core-agent

core-agent

A production-grade Go substrate for multi-turn LLM agents, built on the Google Agent Development Kit. Ships the wiring — providers, MCP, skills, permissions, durable sessions, remote attach, an in-process Bubble Tea TUI, and a headless CLI — so downstream projects can focus on their own tools and product logic.

📚 Full documentation: go-steer.github.io/core-agent

Features

Runtime

• Multi-turn conversation via ADK's runner.Runner; parallel tool-call dispatch.
• In-process Bubble Tea TUI as the default TTY surface; --no-tui line REPL fallback; slim build (-tags no_tui) drops the TUI tree entirely.
• agent.RunAutonomous for unattended workers with turn / token / cost / wallclock budgets and model-driven termination; ResumeAutonomous picks up from a durable checkpoint after a crash.
• Long-session survivability: automatic post-turn compaction at ~85% context utilization, subtasks with agentic_* tool wrappers that keep bulk tool output out of the parent's context, and task-boundary checkpoints via mark_task_done. See Context management.

Providers

• Gemini API (GEMINI_API_KEY / GOOGLE_API_KEY) and Vertex AI (ADC + GOOGLE_CLOUD_PROJECT) with server-side GoogleSearch and URLContext wired up.
• Anthropic Claude via api.anthropic.com (ANTHROPIC_API_KEY) and via Vertex AI (ADC + ANTHROPIC_VERTEX_PROJECT_ID) as a native model.LLM adapter.
• Mock providers for credential-free testing: --provider=echo and --provider=scripted --script=path.jsonl; --record-to=path.jsonl captures any real session for later replay.

Instructions, tools, MCP, skills

• AGENTS.md primary + AGENTS.d/*.md overlay directory + @include <path> directive for composable, multi-file system instructions; both user (~/.core-agent/) and project scope, with CLAUDE.md / GEMINI.md fallbacks.
• Built-in tool catalog covering files (read_file, read_many_files, write_file, edit_file, delete_file, stat, list_dir), search (glob, grep), data + network (json_query, fetch_url), shell (bash), planning (todo, opt-in record_plan), and interactive prompting (opt-in ask_user). Disable the whole suite with --no-builtin-tools or specific entries with --disable-tools=bash,write_file.
• MCP servers declared in .agents/mcp.json; stdio and Streamable HTTP transports (including remote MCP with Google OAuth); tools are namespaced (<server>_<tool>) and route through the permission gate.
• Claude-compatible skills auto-discovered from .agents/skills/<name>/SKILL.md (project) and ~/.core-agent/skills/ (user-global).

Permissions

• ask / allow / yolo modes with pattern-based allow/deny lists, path-scope enforcement on file tools, URL-scope allowlist for fetch_url, and a non-overridable bash denylist that catches rm -rf /-class mistakes.
• Plan-first enforcement (permissions.RequirePlanArtifact + record_plan tool + /replan slash): denies mutating tool calls until the model has recorded a plan for the current turn — turns "research → approve → execute" from a prompt convention into a substrate primitive.
• Pluggable Prompter interface so the same gate works in a TTY, headless (--ask=auto), the in-process TUI, or a custom web frontend.

Persistence + observability

• Durable sessions and audit log via eventlog.Open(...) — SQLite (pure-Go, CGO-free), Postgres, or MySQL — with monotonic seq, Since(seq) replay, Watch(seq) live-tail, and a session lock for crash-safe multi-process resume.
• Opt-in OpenTelemetry export (console / OTLP); off by default so a fresh invocation makes zero outbound calls beyond the model.
• Per-model token + cost tracking with layered pricing (daily LiteLLM refresh, per-config overrides, longest-prefix fallback).

Remote attach + operator surface

• Attach API: HTTP + Server-Sent Events live-tail + POST /sessions/<sid>/inject + /wake for headless agents, over mTLS + bearer auth. Read-only GET /sessions/<sid>/{tools,agents,status} and GET /permissions/snapshot endpoints for operator dashboards.
• Remote TUI client (core-agent-tui, separately-versioned binary): thin bubble-tea shell on go-steer/core-tui that attaches to any daemon over the attach API — full slash parity with the in-process TUI (/stats, /context, /compact, /done, /subagent, /btw, /memory, /skills, /mcp, /pricing, /perms, /allow, /deny, /reload), per-turn cost footer, live tool-approval modals over HTTP, mid-turn /inject, session switcher.
• Multi-session daemon: one core-agent daemon serves many concurrent sessions with per-caller identity, ACL (Owner/Viewers/Contributors), permission grants, instruction overlays, and audit attribution. Sessions survive daemon restarts (config change, image upgrade, K8s pod replacement) — a reconnecting TUI resumes transparently. Opt-in via multi_session.enabled: true.
• Attach-config (.agents/config.json attach.* block + ${ENV_VAR} expansion) so a K8s ConfigMap can replace half a dozen CLI flags.
• Peer registration for hub-and-spoke fleet discovery on top of attach.
• Agent-card discovery: opt-in /.well-known/agent-card.json endpoint describing name, description, skills, and required auth in the A2A AgentCard shape so agent registries can index the binary.

Subagents

• In-process: agent.WithSubagents([]*Agent) for synchronous delegation; agent.NewBackgroundAgentManager + spawn_agent / list_agents / check_agent / stop_agent for background subagents the model spawns at runtime.
• Remote: agent.NewSpawnRemoteAgentTool with a consumer-supplied RemoteAgentSpawner for out-of-process spawning (gRPC / K8s Jobs / Cloud Run).
• Subagent events stream into the parent's audit log under a Branch label so the trail stays unified.

Kubernetes triage sidecar (v2.6+)

• cmd/k8s-event-watcher/ — client-go informer that watches Kubernetes Events, filters + dedupes, and injects matched incidents into per-incident sessions on a core-agent daemon. Pairs with the bundled triage skill to drive diagnose → fix → verify loops via the GKE MCP, gated by plan-first. See examples/gke-troubleshoot-agent/.

Optional adapters

• extras/scion-agent/ — runs core-agent inside Scion's container runtime with lifecycle status emission and a sciontool_status tool.
• extras/ax-agent/ (on the axplore branch) — AX gRPC remote-agent packaging.

Install

CLI (Go toolchain, requires Go 1.26+):

go install github.com/go-steer/core-agent/v2/cmd/core-agent@latest

Pre-built binary (Sigstore-signed; linux/darwin × amd64/arm64):

TAG=$(gh release view --repo go-steer/core-agent --json tagName -q .tagName)
OS=$(uname -s | tr A-Z a-z)
ARCH=$(uname -m | sed 's/x86_64/amd64/;s/aarch64/arm64/')
gh release download "$TAG" --repo go-steer/core-agent \
  --pattern "core-agent_${TAG#v}_${OS}_${ARCH}.tar.gz"
tar xzf "core-agent_${TAG#v}_${OS}_${ARCH}.tar.gz"
./core-agent --version

core-agent-tui archives use the same naming pattern. Verification details are in each release's notes footer.

Container images (multi-arch amd64 + arm64; distroless static; Sigstore-signed):

docker pull ghcr.io/go-steer/core-agent:latest        # daemon + in-process TUI
docker pull ghcr.io/go-steer/core-agent-slim:latest   # headless daemon, ~5MB smaller
docker pull ghcr.io/go-steer/core-agent-tui:latest    # remote TUI client only
docker pull ghcr.io/go-steer/k8s-event-watcher:latest # K8s event-triage sidecar

Floating tags: :latest, :X.Y.Z, :X.Y, :X (semver, no v prefix), :main, :main-<sha>.

Library:

go get github.com/go-steer/core-agent/v2

Module path note (post-v2.7): the module path carries the /v2 suffix required by Go's SIVE rule. Consumers upgrading from v2.6 or earlier need to rewrite imports: github.com/go-steer/core-agent/pkg/... → github.com/go-steer/core-agent/v2/pkg/.... Container images and source builds were never affected; only go install ...@v2.X.Y and go get require the migration. Pre-fix tags (v2.0.0 through v2.7.0-dev.4) can't be go installed — use @main, a pinned commit SHA, container images, or a source build for those.

Container variants at a glance

Quick start — CLI

# Gemini API key (either variable works)
GEMINI_API_KEY=... core-agent -p "what's 2+2?"

# Anthropic API key
ANTHROPIC_API_KEY=... core-agent --provider anthropic -p "what's 2+2?"

# Multi-turn TUI (bare invocation; conversation persists across turns)
core-agent

Vertex AI (both Gemini and Claude), scripted providers, .agents/config.json defaults, and the full CLI flag reference live in Getting started.

Quick start — library

package main

import (
    "context"
    "fmt"
    "log"

    "github.com/go-steer/core-agent/v2/pkg/agent"
    "github.com/go-steer/core-agent/v2/pkg/config"
    "github.com/go-steer/core-agent/v2/pkg/models"
    _ "github.com/go-steer/core-agent/v2/pkg/models/gemini"
)

func main() {
    cfg := config.DefaultConfig()
    cfg.Model.Provider = config.ProviderGemini

    provider, err := models.Resolve(cfg)
    if err != nil { log.Fatal(err) }

    ctx := context.Background()
    m, err := provider.Model(ctx, cfg.Model.Name)
    if err != nil { log.Fatal(err) }

    a, err := agent.New(m, agent.WithInstruction("Be concise."))
    if err != nil { log.Fatal(err) }

    for event, err := range a.Run(ctx, "What is the capital of France?") {
        if err != nil { log.Fatal(err) }
        if event.Content == nil { continue }
        for _, p := range event.Content.Parts {
            if p.Text != "" && event.Partial {
                fmt.Print(p.Text)
            }
        }
    }
    fmt.Println()
}

Fuller examples in examples/ — basic, with-tools, streaming, autonomous, autonomous-resume, with-subagent, background-monitor, scheduled-monitor, replay, plan-first, cloud-run-deploy, gke-*.

Documentation

• Site — https://go-steer.github.io/core-agent/
• Design rationale — docs/DESIGN.md
• Release process — docs/release-process.md
• Changelog + stability promise — CHANGELOG.md

The site is built with Astro and Starlight; sources live in docs/site/.

Project layout

core-agent/
├── pkg/                    # public library surface (v1 stability)
│   ├── agent/              # ADK llmagent + runner wrapper; Option pattern
│   ├── attach/             # HTTP + SSE + auth + multi-session daemon
│   ├── config/             # .agents/config.json schema + discovery
│   ├── digest/             # structural digest system for tool responses
│   ├── eventlog/           # durable session.Service + audit/replay stream
│   ├── instruction/        # AGENTS.md / CLAUDE.md / GEMINI.md loader
│   ├── mcp/                # mcp.json schema, stdio/HTTP server lifecycle
│   ├── models/             # provider registry + gemini/ + anthropic/ + mock/
│   ├── permissions/        # ask/allow/yolo gate + denylist + path scope
│   ├── recording/          # LLM-wire recorder for offline replay
│   ├── runner/             # headless (one-shot) + REPL/TUI drivers
│   ├── session/            # JSON transcript persistence
│   ├── skills/             # SKILL.md discovery → ADK skilltoolset
│   ├── telemetry/          # OTEL exporter setup
│   ├── tools/              # built-in tools + GateToolset wrapper
│   └── usage/              # per-turn token + cost tracker
├── cmd/
│   ├── core-agent/         # daemon + CLI + in-process TUI
│   ├── core-agent-tui/     # remote TUI client
│   └── k8s-event-watcher/  # K8s event-triage sidecar
├── extras/scion-agent/     # opt-in Scion runtime adapter
├── examples/               # 15+ worked examples
├── docs/                   # DESIGN.md, release-process.md, Astro site
├── SKILLS/                 # bundled meta-skills (cli-setup, autonomous-setup, library-embedding)
└── dev/                    # build/test/lint/release tooling

The Provider interface is the extension point — register your own model backend with models.Register("name", constructor) and the rest of the stack picks it up.

Project conventions

• .agents/ directory — walked up from the working directory like .git. Holds config.json, mcp.json, skills/<name>/SKILL.md, and per-session JSON transcripts.
• AGENTS.md — project-level system-instruction prefix. CLAUDE.md and GEMINI.md are picked up as fallbacks for repos that already have one.
• ~/.<binary>/sessions.db — durable session storage when --session-db is set. The binary name is derived from os.Executable() so core-agent, adapters, and forks each get their own directory. Override with --session-db-path.

Contributing

• Run dev/tools/ci before opening a PR — same checks GitHub Actions runs (vet, build, lint, mod-tidy, test, vuln scan), in fast-fail order. See dev/README.md.
• Every source file carries the Apache 2.0 header. goheader in dev/tools/lint-go enforces this for .go; run dev/tools/add-license-headers for new shell / YAML / Python files.
• The library is meant to stay narrow. Downstream-specific tools, flags, and slash commands belong in consumer projects.

License

Apache-2.0. See LICENSE.