diff --git a/openspec/README.md b/openspec/README.md
index 81a58328..a9d0cafe 100644
--- a/openspec/README.md
+++ b/openspec/README.md
@@ -87,6 +87,7 @@ After deployment, create separate PR to:
 openspec list                  # List active changes
 openspec list --specs          # List specifications
 openspec show [item]           # Display change or spec
+openspec diff [change]         # Show spec differences
 openspec validate [item]       # Validate changes or specs
 openspec archive [change]      # Archive after deployment
 
@@ -255,6 +256,19 @@ Every requirement MUST have at least one scenario.
 
 Headers matched with `trim(header)` - whitespace ignored.
 
+#### When to use ADDED vs MODIFIED
+- ADDED: Introduces a new capability or sub-capability that can stand alone as a requirement. Prefer ADDED when the change is orthogonal (e.g., adding "Slash Command Configuration") rather than altering the semantics of an existing requirement.
+- MODIFIED: Changes the behavior, scope, or acceptance criteria of an existing requirement. Always paste the full, updated requirement content (header + all scenarios). The archiver will replace the entire requirement with what you provide here; partial deltas will drop previous details.
+- RENAMED: Use when only the name changes. If you also change behavior, use RENAMED (name) plus MODIFIED (content) referencing the new name.
+
+Common pitfall: Using MODIFIED to add a new concern without including the previous text. This causes loss of detail at archive time. If you aren’t explicitly changing the existing requirement, add a new requirement under ADDED instead.
+
+Authoring a MODIFIED requirement correctly:
+1) Locate the existing requirement in `openspec/specs/<capability>/spec.md`.
+2) Copy the entire requirement block (from `### Requirement: ...` through its scenarios).
+3) Paste it under `## MODIFIED Requirements` and edit to reflect the new behavior.
+4) Ensure the header text matches exactly (whitespace-insensitive) and keep at least one `#### Scenario:`.
+
 Example for RENAMED:
 ```markdown
 ## RENAMED Requirements
@@ -425,6 +439,7 @@ Only add complexity with:
 ```bash
 openspec list              # What's in progress?
 openspec show [item]       # View details
+openspec diff [change]     # What's changing?
 openspec validate --strict # Is it correct?
 openspec archive [change]  # Mark complete
 ```
diff --git a/openspec/changes/add-slash-command-support/proposal.md b/openspec/changes/add-slash-command-support/proposal.md
new file mode 100644
index 00000000..f11413a1
--- /dev/null
+++ b/openspec/changes/add-slash-command-support/proposal.md
@@ -0,0 +1,119 @@
+# Add Slash Command Support for Coding Agents
+
+## Summary
+- Enable OpenSpec to generate and update custom slash commands for supported coding agents (Claude Code and Cursor).
+- Provide three slash commands aligned with OpenSpec's workflow: proposal (start a change proposal), apply (implement), and archive.
+- Share slash command templating between agents to make future extensions simple.
+
+## Motivation
+Developers use different coding agents and editors. Having consistent slash commands across tools for the OpenSpec workflow reduces friction and ensures a standard way to trigger the workflow. Supporting both Claude Code and Cursor now lays a foundation for future agents that introduce slash command features.
+
+## Proposal
+1. During `openspec init`, when a user selects a supported tool, generate slash command configuration for three OpenSpec workflow stages:
+   - Claude (namespaced): `/openspec/proposal`, `/openspec/apply`, `/openspec/archive`.
+   - Cursor (flat, prefixed): `/openspec-proposal`, `/openspec-apply`, `/openspec-archive`.
+   - Semantics:
+     - Create – scaffold a change (ID, `proposal.md`, `tasks.md`, delta specs); validate strictly.
+     - Apply – implement an approved change; complete tasks; validate strictly.
+     - Archive – archive after deployment; update specs if needed.
+   - Each command file MUST embed concise, step-by-step instructions sourced from `openspec/README.md` (see Template Content section).
+2. Store slash command files per tool:
+   - Claude Code: `.claude/commands/openspec/{proposal,apply,archive}.md`
+   - Cursor: `.cursor/commands/{openspec-proposal,openspec-apply,openspec-archive}.md`
+   - Ensure nested directories are created.
+3. Command file format and metadata:
+   - Use Markdown with optional YAML frontmatter for tool metadata (name/title, description, category/tags) when supported by the tool.
+   - Place OpenSpec markers around the body only, never inside frontmatter.
+   - Keep the visible slash name, file name, and any frontmatter `name`/`id` consistently aligned (e.g., `proposal`, `openspec-proposal`).
+   - Namespacing: categorize these under “OpenSpec” and prefer unique IDs (e.g., `openspec-proposal`) to avoid collisions.
+4. Centralize templates: define command bodies once and reuse across tools; apply minimal per-tool wrappers (frontmatter, categories, filenames).
+5. During `openspec update`, refresh only existing slash command files (per-file basis) within markers; do not create missing files or new tools.
+
+## Design Ideas
+- Introduce `SlashCommandConfigurator` to manage multiple files per tool.
+  - Expose targets rather than a single `configFileName` (e.g., `getTargets(): Array<{ path: string; kind: 'slash'; id: string }>`).
+  - Provide `generateAll(projectPath, openspecDir)` for init and `updateExisting(projectPath, openspecDir)` for update.
+- Per-tool adapters add only frontmatter and pathing; bodies come from shared templates.
+- Templates live in `TemplateManager` with helpers that extract concise, authoritative snippets from `openspec/README.md`.
+- Update flow logs per-file results so users see exactly which slash files were refreshed.
+
+### Marker Placement
+- Markers MUST wrap only the Markdown body contents:
+  - Frontmatter (if present) goes first.
+  - Then `<!-- OPENSPEC:START -->` … body … `<!-- OPENSPEC:END -->`.
+  - Avoid inserting markers into the YAML block to prevent parse errors.
+
+### Idempotency and Creation Rules
+- `init`: create all three files for the chosen tool(s) once; subsequent `init` runs are no-ops for existing files.
+- `update`: refresh only files that exist; skip missing ones without creating new files.
+- Directory creation for `.claude/commands/openspec/` and `.cursor/commands/` is the configurator’s responsibility.
+
+### Command Naming & UX
+- Claude Code: use namespacing in the slash itself for readability and grouping: `/openspec/proposal`, `/openspec/apply`, `/openspec/archive`.
+- Cursor: use flat names with an `openspec-` prefix: `/openspec-proposal`, `/openspec-apply`, `/openspec-archive`. Group via `category: OpenSpec` when supported.
+- Consistency: align file names, visible slash names, and any frontmatter `id` (e.g., `id: openspec-apply`).
+- Migration: do not rename existing commands during `update`; apply new naming only on `init` (or via an explicit migrate step).
+
+## Open Questions
+- Validate exact metadata/frontmatter supported by each tool version; if unsupported, omit frontmatter and ship Markdown body only.
+- Confirm the final Cursor command file location for the targeted versions; fall back to Markdown-only if Cursor does not parse frontmatter.
+- Evaluate additional commands beyond the initial three (e.g., `/show-change`, `/validate-all`) based on user demand.
+
+## Alternatives
+- Hard-code slash command text per tool (rejected: duplicates content; increases maintenance).
+- Delay Cursor support until its config stabilizes (partial accept): gate Cursor behind a feature flag until verified in real environments.
+
+## Risks
+- Tool configuration formats may change, requiring updates to wrappers/frontmatter.
+- Incorrect paths or categories can hide commands; add path existence checks and clear logging.
+- Marker misuse (inside frontmatter) can break parsing; enforce placement rules in tests.
+
+## Future Work
+- Support additional editors/agents that expose slash command APIs.
+- Allow users to customize command names and categories during `openspec init`.
+- Provide a dedicated command to regenerate slash commands without running full `update`.
+
+## File Format Examples
+The following examples illustrate expected structure. If a tool does not support frontmatter, omit the YAML block and keep only the markers + body.
+
+### Claude Code: `.claude/commands/openspec/proposal.md`
+```markdown
+---
+name: OpenSpec: Proposal
+description: Scaffold a new OpenSpec change and validate strictly.
+category: OpenSpec
+tags: [openspec, change]
+---
+<!-- OPENSPEC:START -->
+...command body from shared template...
+<!-- OPENSPEC:END -->
+```
+
+Slash invocation: `/openspec/proposal` (namespaced)
+
+### Cursor: `.cursor/commands/openspec-proposal.md`
+```markdown
+---
+name: /openspec-proposal
+id: openspec-proposal
+category: OpenSpec
+description: Scaffold a new OpenSpec change and validate strictly.
+---
+<!-- OPENSPEC:START -->
+...command body from shared template...
+<!-- OPENSPEC:END -->
+```
+
+Slash invocation: `/openspec-proposal` (flat, prefixed)
+
+## Template Content
+Templates should be brief, actionable, and sourced from `openspec/README.md` to avoid duplication. Each command body includes:
+- Guardrails: ask 1–2 clarifying questions if needed; follow minimal-complexity rules; use `pnpm` for Node projects.
+- Step list tailored to the workflow stage (proposal, apply, archive), including strict validation commands.
+- Pointers to `openspec show`, `openspec list`, and troubleshooting tips when validation fails.
+
+## Testing Strategy
+- Golden snapshots for generated files per tool (frontmatter + markers + body).
+- Partial presence tests: if 1–2 files exist, `update` only refreshes those and does not create missing ones.
+- Marker placement tests: ensure markers never appear inside frontmatter; cover missing/duplicated marker recovery behavior.
+- Logging tests: `update` reports per-file updates for slash commands.
diff --git a/openspec/changes/add-slash-command-support/specs/cli-init/spec.md b/openspec/changes/add-slash-command-support/specs/cli-init/spec.md
new file mode 100644
index 00000000..afa057f2
--- /dev/null
+++ b/openspec/changes/add-slash-command-support/specs/cli-init/spec.md
@@ -0,0 +1,15 @@
+## ADDED Requirements
+### Requirement: Slash Command Configuration
+The init command SHALL generate slash command files for supported editors using shared templates.
+
+#### Scenario: Generating slash commands for Claude Code
+- **WHEN** the user selects Claude Code during initialization
+- **THEN** create `.claude/commands/openspec/proposal.md`, `.claude/commands/openspec/apply.md`, and `.claude/commands/openspec/archive.md`
+- **AND** populate each file from shared templates so command text matches other tools
+- **AND** each template includes instructions for the relevant OpenSpec workflow stage
+
+#### Scenario: Generating slash commands for Cursor
+- **WHEN** the user selects Cursor during initialization
+- **THEN** create `.cursor/commands/openspec-proposal.md`, `.cursor/commands/openspec-apply.md`, and `.cursor/commands/openspec-archive.md`
+- **AND** populate each file from shared templates so command text matches other tools
+- **AND** each template includes instructions for the relevant OpenSpec workflow stage
diff --git a/openspec/changes/add-slash-command-support/specs/cli-update/spec.md b/openspec/changes/add-slash-command-support/specs/cli-update/spec.md
new file mode 100644
index 00000000..03f054bc
--- /dev/null
+++ b/openspec/changes/add-slash-command-support/specs/cli-update/spec.md
@@ -0,0 +1,17 @@
+## ADDED Requirements
+### Requirement: Slash Command Updates
+The update command SHALL refresh existing slash command files for configured tools without creating new ones.
+
+#### Scenario: Updating slash commands for Claude Code
+- **WHEN** `.claude/commands/openspec/` contains `proposal.md`, `apply.md`, and `archive.md`
+- **THEN** refresh each file using shared templates
+- **AND** ensure templates include instructions for the relevant workflow stage
+
+#### Scenario: Updating slash commands for Cursor
+- **WHEN** `.cursor/commands/` contains `openspec-proposal.md`, `openspec-apply.md`, and `openspec-archive.md`
+- **THEN** refresh each file using shared templates
+- **AND** ensure templates include instructions for the relevant workflow stage
+
+#### Scenario: Missing slash command file
+- **WHEN** a tool lacks a slash command file
+- **THEN** do not create a new file during update
diff --git a/openspec/changes/add-slash-command-support/tasks.md b/openspec/changes/add-slash-command-support/tasks.md
new file mode 100644
index 00000000..cb194c04
--- /dev/null
+++ b/openspec/changes/add-slash-command-support/tasks.md
@@ -0,0 +1,16 @@
+# Implementation Tasks
+
+## 1. Templates and Configurators
+- [ ] 1.1 Create shared templates for the Proposal, Apply, and Archive commands with instructions for each workflow stage from `openspec/README.md`.
+- [ ] 1.2 Implement a `SlashCommandConfigurator` base and tool-specific configurators for Claude Code and Cursor.
+
+## 2. Claude Code Integration
+- [ ] 2.1 Generate `.claude/commands/openspec/{proposal,apply,archive}.md` during `openspec init` using shared templates.
+- [ ] 2.2 Update existing `.claude/commands/openspec/*` files during `openspec update`.
+
+## 3. Cursor Integration
+- [ ] 3.1 Generate `.cursor/commands/{openspec-proposal,openspec-apply,openspec-archive}.md` during `openspec init` using shared templates.
+- [ ] 3.2 Update existing `.cursor/commands/*` files during `openspec update`.
+
+## 4. Verification
+- [ ] 4.1 Add tests verifying slash command files are created and updated correctly.
diff --git a/openspec/changes/make-validation-scope-aware/proposal.md b/openspec/changes/make-validation-scope-aware/proposal.md
new file mode 100644
index 00000000..391b703c
--- /dev/null
+++ b/openspec/changes/make-validation-scope-aware/proposal.md
@@ -0,0 +1,12 @@
+## Why
+Validation currently errors on changes without spec deltas, even when the change is intentionally proposal-only or tooling-only. This creates false negatives and noisy CI.
+
+## What Changes
+- Make change validation scope-aware: validate only artifacts that exist.
+- Only error on "No deltas found" if spec delta files exist but parse to zero deltas.
+- Keep archive stricter: if specs exist but parse to zero deltas, fail; allow `--skip-specs` for tooling-only changes.
+
+## Impact
+- Affected specs: cli-validate
+- Affected code: `src/commands/validate.ts`, `src/core/validation/validator.ts`
+
diff --git a/openspec/changes/make-validation-scope-aware/specs/cli-validate/spec.md b/openspec/changes/make-validation-scope-aware/specs/cli-validate/spec.md
new file mode 100644
index 00000000..cae28c91
--- /dev/null
+++ b/openspec/changes/make-validation-scope-aware/specs/cli-validate/spec.md
@@ -0,0 +1,25 @@
+## ADDED Requirements
+### Requirement: Scope-Aware Change Validation
+The validator SHALL validate only artifacts that exist for a change, avoiding errors for proposal-only or tooling-only changes.
+
+#### Scenario: Proposal-only change
+- **WHEN** a change contains `proposal.md` but has no `specs/` directory or contains no `*/spec.md` files
+- **THEN** validate the proposal (Why/What sections)
+- **AND** do not require or validate spec deltas
+
+#### Scenario: Delta validation when specs exist
+- **WHEN** a change contains one or more `specs/<capability>/spec.md` files
+- **THEN** validate delta-formatted specs with existing rules (SHALL/MUST, scenarios, duplicates, conflicts)
+
+## MODIFIED Requirements
+### Requirement: Validation SHALL provide actionable remediation steps
+Validation output SHALL include specific guidance to fix each error, including expected structure, example headers, and suggested commands to verify fixes.
+
+#### Scenario: No deltas found in change
+- **WHEN** validating a change that contains `specs/` with one or more `*/spec.md` files but the parser finds zero deltas
+- **THEN** show error "No deltas found" with guidance:
+  - Ensure `openspec/changes/{id}/specs/` has `.md` files that include delta headers
+  - Use delta headers: `## ADDED Requirements`, `## MODIFIED Requirements`, `## REMOVED Requirements`, `## RENAMED Requirements`
+  - Each requirement must include at least one `#### Scenario:` block
+  - Try: `openspec change show {id} --json --deltas-only` to inspect parsed deltas
+
diff --git a/openspec/changes/make-validation-scope-aware/tasks.md b/openspec/changes/make-validation-scope-aware/tasks.md
new file mode 100644
index 00000000..9ccf3906
--- /dev/null
+++ b/openspec/changes/make-validation-scope-aware/tasks.md
@@ -0,0 +1,16 @@
+## 1. Validator changes
+- [ ] 1.1 Change `validateChangeDeltaSpecs` to only emit "Change must have at least one delta" when `specs/` exists and contains at least one `*/spec.md` but parsed total deltas is 0
+- [ ] 1.2 Return valid (no error) when `specs/` directory is missing or has no `spec.md` files
+
+## 2. CLI changes
+- [ ] 2.1 In bulk validation, keep current behavior (call delta validator). Behavior remains correct after 1.1
+- [ ] 2.2 Add a short INFO log in human-readable mode when a change has no `specs/` (optional)
+
+## 3. Documentation
+- [ ] 3.1 Update README and template: "Validation checks only existing artifacts. Proposal-only changes are valid without spec deltas."
+
+## 4. Tests
+- [ ] 4.1 Add test: proposal-only change passes validation without deltas
+- [ ] 4.2 Add test: specs present but zero parsed deltas → ERROR
+- [ ] 4.3 Add test: specs present with proper deltas → valid
+
diff --git a/src/core/templates/readme-template.ts b/src/core/templates/readme-template.ts
index 4e5cbd23..aa78424d 100644
--- a/src/core/templates/readme-template.ts
+++ b/src/core/templates/readme-template.ts
@@ -256,6 +256,19 @@ Every requirement MUST have at least one scenario.
 
 Headers matched with \`trim(header)\` - whitespace ignored.
 
+#### When to use ADDED vs MODIFIED
+- ADDED: Introduces a new capability or sub-capability that can stand alone as a requirement. Prefer ADDED when the change is orthogonal (e.g., adding "Slash Command Configuration") rather than altering the semantics of an existing requirement.
+- MODIFIED: Changes the behavior, scope, or acceptance criteria of an existing requirement. Always paste the full, updated requirement content (header + all scenarios). The archiver will replace the entire requirement with what you provide here; partial deltas will drop previous details.
+- RENAMED: Use when only the name changes. If you also change behavior, use RENAMED (name) plus MODIFIED (content) referencing the new name.
+
+Common pitfall: Using MODIFIED to add a new concern without including the previous text. This causes loss of detail at archive time. If you aren’t explicitly changing the existing requirement, add a new requirement under ADDED instead.
+
+Authoring a MODIFIED requirement correctly:
+1) Locate the existing requirement in \`openspec/specs/<capability>/spec.md\`.
+2) Copy the entire requirement block (from \`### Requirement: ...\` through its scenarios).
+3) Paste it under \`## MODIFIED Requirements\` and edit to reflect the new behavior.
+4) Ensure the header text matches exactly (whitespace-insensitive) and keep at least one \`#### Scenario:\`.
+
 Example for RENAMED:
 \`\`\`markdown
 ## RENAMED Requirements