diff --git a/format/seat-definition.schema.json b/format/seat-definition.schema.json
new file mode 100644
index 0000000..965beeb
--- /dev/null
+++ b/format/seat-definition.schema.json
@@ -0,0 +1,419 @@
+{
+  "$schema": "https://json-schema.org/draft/2020-12/schema",
+  "$id": "https://git.novox.be/novox/mesh-contracts/format/seat-definition.schema.json",
+  "title": "A seat's definition (novox/hq ADR 0608 \u00a71, design 26), format 1",
+  "description": "One file per seat, seats/<seat>/seat.json. A whole definition (grain whole) gives every verb's input and answer, every message's body and where its events are kept; one at the seat list's grain (seat-list) holds what mesh-sdk's compiled seat list held (ADR 0613 \u00a72). At most 256 KiB. Read strictly: a field not named here is refused.",
+  "type": "object",
+  "additionalProperties": false,
+  "required": [
+    "format",
+    "seat",
+    "scope",
+    "grain",
+    "decision"
+  ],
+  "properties": {
+    "format": {
+      "const": 1
+    },
+    "seat": {
+      "type": "string",
+      "pattern": "^[a-z][a-z0-9-]*[a-z0-9]$"
+    },
+    "scope": {
+      "enum": [
+        "mesh",
+        "node"
+      ]
+    },
+    "grain": {
+      "enum": [
+        "whole",
+        "seat-list"
+      ]
+    },
+    "decision": {
+      "type": "string",
+      "minLength": 1
+    },
+    "description": {
+      "type": "string"
+    },
+    "holder-declares": {
+      "type": "boolean",
+      "description": "the seat is not in the compiled seat list; its holder's manifest declares it"
+    },
+    "delivers": {
+      "type": "string"
+    },
+    "replicated": {
+      "type": "boolean"
+    },
+    "pulled-by-kind": {
+      "type": "boolean"
+    },
+    "yields": {
+      "type": "boolean"
+    },
+    "held-by-the-engine": {
+      "type": "boolean"
+    },
+    "includes": {
+      "type": "array",
+      "items": {
+        "type": "string",
+        "pattern": "^[a-z][a-z0-9-]*$"
+      },
+      "description": "parts/<name>.json taken in whole"
+    },
+    "verbs": {
+      "type": "array",
+      "items": {
+        "$ref": "#/$defs/verb"
+      }
+    },
+    "accepts": {
+      "type": "array",
+      "items": {
+        "$ref": "#/$defs/message"
+      }
+    },
+    "events": {
+      "type": "array",
+      "items": {
+        "$ref": "#/$defs/message"
+      },
+      "description": "published on mesh.seat.<seat>.event.<name>"
+    },
+    "family": {
+      "type": "object",
+      "additionalProperties": false,
+      "required": [
+        "name",
+        "max-age-days"
+      ],
+      "properties": {
+        "name": {
+          "type": "string"
+        },
+        "max-age-days": {
+          "type": "integer",
+          "minimum": 1
+        },
+        "max-mib": {
+          "type": "integer",
+          "minimum": 1
+        }
+      }
+    },
+    "holder-events": {
+      "type": "array",
+      "items": {
+        "type": "object",
+        "additionalProperties": false,
+        "required": [
+          "name",
+          "subject"
+        ],
+        "properties": {
+          "name": {
+            "type": "string",
+            "pattern": "^[a-z][a-z0-9-]*$"
+          },
+          "subject": {
+            "type": "string"
+          },
+          "family": {
+            "type": "string"
+          },
+          "body": {
+            "type": "object",
+            "description": "a JSON Schema"
+          }
+        }
+      },
+      "description": "the holder's own events listed beside the seat, keeping the holder's subjects (ADR 0620 \u00a72)"
+    },
+    "records": {
+      "type": "array",
+      "items": {
+        "type": "object",
+        "additionalProperties": false,
+        "required": [
+          "name"
+        ],
+        "properties": {
+          "name": {
+            "type": "string",
+            "pattern": "^[a-z][a-z0-9-]*$"
+          },
+          "key": {
+            "type": "string"
+          },
+          "value": {
+            "type": "object",
+            "description": "a JSON Schema"
+          }
+        }
+      }
+    },
+    "provisions": {
+      "type": "array",
+      "items": {
+        "type": "object",
+        "additionalProperties": false,
+        "required": [
+          "name",
+          "form"
+        ],
+        "properties": {
+          "name": {
+            "type": "string"
+          },
+          "form": {
+            "type": "object",
+            "description": "a JSON Schema"
+          }
+        }
+      }
+    },
+    "receives": {
+      "type": "array",
+      "items": {
+        "type": "object",
+        "additionalProperties": false,
+        "required": [
+          "kind"
+        ],
+        "properties": {
+          "kind": {
+            "type": "string"
+          },
+          "comment": {
+            "type": "string"
+          },
+          "dirs": {
+            "type": "boolean"
+          },
+          "offered": {
+            "type": "boolean"
+          },
+          "shape": {
+            "type": "object",
+            "additionalProperties": false,
+            "properties": {
+              "places": {
+                "type": "array",
+                "items": {
+                  "type": "object",
+                  "additionalProperties": false,
+                  "required": [
+                    "field"
+                  ],
+                  "properties": {
+                    "field": {
+                      "type": "string"
+                    },
+                    "values": {
+                      "type": "array",
+                      "items": {
+                        "type": "string"
+                      }
+                    }
+                  }
+                }
+              },
+              "order": {
+                "type": "string"
+              },
+              "examples": {
+                "type": "array",
+                "items": {
+                  "type": "object"
+                }
+              },
+              "text": {
+                "type": "boolean"
+              }
+            }
+          }
+        }
+      }
+    },
+    "paths": {
+      "type": "array",
+      "items": {
+        "type": "object",
+        "additionalProperties": false,
+        "required": [
+          "path"
+        ],
+        "properties": {
+          "path": {
+            "type": "string",
+            "pattern": "^/"
+          },
+          "steps-back-for": {
+            "type": "string"
+          }
+        }
+      }
+    },
+    "defs": {
+      "type": "object",
+      "additionalProperties": {
+        "type": "object",
+        "description": "a JSON Schema"
+      }
+    }
+  },
+  "$defs": {
+    "verb": {
+      "type": "object",
+      "additionalProperties": false,
+      "required": [
+        "name"
+      ],
+      "properties": {
+        "name": {
+          "type": "string",
+          "pattern": "^[a-z][a-z0-9-]*$"
+        },
+        "description": {
+          "type": "string"
+        },
+        "optional": {
+          "type": "boolean"
+        },
+        "replaces": {
+          "type": "array",
+          "items": {
+            "type": "string"
+          }
+        },
+        "input": {
+          "type": "object",
+          "description": "a JSON Schema"
+        },
+        "answer": {
+          "type": "object",
+          "description": "a JSON Schema"
+        },
+        "callers": {
+          "type": "string"
+        }
+      }
+    },
+    "message": {
+      "type": "object",
+      "additionalProperties": false,
+      "required": [
+        "name"
+      ],
+      "properties": {
+        "name": {
+          "type": "string",
+          "pattern": "^[a-z][a-z0-9-]*$"
+        },
+        "body": {
+          "type": "object",
+          "description": "a JSON Schema"
+        },
+        "by-caller": {
+          "type": "boolean"
+        }
+      }
+    },
+    "part": {
+      "description": "parts/<name>.json",
+      "type": "object",
+      "additionalProperties": false,
+      "required": [
+        "format",
+        "part"
+      ],
+      "properties": {
+        "format": {
+          "const": 1
+        },
+        "part": {
+          "type": "string",
+          "pattern": "^[a-z][a-z0-9-]*$"
+        },
+        "description": {
+          "type": "string"
+        },
+        "verbs": {
+          "type": "array",
+          "items": {
+            "$ref": "#/$defs/verb"
+          }
+        },
+        "events": {
+          "type": "array",
+          "items": {
+            "$ref": "#/$defs/message"
+          }
+        },
+        "defs": {
+          "type": "object",
+          "additionalProperties": {
+            "type": "object",
+            "description": "a JSON Schema"
+          }
+        }
+      }
+    },
+    "fixtures": {
+      "description": "seats/<seat>/fixtures/*.json: data, never functions",
+      "type": "array",
+      "items": {
+        "type": "object",
+        "additionalProperties": false,
+        "required": [
+          "name",
+          "of",
+          "given"
+        ],
+        "properties": {
+          "name": {
+            "type": "string"
+          },
+          "of": {
+            "type": "string",
+            "pattern": "^(verb:[a-z][a-z0-9-]*\\.(input|answer)|accept:[a-z][a-z0-9-]*|event:[a-z][a-z0-9-]*|holder-event:[a-z][a-z0-9-]*)$"
+          },
+          "subject": {
+            "type": "string"
+          },
+          "given": {},
+          "wire": {},
+          "why": {
+            "type": "string"
+          }
+        }
+      }
+    },
+    "index": {
+      "description": "seats/index.json: the seat list's reading order",
+      "type": "object",
+      "additionalProperties": false,
+      "required": [
+        "format",
+        "seats"
+      ],
+      "properties": {
+        "format": {
+          "const": 1
+        },
+        "seats": {
+          "type": "array",
+          "items": {
+            "type": "string"
+          },
+          "uniqueItems": true
+        }
+      }
+    }
+  }
+}