,3 +1,11 @@
+-- fmsg-webapi database extensions.
+--
+-- This file extends the fmsgd schema at:
+-- https://github.com/markmnl/fmsgd/blob/main/dd.sql
+--
+-- fmsg-webapi assumes fmsgd is the fmsg host implementation and uses the same
+-- PostgreSQL database.
+
 CREATE TABLE IF NOT EXISTS fmsg_api_sub_account (
     owner_addr varchar(255) NOT NULL,
     agent varchar(64) NOT NULL,