Building CLI backend plugins

CLI backend plugins let OpenClaw call a local AI CLI as a text inference backend. The backend appears as a provider prefix in model refs:

acme-cli/acme-large

Use a CLI backend when the upstream integration is already exposed as a local command, when the CLI owns local login state, or as a fallback when API providers are unavailable.

If the upstream service exposes a normal HTTP model API, write a provider plugin instead. If the upstream runtime owns complete agent sessions, tool events, compaction, or background task state, use an agent harness.

What the plugin owns

A CLI backend plugin has three contracts:

Contract	File	Purpose
Package entry	package.json	Points OpenClaw at the plugin runtime module
Manifest ownership	openclaw.plugin.json	Declares the backend id before runtime loads
Runtime registration	index.ts	Calls api.registerCliBackend(...) with command defaults

The manifest is discovery metadata: it does not execute the CLI or register runtime behavior. Runtime behavior starts when the plugin entry calls api.registerCliBackend(...).

Minimal backend plugin

1. Create package metadata

   package.json

   {
     "name": "@acme/openclaw-acme-cli",
     "version": "1.0.0",
     "type": "module",
     "openclaw": {
       "extensions": ["./index.ts"],
       "compat": {
         "pluginApi": ">=2026.3.24-beta.2",
         "minGatewayVersion": "2026.3.24-beta.2"
       },
       "build": {
         "openclawVersion": "2026.3.24-beta.2",
         "pluginSdkVersion": "2026.3.24-beta.2"
       }
     },
     "dependencies": {
       "openclaw": "^2026.3.24"
     },
     "devDependencies": {
       "typescript": "^5.9.0"
     }
   }
   

   Published packages must ship built JavaScript runtime files. If your source entry is ./src/index.ts, add openclaw.runtimeExtensions pointing at the built JavaScript peer. See Entry points.

2. Declare backend ownership

   openclaw.plugin.json

   {
     "id": "acme-cli",
     "name": "Acme CLI",
     "description": "Run Acme's local AI CLI through OpenClaw",
     "cliBackends": ["acme-cli"],
     "setup": {
       "cliBackends": ["acme-cli"],
       "requiresRuntime": false
     },
     "activation": {
       "onStartup": false
     },
     "configSchema": {
       "type": "object",
       "additionalProperties": false
     }
   }
   

   cliBackends is the runtime ownership list; it lets OpenClaw auto-load the plugin when config or model selection mentions acme-cli/....

   setup.cliBackends is the descriptor-first setup surface. Add it when model discovery, onboarding, or status should recognize the backend without loading plugin runtime. Use requiresRuntime: false only when those static descriptors are enough for setup.

3. Register the backend

   index.ts

   import { definePluginEntry } from "openclaw/plugin-sdk/plugin-entry";
   import {
     CLI_FRESH_WATCHDOG_DEFAULTS,
     CLI_RESUME_WATCHDOG_DEFAULTS,
     type CliBackendPlugin,
   } from "openclaw/plugin-sdk/cli-backend";
   
   function buildAcmeCliBackend(): CliBackendPlugin {
     return {
       id: "acme-cli",
       liveTest: {
         defaultModelRef: "acme-cli/acme-large",
         defaultImageProbe: false,
         defaultMcpProbe: false,
         docker: {
           npmPackage: "@acme/acme-cli",
           binaryName: "acme",
         },
       },
       config: {
         command: "acme",
         args: ["chat", "--json"],
         output: "json",
         input: "stdin",
         modelArg: "--model",
         sessionArg: "--session",
         sessionMode: "existing",
         sessionIdFields: ["session_id", "conversation_id"],
         systemPromptFileArg: "--system-file",
         systemPromptWhen: "first",
         imageArg: "--image",
         imageMode: "repeat",
         reliability: {
           watchdog: {
             fresh: { ...CLI_FRESH_WATCHDOG_DEFAULTS },
             resume: { ...CLI_RESUME_WATCHDOG_DEFAULTS },
           },
         },
         serialize: true,
       },
     };
   }
   
   export default definePluginEntry({
     id: "acme-cli",
     name: "Acme CLI",
     description: "Run Acme's local AI CLI through OpenClaw",
     register(api) {
       api.registerCliBackend(buildAcmeCliBackend());
     },
   });
   

   The backend id must match the manifest cliBackends entry. The registered config is only the default; user config under agents.defaults.cliBackends.acme-cli merges over it at runtime.

Config shape

CliBackendConfig describes how OpenClaw should launch and parse the CLI:

Field	Use
command	Binary name or absolute command path
args	Base argv for fresh runs
resumeArgs	Alternate argv for resumed sessions; supports {sessionId}
output / resumeOutput	Parser: json, jsonl, or text
jsonlDialect	JSONL event dialect: claude-stream-json or gemini-stream-json
liveSession	Long-lived CLI process mode (claude-stdio)
input	Prompt transport: arg or stdin
maxPromptArgChars	Max prompt length for arg mode before falling back to stdin
env / clearEnv	Extra env vars to inject, or names to strip before launch
modelArg	Flag used before the model id
modelAliases	Map OpenClaw model ids to CLI-native ids
sessionArg / sessionArgs	How to pass a session id
sessionMode	always, existing, or none
sessionIdFields	JSON fields OpenClaw reads from CLI output
systemPromptArg / systemPromptFileArg	System prompt transport
systemPromptFileConfigArg / systemPromptFileConfigKey	Config-override transport for a system prompt file (for example -c)
systemPromptMode	append or replace
systemPromptWhen	first, always, or never
imageArg / imageMode	Image path flag and how to pass multiple images (repeat or list)
imagePathScope	Where staged image files live before handoff: temp or workspace
serialize	Keep same-backend runs ordered
reseedFromRawTranscriptWhenUncompacted	Opt in to bounded raw-transcript reseed before compaction for safe session resets
reliability.outputLimits	Max raw JSONL chars/lines retained for one live CLI turn (live-session backends)
reliability.watchdog	No-output timeout tuning, separate for fresh vs resumed runs

Prefer the smallest static config that matches the CLI. Add plugin callbacks only for behavior that really belongs to the backend.

Advanced backend hooks

CliBackendPlugin can also define:

Hook	Use
normalizeConfig(config, context)	Rewrite legacy user config after merge
resolveExecutionArgs(ctx)	Add request-scoped flags such as thinking effort or side-question isolation
prepareExecution(ctx)	Create temporary auth, config, or environment bridges before launch
transformSystemPrompt(ctx)	Apply a final CLI-specific system prompt transform
textTransforms	Bidirectional prompt/output replacements
defaultAuthProfileId	Prefer a specific OpenClaw auth profile
authEpochMode	Decide how auth changes invalidate stored CLI sessions
nativeToolMode	Declare whether native tools are absent, always on, or host-selectable
sideQuestionToolMode	Declare disabled native tools for /btw side questions
bundleMcp / bundleMcpMode	Opt into OpenClaw’s loopback MCP tool bridge
ownsNativeCompaction	Backend owns its own compaction - OpenClaw defers
runtimeArtifact	Bound a script launcher to its complete bundled package tree

Keep these hooks provider-owned. Do not add CLI-specific branches to core when a backend hook can express the behavior.

prepareExecution(ctx) receives ctx.contextTokenBudget, the effective token limit selected for the run. Backends that own native compaction can map that budget into their CLI-specific launch contract.

runtimeArtifact is plugin-owned and is not user-overridable. It is consulted only when a live inference turn mints or revalidates verified setup authority; normal CLI runs do not require it. A backend without this declaration cannot mint verified CLI setup authority. A bundled-package-tree declaration names the exact package.json owner and requires the package entrypoint to be the command. OpenClaw hashes the bounded complete installed package tree, including nested dependencies, and fails closed for redirecting symlinks, launchers outside the declared package, required external dependency declarations, oversized trees, and unknown scripts. Declare this only when that tree contains the complete inference implementation; optional tool integrations do not make an external implementation graph safe.

If the same backend also ships a self-contained native executable, list its canonical basenames in nativeExecutableNames. Other native commands remain unverified even when a user overrides the backend command.

ctx.executionMode is "agent" for normal turns and "side-question" for ephemeral /btw calls. Use it when the CLI needs different one-shot flags, such as disabling native tools, session persistence, or resume behavior for BTW. If a backend normally has nativeToolMode: "always-on" but its side-question argv reliably disables those tools, also set sideQuestionToolMode: "disabled"; otherwise OpenClaw fails closed when BTW requires a no-tools CLI run.

Set nativeToolMode: "selectable" only when resolveExecutionArgs can disable every backend-native tool for an individual run. For those restricted runs, ctx.toolAvailability.native is an empty tuple and ctx.toolAvailability.mcp is the exact host-isolated MCP allowlist. The hook must replace conflicting tool flags and return argv that enforces both values; OpenClaw calls it once with the final fresh or resume argv and fails closed when the backend cannot enforce the restriction. MCP names in this context are safe to auto-approve only because the host has already limited the generated MCP configuration to those servers and tools.

ownsNativeCompaction: opting out of OpenClaw compaction

If your backend runs an agent that compacts its own transcript, set ownsNativeCompaction: true so OpenClaw’s safeguard summarizer never runs against its sessions - the CLI compaction lifecycle returns a no-op and the turn proceeds. claude-cli declares it because Claude Code compacts internally with no harness endpoint. Native-harness sessions such as Codex keep routing to their harness compaction endpoint instead.

Only declare it when all of the following hold, or a deferred over-budget session can stay over budget or go stale (OpenClaw no longer rescues it):

• the backend reliably compacts or bounds its own transcript as it nears its window;
• it persists a resumable session so the compacted state survives turns (for example --resume / --session-id);
• it is not a native-harness compaction session - matching agentHarnessId sessions route to the harness endpoint instead.

MCP tool bridge

CLI backends do not receive OpenClaw tools by default. If the CLI can consume an MCP configuration, opt in explicitly:

return {
  id: "acme-cli",
  bundleMcp: true,
  bundleMcpMode: "codex-config-overrides",
  config: {
    command: "acme",
    args: ["chat", "--json"],
    output: "json",
  },
};

Supported bridge modes:

Mode	Use
claude-config-file	CLIs that accept an MCP config file
codex-config-overrides	CLIs that accept config overrides on argv
gemini-system-settings	CLIs that read MCP settings from their system settings directory

Only enable the bridge when the CLI can actually consume it. If the CLI has its own built-in tool layer that cannot be disabled, set nativeToolMode: "always-on" so OpenClaw can fail closed when a caller requires no native tools. If it can disable every native tool per run, use "selectable" with the resolveExecutionArgs contract above.

User configuration

Users can override any backend default:

{
  agents: {
    defaults: {
      cliBackends: {
        "acme-cli": {
          command: "/opt/acme/bin/acme",
          args: ["chat", "--json", "--profile", "work"],
          modelAliases: {
            large: "acme-large-2026",
          },
        },
      },
      model: {
        primary: "openai/gpt-5.6-sol",
        fallbacks: ["acme-cli/large"],
      },
    },
  },
}

Document the minimum override users are likely to need - usually only command when the binary is outside PATH.

Verification

For bundled plugins, add a focused test around the builder and setup registration, then run the plugin’s targeted test lane:

pnpm test extensions/acme-cli

For local or installed plugins, verify discovery and one real model run:

openclaw plugins inspect acme-cli --runtime --json
openclaw agent --message "reply exactly: backend ok" --model acme-cli/acme-large

If the backend supports images or MCP, add a live smoke that proves those paths with the real CLI. Do not rely on static inspection for prompt, image, MCP, or session-resume behavior.

Checklist

package.json has openclaw.extensions and built runtime entries for published packages

openclaw.plugin.json declares cliBackends and intentional activation.onStartup

setup.cliBackends is present when setup/model discovery should see the backend cold

api.registerCliBackend(...) uses the same backend id as the manifest

User overrides under agents.defaults.cliBackends.<id> still win

Session, system prompt, image, and output parser settings match the real CLI contract

Targeted tests and at least one live CLI smoke prove the backend path

Related

• CLI backends - user configuration and runtime behavior
• Building plugins - package and manifest basics
• Plugin SDK overview - registration API reference
• Plugin manifest - cliBackends and setup descriptors
• Agent harness - full external agent runtimes