diff --git a/javascript/packages/analysis/src/dependency-index.ts b/javascript/packages/analysis/src/dependency-index.ts
new file mode 100644
index 000000000..fbce25a61
--- /dev/null
+++ b/javascript/packages/analysis/src/dependency-index.ts
@@ -0,0 +1,141 @@
+import { collectTemplateDependencies } from "./template-dependencies"
+import { isERBCaseNode, isERBContentNode, isERBIfNode, isERBRenderNode, isERBUnlessNode, isHTMLAttributeNode, isLiteralNode } from "@herb-tools/core"
+
+const PARSER_OPTIONS = { render_nodes: true, strict_locals: true, prism_nodes: true, prism_program: true, track_whitespace: true }
+
+import type { DependencyOptions } from "./template-dependencies"
+import type { DocumentNode, HTMLAttributeNode, HerbBackend, Node, Token } from "@herb-tools/core"
+
+export type AffectedNodeKind = "text_content" | "conditional" | "render" | "attribute_value"
+
+export interface AffectedNode {
+  nodePath: number[]
+  kind: AffectedNodeKind
+  expression?: string
+  attribute?: string
+  location?: string
+}
+
+export function referencesState(code: string | undefined, state: string): boolean {
+  if (!code || !state) return false
+
+  if (state.startsWith("@")) {
+    return code.includes(state)
+  }
+
+  if (state.includes(".")) {
+    return code.includes(state.split(".")[0])
+  }
+
+  return new RegExp(`\\b${state.replace(/[.*+?^${}()|[\]\\]/g, "\\$&")}\\b`).test(code)
+}
+
+function childrenOf(node: Node): Node[] {
+  return node.childNodes().filter((child): child is Node => child !== null)
+}
+
+function locationOf(node: Node): string | undefined {
+  const start = node.location?.start
+
+  return start ? `${start.line}:${start.column}` : undefined
+}
+
+function expressionOf(node: Node): string | undefined {
+  const value = "content" in node ? (node as { content?: Token | null }).content?.value : undefined
+
+  return typeof value === "string" ? value.trim() : undefined
+}
+
+function expressionsWithin(node: Node): string[] {
+  const own = expressionOf(node)
+  const found = own ? [own] : []
+
+  for (const child of childrenOf(node)) found.push(...expressionsWithin(child))
+
+  return found
+}
+
+function attributeNameOf(node: HTMLAttributeNode): string | undefined {
+  const [first] = node.name?.children ?? []
+  const literal = first && isLiteralNode(first) ? first.content : undefined
+
+  return typeof literal === "string" ? literal : undefined
+}
+
+export function affectedNodes(backend: HerbBackend, source: string, state: string): AffectedNode[] {
+  const document = backend.parse(source, PARSER_OPTIONS).value as DocumentNode
+  const affected: AffectedNode[] = []
+  const path: number[] = []
+
+  const record = (node: Node, kind: AffectedNodeKind, expression?: string) => {
+    affected.push({
+      nodePath: [...path],
+      kind,
+      ...(expression ? { expression } : {}),
+      ...(locationOf(node) ? { location: locationOf(node) } : {}),
+    })
+  }
+
+  const inspectAttribute = (node: HTMLAttributeNode) => {
+    const attribute = attributeNameOf(node)
+
+    for (const value of node.value?.children ?? []) {
+      const expression = expressionOf(value)
+
+      if (!referencesState(expression, state)) continue
+
+      affected.push({
+        nodePath: [...path],
+        kind: "attribute_value",
+        ...(expression ? { expression } : {}),
+        ...(attribute ? { attribute } : {}),
+        ...(locationOf(value) ? { location: locationOf(value) } : {}),
+      })
+    }
+  }
+
+  const walk = (node: Node) => {
+    if (isHTMLAttributeNode(node)) {
+      inspectAttribute(node)
+
+      return
+    }
+
+    if (isERBIfNode(node) || isERBUnlessNode(node) || isERBCaseNode(node)) {
+      if (expressionsWithin(node).some(code => referencesState(code, state))) {
+        record(node, "conditional", expressionOf(node))
+      }
+    } else if (isERBContentNode(node) && referencesState(expressionOf(node), state)) {
+      record(node, "text_content", expressionOf(node))
+    } else if (isERBRenderNode(node) && referencesState(expressionOf(node), state)) {
+      record(node, "render", expressionOf(node))
+    }
+
+    for (const [index, child] of childrenOf(node).entries()) {
+      path.push(index)
+      walk(child)
+      path.pop()
+    }
+  }
+
+  for (const [index, child] of childrenOf(document).entries()) {
+    path.push(index)
+    walk(child)
+    path.pop()
+  }
+
+  return affected
+}
+
+export function dependencyIndex(backend: HerbBackend, file: string, source: string, options: DependencyOptions = {}): Record<string, AffectedNode[]> {
+  const dependencies = collectTemplateDependencies(backend, file, source, options)
+  const index: Record<string, AffectedNode[]> = {}
+
+  for (const state of [...dependencies.instanceVariables, ...dependencies.constants]) {
+    const nodes = affectedNodes(backend, source, state)
+
+    if (nodes.length > 0) index[state] = nodes
+  }
+
+  return index
+}
diff --git a/javascript/packages/analysis/src/index.ts b/javascript/packages/analysis/src/index.ts
index 118b7941f..f60551ca2 100644
--- a/javascript/packages/analysis/src/index.ts
+++ b/javascript/packages/analysis/src/index.ts
@@ -1,5 +1,6 @@
 export * from "./affected-templates"
 export * from "./ancestor-attributes"
+export * from "./dependency-index"
 export * from "./partial-callers"
 export * from "./partial-index"
 export * from "./partial-resolution"
diff --git a/javascript/packages/analysis/test/dependency-index.test.ts b/javascript/packages/analysis/test/dependency-index.test.ts
new file mode 100644
index 000000000..3edb35bc0
--- /dev/null
+++ b/javascript/packages/analysis/test/dependency-index.test.ts
@@ -0,0 +1,102 @@
+import { describe, test, expect, beforeAll } from "vitest"
+
+import { Herb } from "@herb-tools/node-wasm"
+
+import { affectedNodes, dependencyIndex, referencesState } from "../src/dependency-index"
+
+const FILE = "app/views/posts/show.html.erb"
+
+describe("dependencyIndex", () => {
+  beforeAll(async () => {
+    await Herb.load()
+  })
+
+  function indexOf(source: string) {
+    return dependencyIndex(Herb, FILE, source)
+  }
+
+  test("maps state to the nodes that read it", () => {
+    const index = indexOf(`<div><h1><%= @post.title %></h1><p><%= @post.body %></p></div>`)
+
+    expect(index["@post"]).toBeDefined()
+    expect(index["@post"]).toHaveLength(2)
+    expect(index["@post"].map(node => node.kind)).toEqual(["text_content", "text_content"])
+  })
+
+  test("includes attribute values", () => {
+    const index = indexOf(`<div class="<%= @active ? "on" : "off" %>">Content</div>`)
+
+    expect(index["@active"]).toBeDefined()
+
+    const attribute = index["@active"].find(node => node.kind === "attribute_value")
+
+    expect(attribute).toBeDefined()
+    expect(attribute?.attribute).toBe("class")
+  })
+
+  test("marks an if block containing state as conditional", () => {
+    const index = indexOf(`<div><% if @admin %><%= @post.name %><% end %></div>`)
+
+    expect(index["@post"].map(node => node.kind)).toEqual(expect.arrayContaining(["conditional", "text_content"]))
+    expect(index["@admin"][0].kind).toBe("conditional")
+  })
+
+  test("leaves out state that nothing reads", () => {
+    expect(indexOf(`<h1>Static</h1>`)).toEqual({})
+  })
+
+  test("records where each node is", () => {
+    const [node] = indexOf(`<div><h1><%= @post.title %></h1></div>`)["@post"]
+
+    expect(node.location).toMatch(/^\d+:\d+$/)
+    expect(node.expression).toBe("@post.title")
+  })
+
+  test("records a path that leads back to the node", () => {
+    const [node] = indexOf(`<div><h1><%= @post.title %></h1></div>`)["@post"]
+
+    expect(node.nodePath.length).toBeGreaterThan(0)
+    expect(node.nodePath.every(step => Number.isInteger(step))).toBe(true)
+  })
+
+  test("covers constants as well as instance variables", () => {
+    const index = indexOf(`<%= Post.count %>`)
+
+    expect(index["Post.count"]).toBeDefined()
+    expect(index["Post.count"][0].kind).toBe("text_content")
+  })
+
+  describe("affectedNodes", () => {
+    test("finds nothing for state the template does not read", () => {
+      expect(affectedNodes(Herb, `<%= @post.title %>`, "@other")).toEqual([])
+    })
+
+    test("finds a render call that passes the state on", () => {
+      const nodes = affectedNodes(Herb, `<%= render "posts/card", post: @post %>`, "@post")
+
+      expect(nodes.some(node => node.kind === "render")).toBe(true)
+    })
+  })
+
+  describe("referencesState", () => {
+    test("matches an instance variable literally", () => {
+      expect(referencesState("@post.title", "@post")).toBe(true)
+      expect(referencesState("@other.title", "@post")).toBe(false)
+    })
+
+    test("matches a constant on the constant alone", () => {
+      expect(referencesState("Post.where(id: 1)", "Post.count")).toBe(true)
+      expect(referencesState("Comment.count", "Post.count")).toBe(false)
+    })
+
+    test("matches a plain name on word boundaries", () => {
+      expect(referencesState("post.title", "post")).toBe(true)
+      expect(referencesState("posts.count", "post")).toBe(false)
+    })
+
+    test("is false for nothing", () => {
+      expect(referencesState(undefined, "@post")).toBe(false)
+      expect(referencesState("@post", "")).toBe(false)
+    })
+  })
+})