diff --git a/bun.lock b/bun.lock
index 798170796..04be30353 100644
--- a/bun.lock
+++ b/bun.lock
@@ -108,6 +108,14 @@
         "@oh-my-opencode/utils": "workspace:*",
       },
     },
+    "packages/prompts-core": {
+      "name": "@oh-my-opencode/prompts-core",
+      "version": "0.1.0",
+      "peerDependencies": {
+        "@oh-my-opencode/model-core": "workspace:*",
+        "@oh-my-opencode/utils": "workspace:*",
+      },
+    },
     "packages/rules-engine": {
       "name": "@oh-my-opencode/rules-engine",
       "version": "0.1.0",
@@ -209,6 +217,8 @@
 
     "@oh-my-opencode/model-core": ["@oh-my-opencode/model-core@workspace:packages/model-core"],
 
+    "@oh-my-opencode/prompts-core": ["@oh-my-opencode/prompts-core@workspace:packages/prompts-core"],
+
     "@oh-my-opencode/rules-engine": ["@oh-my-opencode/rules-engine@workspace:packages/rules-engine"],
 
     "@oh-my-opencode/utils": ["@oh-my-opencode/utils@workspace:packages/utils"],
diff --git a/package.json b/package.json
index 873783204..b42a560fe 100644
--- a/package.json
+++ b/package.json
@@ -11,6 +11,7 @@
     "packages/ast-grep-mcp",
     "packages/utils",
     "packages/model-core",
+    "packages/prompts-core",
     "packages/comment-checker-core",
     "packages/hashline-core",
     "packages/boulder-state",
diff --git a/packages/prompts-core/package.json b/packages/prompts-core/package.json
new file mode 100644
index 000000000..73c10187e
--- /dev/null
+++ b/packages/prompts-core/package.json
@@ -0,0 +1,22 @@
+{
+  "name": "@oh-my-opencode/prompts-core",
+  "version": "0.1.0",
+  "type": "module",
+  "private": true,
+  "description": "Harness-agnostic markdown prompt loading and model-variant routing for oh-my-opencode.",
+  "exports": {
+    ".": {
+      "types": "./index.d.ts",
+      "import": "./src/index.ts"
+    }
+  },
+  "types": "./index.d.ts",
+  "scripts": {
+    "typecheck": "tsgo --noEmit -p tsconfig.json",
+    "test": "bun test src/*.test.ts test/*.test.ts"
+  },
+  "peerDependencies": {
+    "@oh-my-opencode/model-core": "workspace:*",
+    "@oh-my-opencode/utils": "workspace:*"
+  }
+}
diff --git a/packages/prompts-core/src/index.ts b/packages/prompts-core/src/index.ts
new file mode 100644
index 000000000..f12a83c8b
--- /dev/null
+++ b/packages/prompts-core/src/index.ts
@@ -0,0 +1,8 @@
+export type {
+  LoadedPrompt,
+  LoadPromptInput,
+  ModelVariant,
+  PromptSource,
+  RuntimeInjection,
+  VariantTable,
+} from "./types"
diff --git a/packages/prompts-core/src/types.test.ts b/packages/prompts-core/src/types.test.ts
new file mode 100644
index 000000000..50b1a4b47
--- /dev/null
+++ b/packages/prompts-core/src/types.test.ts
@@ -0,0 +1,32 @@
+import { describe, expect, test } from "bun:test"
+import type { LoadPromptInput, LoadedPrompt, PromptSource, RuntimeInjection } from "./types"
+
+describe("prompt core types", () => {
+  test("#given loader input shape #then accepts source name variant and runtime injections", () => {
+    const source: PromptSource = { baseDir: "/tmp/prompts" }
+    const injection: RuntimeInjection = { placeholder: "{X}", resolver: () => "Y" }
+
+    const input = {
+      source,
+      name: "test",
+      variant: "default",
+      inject: [injection],
+    } satisfies LoadPromptInput
+
+    expect(input.source.baseDir).toBe("/tmp/prompts")
+    expect(input.inject[0]?.placeholder).toBe("{X}")
+  })
+
+  test("#given loaded prompt shape #then carries frontmatter and rendered body", () => {
+    const loaded = {
+      frontmatter: { title: "Fixture" },
+      body: "Prompt body",
+      hadFrontmatter: true,
+      parseError: false,
+      filePath: "/tmp/prompts/test/default.md",
+    } satisfies LoadedPrompt<{ readonly title: string }>
+
+    expect(loaded.frontmatter.title).toBe("Fixture")
+    expect(loaded.body).toBe("Prompt body")
+  })
+})
diff --git a/packages/prompts-core/src/types.ts b/packages/prompts-core/src/types.ts
new file mode 100644
index 000000000..c70351455
--- /dev/null
+++ b/packages/prompts-core/src/types.ts
@@ -0,0 +1,35 @@
+export type ModelVariant =
+  | "default"
+  | "gpt"
+  | "gemini"
+  | "kimi"
+  | "glm"
+  | "planner"
+  | "opus-4-7"
+  | "minimax"
+
+export type PromptSource = {
+  readonly baseDir: string
+}
+
+export type RuntimeInjection = {
+  readonly placeholder: string
+  readonly resolver: () => string | Promise<string>
+}
+
+export type LoadPromptInput = {
+  readonly source: PromptSource
+  readonly name: string
+  readonly variant: string
+  readonly inject?: readonly RuntimeInjection[]
+}
+
+export type LoadedPrompt<TFrontmatter = Record<string, unknown>> = {
+  readonly frontmatter: TFrontmatter
+  readonly body: string
+  readonly hadFrontmatter: boolean
+  readonly parseError: boolean
+  readonly filePath: string
+}
+
+export type VariantTable = Readonly<Record<string, PromptSource>>
diff --git a/packages/prompts-core/tsconfig.json b/packages/prompts-core/tsconfig.json
new file mode 100644
index 000000000..6a768d440
--- /dev/null
+++ b/packages/prompts-core/tsconfig.json
@@ -0,0 +1,14 @@
+{
+  "compilerOptions": {
+    "target": "ESNext",
+    "module": "ESNext",
+    "moduleResolution": "bundler",
+    "strict": true,
+    "esModuleInterop": true,
+    "skipLibCheck": true,
+    "forceConsistentCasingInFileNames": true,
+    "lib": ["ESNext"],
+    "types": ["bun-types"]
+  },
+  "include": ["src/**/*", "test/**/*"]
+}