diff --git a/hledger-web/hledger-web.m4.md b/hledger-web/hledger-web.m4.md
index 473f0f1ab..548299f75 100644
--- a/hledger-web/hledger-web.m4.md
+++ b/hledger-web/hledger-web.m4.md
@@ -260,6 +260,9 @@ Most of the JSON corresponds to hledger's data types; for details of what the fi
 and click on the various data types, eg 
 [Transaction](https://hackage.haskell.org/package/hledger-lib-1.17.1/docs/Hledger-Data-Types.html#t:Transaction).
 And for a higher level understanding, see the [journal docs](hledger.html#journal).
+There is also a basic [OpenAPI specification][openapi.yaml].
+
+[openapi.yaml]: https://github.com/simonmichael/hledger/blob/master/hledger-web/config/openapi.yaml
 
 In some cases there is outer JSON corresponding to a "Report" type.
 To understand that, go to the
diff --git a/hledger/hledger.m4.md b/hledger/hledger.m4.md
index 000b94a2d..2f4bb9135 100644
--- a/hledger/hledger.m4.md
+++ b/hledger/hledger.m4.md
@@ -604,6 +604,7 @@ Some notes about the various output formats:
   representation of hledger's internal data types. To understand the
   JSON, read the Haskell type definitions, which are mostly in
   <https://github.com/simonmichael/hledger/blob/master/hledger-lib/Hledger/Data/Types.hs>.
+  [hledger-web's OpenAPI specification][openapi.yaml] may also be relevant.
 
 <!--
 - The JSON output from hledger commands is essentially the same as the
@@ -626,6 +627,8 @@ Some notes about the various output formats:
   find otherwise, please let us know. 
   (Cf [#1195](https://github.com/simonmichael/hledger/issues/1195))
 
+[openapi.yaml]: https://github.com/simonmichael/hledger/blob/master/hledger-web/config/openapi.yaml
+
 ### SQL output
 
 - This is not yet much used; real-world feedback is welcome.