diff --git a/docs/integration/mutation-evidence-accountability-devtools.md b/docs/integration/mutation-evidence-accountability-devtools.md
new file mode 100644
index 0000000..40e699a
--- /dev/null
+++ b/docs/integration/mutation-evidence-accountability-devtools.md
@@ -0,0 +1,83 @@
+# Mutation and Evidence Accountability Devtools Integration
+
+Status: Proposed
+Canonical spec: https://github.com/SourceOS-Linux/sourceos-spec/pull/96
+Tracking issue: https://github.com/SourceOS-Linux/sourceos-devtools/issues/25
+
+## Purpose
+
+This document defines the first `sourceos-devtools` integration slice for SourceOS Mutation and Evidence Accountability.
+
+The canonical schemas, examples, anti-pattern fixtures, and validator live in `SourceOS-Linux/sourceos-spec`. This repository provides the operator/developer CLI wrapper so implementation repos can validate against one shared contract instead of copying schema logic.
+
+## CLI surface
+
+```bash
+python3 bin/sourceosctl mutation-evidence plan
+python3 bin/sourceosctl mutation-evidence inspect --spec-root ../sourceos-spec
+python3 bin/sourceosctl mutation-evidence validate --spec-root ../sourceos-spec
+python3 bin/sourceosctl mutation-evidence fixture-plan
+```
+
+## Commands
+
+### `mutation-evidence plan`
+
+Prints the integration plan, required canonical spec files, downstream implementation repos, and semantic guardrails.
+
+### `mutation-evidence inspect`
+
+Checks whether a local `sourceos-spec` checkout contains the required Mutation and Evidence Accountability files:
+
+- base schema bundle;
+- umbrella primitive schema bundle;
+- valid example fixtures;
+- invalid anti-pattern fixtures;
+- canonical validator.
+
+### `mutation-evidence validate`
+
+Runs the canonical validator from the `sourceos-spec` checkout. The validator checks:
+
+- base examples and anti-patterns;
+- umbrella primitive examples and anti-patterns;
+- no-visible-extension browser attribution guardrails;
+- delegated I/O actor-chain completeness;
+- diagnostic observer-effect clearance blocking;
+- archive extraction path-boundary and cleanup accounting;
+- blind/degraded/missing sensor compromise-clearance blocking.
+
+### `mutation-evidence fixture-plan`
+
+Prints the valid and invalid fixture classes that implementation repos should reproduce or consume.
+
+## Guardrails
+
+The devtools wrapper keeps five guardrails visible to all downstream implementation repos:
+
+1. No clearance when sensors are blind, degraded, or missing.
+2. No extension-primary browser attribution when extension inventory is `none_visible`.
+3. No delegated mutation without a complete actor chain.
+4. No archive extraction without path-boundary and cleanup accounting.
+5. No diagnostic observer-effect clearance with partial or redacted evidence.
+
+## Stack consumers
+
+This integration slice prepares implementation work in:
+
+- `SourceOS-Linux/BearBrowser`
+- `SourceOS-Linux/TurtleTerm`
+- `SourceOS-Linux/sourceos-shell`
+- `SourceOS-Linux/sourceos-syncd`
+- `SourceOS-Linux/sourceos-boot`
+- `SocioProphet/prophet-platform`
+- `SocioProphet/ontogenesis`
+- `SocioProphet/exodus`
+
+## Acceptance criteria
+
+- `sourceosctl mutation-evidence plan` returns 0.
+- `sourceosctl mutation-evidence inspect --spec-root <path>` fails when required spec files are missing.
+- `sourceosctl mutation-evidence inspect --spec-root <path>` passes when required spec files exist.
+- `sourceosctl mutation-evidence validate --spec-root <path>` returns the canonical validator exit code.
+- Tests cover the command surface and validator propagation behavior.
diff --git a/sourceosctl/cli.py b/sourceosctl/cli.py
index 309c38f..81c6c01 100644
--- a/sourceosctl/cli.py
+++ b/sourceosctl/cli.py
@@ -15,6 +15,7 @@
     local_model,
     agent_machine,
     office,
+    mutation_evidence,
 )
 
 
@@ -42,6 +43,46 @@ def build_parser() -> argparse.ArgumentParser:
     profiles_list_p = profiles_sub.add_parser("list", help="List available profiles")
     profiles_list_p.set_defaults(func=profiles.list_profiles)
 
+    # --- mutation-evidence ---
+    mutation_p = sub.add_parser(
+        "mutation-evidence",
+        help="Mutation and Evidence Accountability developer helpers",
+    )
+    mutation_sub = mutation_p.add_subparsers(
+        dest="mutation_evidence_command", metavar="<subcommand>"
+    )
+    mutation_sub.required = True
+
+    def add_spec_root(p):
+        p.add_argument(
+            "--spec-root",
+            default="../sourceos-spec",
+            help="Path to a sourceos-spec checkout containing the canonical schemas and fixtures",
+        )
+
+    mutation_plan_p = mutation_sub.add_parser(
+        "plan", help="Render the mutation/evidence validation integration plan"
+    )
+    add_spec_root(mutation_plan_p)
+    mutation_plan_p.set_defaults(func=mutation_evidence.plan)
+
+    mutation_inspect_p = mutation_sub.add_parser(
+        "inspect", help="Inspect a sourceos-spec checkout for mutation/evidence contract files"
+    )
+    add_spec_root(mutation_inspect_p)
+    mutation_inspect_p.set_defaults(func=mutation_evidence.inspect)
+
+    mutation_validate_p = mutation_sub.add_parser(
+        "validate", help="Run the canonical sourceos-spec mutation/evidence validator"
+    )
+    add_spec_root(mutation_validate_p)
+    mutation_validate_p.set_defaults(func=mutation_evidence.validate)
+
+    mutation_fixture_p = mutation_sub.add_parser(
+        "fixture-plan", help="List required valid and invalid fixture classes"
+    )
+    mutation_fixture_p.set_defaults(func=mutation_evidence.fixture_plan)
+
     # --- nlboot ---
     nlboot_p = sub.add_parser("nlboot", help="NLBoot operator helpers")
     nlboot_sub = nlboot_p.add_subparsers(dest="nlboot_command", metavar="<subcommand>")
diff --git a/sourceosctl/commands/mutation_evidence.py b/sourceosctl/commands/mutation_evidence.py
new file mode 100644
index 0000000..67932bb
--- /dev/null
+++ b/sourceosctl/commands/mutation_evidence.py
@@ -0,0 +1,139 @@
+"""Mutation and Evidence Accountability developer helpers.
+
+This module intentionally treats sourceos-spec as the canonical schema home.
+Devtools provides the operator/developer CLI wrapper and posture checks so every
+implementation repo can validate against the same contract instead of copying
+schema logic.
+"""
+from __future__ import annotations
+
+import json
+import pathlib
+import subprocess
+import sys
+from dataclasses import dataclass
+
+
+REQUIRED_SPEC_PATHS = [
+    "schemas/MutationEvidenceAccountability.schema.json",
+    "schemas/MutationEvidenceUmbrellaPrimitives.schema.json",
+    "examples/mutation-evidence-accountability.examples.json",
+    "examples/mutation-evidence-umbrella.examples.json",
+    "fixtures/anti-patterns/mutation-evidence-accountability.invalid.json",
+    "fixtures/anti-patterns/mutation-evidence-umbrella.invalid.json",
+    "tools/validate_mutation_evidence_accountability.py",
+]
+
+IMPLEMENTATION_REPOS = [
+    "SourceOS-Linux/BearBrowser",
+    "SourceOS-Linux/TurtleTerm",
+    "SourceOS-Linux/sourceos-shell",
+    "SourceOS-Linux/sourceos-syncd",
+    "SourceOS-Linux/sourceos-devtools",
+    "SourceOS-Linux/sourceos-boot",
+    "SocioProphet/prophet-platform",
+    "SocioProphet/ontogenesis",
+    "SocioProphet/exodus",
+]
+
+GUARDRAILS = [
+    "no clearance when sensors are blind, degraded, or missing",
+    "no extension-primary browser attribution when extension inventory is none_visible",
+    "no delegated mutation without a complete actor chain",
+    "no archive extraction without path-boundary and cleanup accounting",
+    "no diagnostic observer-effect clearance with partial or redacted evidence",
+]
+
+
+@dataclass(frozen=True)
+class Check:
+    name: str
+    status: str
+    detail: str
+
+
+def _spec_root(args) -> pathlib.Path:
+    return pathlib.Path(args.spec_root).expanduser().resolve()
+
+
+def _print_checks(checks: list[Check]) -> int:
+    rc = 0
+    for check in checks:
+        marker = {"pass": "ok", "fail": "fail", "warn": "warn"}.get(check.status, check.status)
+        print(f"[{marker}] {check.name}: {check.detail}")
+        if check.status == "fail":
+            rc = 1
+    return rc
+
+
+def _collect_spec_checks(spec_root: pathlib.Path) -> list[Check]:
+    checks = [
+        Check(
+            "spec-root",
+            "pass" if spec_root.exists() and spec_root.is_dir() else "fail",
+            str(spec_root),
+        )
+    ]
+    for rel in REQUIRED_SPEC_PATHS:
+        path = spec_root / rel
+        checks.append(Check(rel, "pass" if path.exists() else "fail", str(path)))
+    return checks
+
+
+def plan(args) -> int:
+    """Render the mutation/evidence devtools integration posture."""
+    spec_root = _spec_root(args)
+    print("SourceOS Mutation and Evidence Accountability devtools plan")
+    print(f"spec_root: {spec_root}")
+    print("canonical_spec_pr: https://github.com/SourceOS-Linux/sourceos-spec/pull/96")
+    print("\nrequired spec files:")
+    for rel in REQUIRED_SPEC_PATHS:
+        print(f"- {rel}")
+    print("\nimplementation repos:")
+    for repo in IMPLEMENTATION_REPOS:
+        print(f"- {repo}")
+    print("\nsemantic guardrails:")
+    for guardrail in GUARDRAILS:
+        print(f"- {guardrail}")
+    return 0
+
+
+def inspect(args) -> int:
+    """Inspect whether a sourceos-spec checkout has the mutation/evidence contract."""
+    return _print_checks(_collect_spec_checks(_spec_root(args)))
+
+
+def validate(args) -> int:
+    """Run the canonical sourceos-spec mutation/evidence validator."""
+    spec_root = _spec_root(args)
+    checks = _collect_spec_checks(spec_root)
+    check_rc = _print_checks(checks)
+    if check_rc != 0:
+        print("mutation/evidence validation skipped: required spec files are missing")
+        return check_rc
+
+    validator = spec_root / "tools" / "validate_mutation_evidence_accountability.py"
+    cmd = [sys.executable, str(validator)]
+    print(f"running: {' '.join(cmd)}")
+    result = subprocess.run(cmd, cwd=str(spec_root), check=False, text=True)
+    return int(result.returncode)
+
+
+def fixture_plan(args) -> int:
+    """Print the fixture classes expected by downstream implementation repos."""
+    fixture_classes = {
+        "valid": [
+            "browser write with no visible extensions",
+            "delegated sync chain with origin/requesting/execution/storage actors",
+            "terminal/archive extraction with path-boundary and cleanup accounting",
+            "diagnostic self-noise with clearance disabled when evidence is partial",
+        ],
+        "invalid": [
+            "extension-primary browser write with extension_inventory_state=none_visible",
+            "delegated mutation without complete actor chain",
+            "diagnostic observer-effect receipt that allows clearance despite redaction",
+            "archive extraction with unknown path class or missing cleanup policy",
+        ],
+    }
+    print(json.dumps(fixture_classes, indent=2, sort_keys=True))
+    return 0
diff --git a/tests/test_mutation_evidence_cli.py b/tests/test_mutation_evidence_cli.py
new file mode 100644
index 0000000..9032bde
--- /dev/null
+++ b/tests/test_mutation_evidence_cli.py
@@ -0,0 +1,74 @@
+"""Tests for SourceOS Mutation and Evidence Accountability devtools CLI."""
+
+from __future__ import annotations
+
+import pathlib
+import stat
+import sys
+import tempfile
+import unittest
+
+_REPO_ROOT = pathlib.Path(__file__).parent.parent
+sys.path.insert(0, str(_REPO_ROOT))
+
+from sourceosctl.cli import main
+from sourceosctl.commands import mutation_evidence
+
+
+REQUIRED_SPEC_PATHS = mutation_evidence.REQUIRED_SPEC_PATHS
+
+
+def _make_spec_root(tmpdir: pathlib.Path, validator_exit: int = 0) -> pathlib.Path:
+    """Create a minimal sourceos-spec-like tree for CLI tests."""
+    spec_root = tmpdir / "sourceos-spec"
+    spec_root.mkdir()
+    for rel in REQUIRED_SPEC_PATHS:
+        path = spec_root / rel
+        path.parent.mkdir(parents=True, exist_ok=True)
+        if rel.endswith("validate_mutation_evidence_accountability.py"):
+            path.write_text(
+                "#!/usr/bin/env python3\n"
+                "import sys\n"
+                f"print('validator fixture exit={validator_exit}')\n"
+                f"raise SystemExit({validator_exit})\n"
+            )
+            path.chmod(path.stat().st_mode | stat.S_IXUSR)
+        else:
+            path.write_text("{}\n")
+    return spec_root
+
+
+class TestMutationEvidenceCli(unittest.TestCase):
+    def test_plan_returns_zero_for_default_spec_root(self):
+        rc = main(["mutation-evidence", "plan"])
+        self.assertEqual(rc, 0)
+
+    def test_fixture_plan_returns_zero(self):
+        rc = main(["mutation-evidence", "fixture-plan"])
+        self.assertEqual(rc, 0)
+
+    def test_inspect_missing_spec_root_fails(self):
+        rc = main(["mutation-evidence", "inspect", "--spec-root", "/nonexistent/sourceos-spec"])
+        self.assertEqual(rc, 1)
+
+    def test_inspect_complete_spec_root_passes(self):
+        with tempfile.TemporaryDirectory() as td:
+            spec_root = _make_spec_root(pathlib.Path(td))
+            rc = main(["mutation-evidence", "inspect", "--spec-root", str(spec_root)])
+            self.assertEqual(rc, 0)
+
+    def test_validate_complete_spec_root_passes_when_validator_passes(self):
+        with tempfile.TemporaryDirectory() as td:
+            spec_root = _make_spec_root(pathlib.Path(td), validator_exit=0)
+            rc = main(["mutation-evidence", "validate", "--spec-root", str(spec_root)])
+            self.assertEqual(rc, 0)
+
+    def test_validate_complete_spec_root_fails_when_validator_fails(self):
+        with tempfile.TemporaryDirectory() as td:
+            spec_root = _make_spec_root(pathlib.Path(td), validator_exit=7)
+            rc = main(["mutation-evidence", "validate", "--spec-root", str(spec_root)])
+            self.assertEqual(rc, 7)
+
+
+if __name__ == "__main__":
+    unittest.main()