diff --git a/hack/lib/helm-validation.js b/hack/lib/helm-validation.js
index 3d446fc..83c25e6 100644
--- a/hack/lib/helm-validation.js
+++ b/hack/lib/helm-validation.js
@@ -121,6 +121,10 @@ function parseVersions(file) {
 // (catalogLayer in swiss/internal/compose): its values, with the fields the
 // variant spells first-class projected on top, so they win over the same keys
 // in values. image.digest is not projected.
+//
+// Each declared input is set to its default, else its example, standing in for
+// the answer swiss puts in the derived layer at deploy, so the chart renders
+// every path swiss fills. values never sets one; validate:schema refuses that.
 function catalogValues(variant) {
   const values = structuredClone(variant.values ?? {});
   const set = (keys, value) => {
@@ -136,6 +140,7 @@ function catalogValues(variant) {
     set(["image", "repository"], variant.image.repository);
     set(["image", "tag"], String(variant.image.tag ?? ""));
   }
+  for (const input of variant.inputs ?? []) set(input.key.split("."), "default" in input ? input.default : input.example);
   return values;
 }
 
diff --git a/hack/lib/helm-validation.test.js b/hack/lib/helm-validation.test.js
index ff2abd2..ca08bd3 100644
--- a/hack/lib/helm-validation.test.js
+++ b/hack/lib/helm-validation.test.js
@@ -196,3 +196,20 @@ test("variant values get swiss's projection of servedName, requires.gpus and the
   const [v2] = parseVersions(path.join(dir, "v2.yaml"));
   assert.deepEqual(catalogValues(v2), { model: { name: "served", gpus: "2" } });
 });
+
+test("a declared input renders with its default, else its example", () => {
+  const variant = {
+    servedName: "m",
+    requires: { gpus: 8 },
+    inputs: [
+      { key: "storageKVOffload.mooncake.master", title: "t", example: "mooncake-master.example:50051" },
+      { key: "storageKVOffload.mooncake.device", title: "t", example: "mlx5_0", default: "mlx5_3" },
+    ],
+    values: { storageKVOffload: { enabled: true, mooncake: { protocol: "rdma" } } },
+  };
+  assert.deepEqual(catalogValues(variant).storageKVOffload, {
+    enabled: true,
+    mooncake: { protocol: "rdma", master: "mooncake-master.example:50051", device: "mlx5_3" },
+  });
+  assert.equal(variant.values.storageKVOffload.mooncake.master, undefined);
+});
diff --git a/hack/lib/inputs.js b/hack/lib/inputs.js
new file mode 100644
index 0000000..b3bc384
--- /dev/null
+++ b/hack/lib/inputs.js
@@ -0,0 +1,58 @@
+"use strict";
+// A variant's inputs, past what the schema can see. A key is declared once, and
+// values leaves it alone: swiss puts the answer, the site's or else the input's
+// default, in the derived layer. The example and the default are valid answers.
+// swiss repeats these checks when it loads a variant (internal/catalog).
+
+// Problems with one variant's inputs, each line prefixed with at.
+function inputProblems(variant, at = "") {
+  const inputs = Array.isArray(variant?.inputs) ? variant.inputs : [];
+  const lines = [];
+  const declared = new Set();
+  for (const [i, input] of inputs.entries()) {
+    if (typeof input?.key !== "string") continue; // the schema reports it
+    const where = `${at}inputs[${i}] ${input.key}: `;
+    if (declared.has(input.key)) lines.push(`${where}declared twice`);
+    declared.add(input.key);
+    const set = valueSetAt(variant.values, input.key.split("."));
+    if (set) lines.push(`${where}values.${set} sets it; give the value as the input's default`);
+    const type = input.type ?? "string";
+    let pattern;
+    if (input.pattern !== undefined && type !== "string") {
+      lines.push(`${where}pattern is only for a string input, and this one is ${type}`);
+    } else if (input.pattern !== undefined) {
+      try {
+        pattern = new RegExp(`^(?:${input.pattern})$`, "u");
+      } catch (err) {
+        lines.push(`${where}pattern does not compile: ${err.message}`);
+      }
+    }
+    const answerProblem = (v) => {
+      const ok = type === "integer" ? Number.isInteger(v) : typeof v === type;
+      if (!ok) return `${JSON.stringify(v)} is not ${type === "integer" ? "an" : "a"} ${type}`;
+      if (pattern && !pattern.test(v)) return `${JSON.stringify(v)} does not match the pattern`;
+      return "";
+    };
+    for (const field of ["example", "default"]) {
+      if (!(field in input)) continue;
+      const problem = answerProblem(input[field]);
+      if (problem) lines.push(`${where}${field} ${problem}`);
+    }
+  }
+  return lines;
+}
+
+// The prefix of keys at which values already says something about a dotted
+// key: the value itself, a value under it, or a non-map on the way to it.
+// Empty when values leaves the key alone.
+function valueSetAt(values, keys) {
+  let node = values;
+  for (const [i, key] of keys.entries()) {
+    if (node === null || typeof node !== "object" || Array.isArray(node)) return i > 0 ? keys.slice(0, i).join(".") : "";
+    if (!Object.hasOwn(node, key)) return "";
+    node = node[key];
+  }
+  return keys.join(".");
+}
+
+module.exports = { inputProblems };
diff --git a/hack/lib/inputs.test.js b/hack/lib/inputs.test.js
new file mode 100644
index 0000000..752d1a0
--- /dev/null
+++ b/hack/lib/inputs.test.js
@@ -0,0 +1,62 @@
+"use strict";
+const test = require("node:test");
+const assert = require("node:assert/strict");
+const { inputProblems } = require("./inputs");
+
+const master = {
+  key: "storageKVOffload.mooncake.master",
+  title: "Mooncake master",
+  pattern: "[^\\s:/]+:[0-9]+",
+  example: "mooncake-master.example:50051",
+};
+const variant = (inputs, values = {}) => ({ requires: { gpus: 8 }, inputs, values });
+
+test("a declared input that values leaves alone, with a valid example and default, passes", () => {
+  const values = { storageKVOffload: { enabled: true, mooncake: { protocol: "rdma" } } };
+  assert.deepEqual(inputProblems(variant([master], values)), []);
+  assert.deepEqual(inputProblems(variant([{ ...master, default: "mc:50051" }], values)), []);
+  assert.deepEqual(inputProblems({ requires: { gpus: 1 } }), []);
+});
+
+test("values may not set an input: at its key, under it, or with a non-map on the way", () => {
+  for (const [values, at] of [
+    [{ storageKVOffload: { mooncake: { master: "mc:50051" } } }, "storageKVOffload.mooncake.master"],
+    [{ storageKVOffload: { mooncake: { master: { host: "h" } } } }, "storageKVOffload.mooncake.master"],
+    [{ storageKVOffload: { mooncake: "off" } }, "storageKVOffload.mooncake"],
+  ]) {
+    assert.deepEqual(inputProblems(variant([master], values), "v: "), [
+      `v: inputs[0] storageKVOffload.mooncake.master: values.${at} sets it; give the value as the input's default`,
+    ]);
+  }
+});
+
+test("the default is an answer: of the input's type, matching its pattern", () => {
+  const one = (input) => inputProblems(variant([{ key: "a.b", title: "t", ...input }]));
+  assert.match(one({ example: "h:1", default: "no-port", pattern: master.pattern })[0], /default "no-port" does not match the pattern$/);
+  assert.match(one({ example: "h:1", default: "", pattern: master.pattern })[0], /default "" does not match the pattern$/);
+  assert.match(one({ example: 1, default: "8", type: "integer" })[0], /default "8" is not an integer$/);
+  assert.deepEqual(one({ example: false, default: true, type: "boolean" }), []);
+});
+
+test("a key is declared once", () => {
+  assert.deepEqual(inputProblems(variant([master, master])), ["inputs[1] storageKVOffload.mooncake.master: declared twice"]);
+});
+
+test("the example is an answer: of the input's type, matching its pattern", () => {
+  const one = (input) => inputProblems(variant([{ key: "a.b", title: "t", ...input }]));
+  assert.deepEqual(one({ example: "mooncake-master:50051", pattern: master.pattern }), []);
+  assert.match(one({ example: "no-port", pattern: master.pattern })[0], /example "no-port" does not match the pattern$/);
+  assert.match(one({ example: "8", type: "integer" })[0], /example "8" is not an integer$/);
+  assert.match(one({ example: 1.5, type: "integer" })[0], /is not an integer$/);
+  assert.deepEqual(one({ example: 8, type: "integer" }), []);
+  assert.deepEqual(one({ example: false, type: "boolean" }), []);
+  assert.match(one({ example: 8 })[0], /example 8 is not a string$/);
+});
+
+test("a pattern compiles, and only a string input has one", () => {
+  assert.match(inputProblems(variant([{ ...master, pattern: "(" }]))[0], /pattern does not compile/);
+  assert.match(
+    inputProblems(variant([{ key: "a.b", title: "t", type: "integer", pattern: "[0-9]+", example: 1 }]))[0],
+    /pattern is only for a string input, and this one is integer$/,
+  );
+});
diff --git a/hack/validate-schema.js b/hack/validate-schema.js
index baa6c77..857e5cb 100644
--- a/hack/validate-schema.js
+++ b/hack/validate-schema.js
@@ -27,6 +27,7 @@ const {
   checkIndexV2,
 } = require("./lib/catalog");
 const { reportProblem } = require("./lib/report");
+const { inputProblems } = require("./lib/inputs");
 const { paint, marks, plural } = require("./lib/style");
 
 const {
@@ -225,6 +226,7 @@ function variantProblems(v, at) {
       if (v.requires[key] !== undefined) lines.push(`${at}requires.${key} is set, but requires.gpus 0 is CPU only`);
     }
   }
+  lines.push(...inputProblems(v, at));
   return lines;
 }
 
diff --git a/schema/variant.schema.json b/schema/variant.schema.json
index 44d9f53..dd9d5f7 100644
--- a/schema/variant.schema.json
+++ b/schema/variant.schema.json
@@ -48,6 +48,9 @@
     "requires": {
       "$ref": "version.schema.json#/$defs/variant/properties/requires"
     },
+    "inputs": {
+      "$ref": "version.schema.json#/$defs/variant/properties/inputs"
+    },
     "values": {
       "$ref": "version.schema.json#/$defs/variant/properties/values"
     },
diff --git a/schema/version.schema.json b/schema/version.schema.json
index ee2bb9c..92980b2 100644
--- a/schema/version.schema.json
+++ b/schema/version.schema.json
@@ -168,6 +168,52 @@
             }
           ]
         },
+        "inputs": {
+          "description": "Chart values every deploy must answer, such as the address of a service the site runs. Unlike requires, which swiss interprets and checks against the cluster, an input names one chart value by its key, and swiss only relays its answer: swiss puts the answer in the derived layer -- the site profile's inputs, else the input's default -- and the deploy's overrides go over it. swiss refuses to compose a plan that leaves one without a valid answer. values never sets an input's key. model.localPath is never one: swiss answers it from the site's model.pathTemplate.",
+          "type": "array",
+          "minItems": 1,
+          "items": {
+            "type": "object",
+            "additionalProperties": false,
+            "required": ["key", "title", "example"],
+            "properties": {
+              "key": {
+                "description": "The chart value's dotted key, as helm --set takes it: storageKVOffload.mooncake.master. Unique within the variant.",
+                "type": "string",
+                "pattern": "^[A-Za-z_][A-Za-z0-9_-]*(\\.[A-Za-z_][A-Za-z0-9_-]*)*$",
+                "not": { "enum": ["model.localPath"] }
+              },
+              "title": {
+                "description": "What the deploy form labels the field with.",
+                "type": "string",
+                "minLength": 1
+              },
+              "description": {
+                "description": "What the value is, for the deploy form.",
+                "type": "string",
+                "minLength": 1
+              },
+              "type": {
+                "description": "What an answer is.",
+                "enum": ["string", "integer", "boolean"],
+                "default": "string"
+              },
+              "pattern": {
+                "description": "A regular expression a string answer matches, whole. Keep to the syntax Go and JavaScript read alike: swiss checks it, and so does the deploy form.",
+                "type": "string",
+                "minLength": 1
+              },
+              "example": {
+                "description": "A value of the right shape, never a real one: the deploy form's placeholder, and what CI renders the chart with when there is no default. Never deployed. Must be of the input's type and match its pattern.",
+                "type": ["string", "integer", "boolean"]
+              },
+              "default": {
+                "description": "The answer when the site profile gives none, such as the value of the cluster the variant was tuned on. Must be of the input's type and match its pattern.",
+                "type": ["string", "integer", "boolean"]
+              }
+            }
+          }
+        },
         "values": {
           "description": "Chart values this variant sets. Any object",
           "type": "object"