Astrid

Astrid

A portable, capability-secure operating system for composable software.

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Astrid treats a component the way an operating system treats a process. Every ability is a sealed WebAssembly capsule: it can be composed with other capsules, granted only explicit authority, and replaced without expanding its reach. Astrid is independent of any particular product, model provider, agent loop, user interface, or distribution.

The kernel underneath is small and deliberately dumb. It routes events, enforces capabilities, runs the sandbox, and records the audit trail; it holds no model, tool schema, or business logic. A jailbreak, poisoned tool, or plain bug still cannot read a file, reach a network, or spawn a process outside its grant. Authority is a capability the kernel enforces, not an instruction the model is trusted to follow.

Quick start

brew tap astrid-runtime/tap && brew install astrid
astrid start
astrid status
astrid capsule list

Start with the Book for the architecture or the Contributor Handbook to contribute.

Why Astrid exists

Agent frameworks put trust in the prompt. Astrid puts it in the runtime. An agent is untrusted code executing on your machine with access to your files, your network, and your credentials. Telling it to behave is not a security boundary. An OS-grade boundary is.

• Cryptographic capability model. Every file path, network host, and tool is a signed ed25519

grant scoped to a resource pattern, principal-bound, expiry-checked, and globally revocable. No grant, no access.

• WASM sandbox with no ambient authority. Capsules run in Wasmtime with no syscalls, no file

descriptors, and no host memory. Every external effect is a capability-checked host call over a WIT-typed ABI.

• The kernel is dumb. It instantiates an event bus, loads capsules, and routes IPC bytes under a

capability ACL. It has no LLM handles, no conversation state, and no tool registry. All intelligence lives in capsules, so a capsule bug cannot corrupt shared kernel state.

• Per-principal everything. Each identity gets isolated capsule access, KV data, secrets, home

directory, quotas, and audit chain. One principal can never read another's namespace, and it fails closed if the caller cannot be resolved.

• Signed, hash-linked audit chain. Each entry seals the hash of the one before it and is signed.

Break the chain and the tampering shows.

• Live capsule lifecycle. Install, upgrade, and remove capsules on a running daemon. No restart.

How it works

Frontends (the CLI, the HTTP gateway, Discord, and so on) are uplinks: protocol clients that connect to the daemon over a Unix domain socket and speak in IPC events. There is no Frontend trait. An uplink publishes events and receives responses like any other bus participant.

flowchart TB
    CLI[CLI] -->|IPC events over Unix socket| Kernel
    HTTP[HTTP gateway] -->|IPC events| Kernel
    Discord[Discord] -->|IPC events| Kernel
    Uplinks[Other uplinks] -->|IPC events| Kernel

    subgraph Runtime[Astrid]
        Kernel[Kernel: astrid-daemondumb event routerevent bus - capability ACL - audit chain - Wasmtime sandbox]
        Capsules[WASM Component capsules: wasm32-unknown-unknownproviders - orchestrators - tools - fs - http - sessions - registry - identity]
    end

    Kernel -->|capability-checked host callsastrid:* WIT ABI| Capsules

Capsules communicate exclusively through the bus. Each declares what it needs and what it provides in a Capsule.toml manifest with typed [imports]/[exports] tables; the kernel resolves the dependency graph by topological sort and boots capsules in order. Tools are an IPC convention, not a kernel concept: a tool capsule intercepts tool.v1.execute., and the kernel never sees a tool schema.

The host ABI is the WebAssembly component model with versioned astrid:* WIT packages: fs, io, kv, ipc, net, http, sys, process, approval, identity, elicit, and uplink. Guests import only what their manifest allows, and every call is capability-gated at the boundary.

The security model

Astrid's security is decomposed. There is no single gate every action funnels through. A capsule has no ambient authority, and authorization is enforced by independent, per-area mechanisms, each fail-closed and each enforced where the effect actually happens.

flowchart TB
    Action[A capsule action] --> Sandbox[WASM sandboxno syscalls, file descriptors, or host memoryexternal resources are capability-checked host calls]
    Action --> Manifest[Manifest gatedeclared file, network, and process allow-listempty is deny-all; path traversal and SSRF defenses]
    Action --> IPC[IPC ACLdeclared publish and subscribe topics onlyper-principal routing]
    Action --> Capability[Capability tokened25519, principal-bound, scoped, expiring, revocableper-device tokens can be subset-scoped]
    Action --> Approval[Approval gateonce - session - always - denyallow always mints a token; local egress elicits consent]
    Action --> OS[OS sandboxbwrap on Linux - seatbelt on macOS for native subprocesses]
    Action --> Audit[Audit chainsigned, hash-linked JSONL decisions and callssplit per principal and independently verifiable]

These mechanisms are real and independently tested. There is no unified interceptor orchestrating them. The five-layer gate chapter of The Astrid Book walks each layer against the source.

Install

Homebrew (macOS and Linux):

brew tap astrid-runtime/tap
brew install astrid

From crates.io (requires Rust 1.95+):

cargo install astrid

From source:

git clone https://github.com/astrid-runtime/astrid
cd astrid && cargo build --release   # binary at ./target/release/astrid

Astrid installs four binaries that work together. You only ever invoke astrid; it starts and manages the rest.

| Binary | Role | |---|---| | astrid | CLI uplink. Connects to the daemon over the Unix socket. TUI, headless mode, capsule and agent management. | | astrid-daemon | The kernel process. Loads capsules, routes IPC, enforces capabilities, runs the sandbox. | | astrid-build | Capsule compiler and packager. Builds to wasm32-unknown-unknown. | | astrid-emit | Stdio-to-bus bridge for external hook producers. |

Initial setup

astrid init fetches a distro (a curated capsule bundle), presents a provider multi-select, and prompts for whatever each provider needs, including its API key. Secrets are stored per principal in the secret store, never passed on the command line. init writes a Distro.lock pinning every capsule by BLAKE3 hash, so the same init reproduces the same fleet.

astrid init                              # interactive: pick provider(s), enter keys
astrid init --yes                        # non-interactive, accept defaults
astrid init --offline ./bundle.shuttle   # install a signed bundle, no network
astrid init --distro @yourorg/your-distro

During onboarding the model field discovers the provider's live model list from its /v1/models endpoint. After init, confirm the agent loop is ready, then talk to it:

astrid doctor    # daemon up? capsules ready? an LLM available?
astrid chat      # interactive session; the daemon auto-starts on first use
astrid models    # list the current provider's models (a registry-capsule verb)

Headless and scripting

astrid -p "summarize the git log"                    # single prompt, prints and exits
git diff HEAD~1 | astrid -p "write a commit message" # stdin is appended to the prompt
astrid -p "fix all failing tests" --yes              # auto-approve tool requests
astrid -p "continue" --session "$SID"                # resume by id or name

Daemon lifecycle

astrid start     # persistent daemon (survives terminal close)
astrid status    # PID, uptime, connected clients, loaded capsules
astrid ps        # loaded capsules and their lifecycle state
astrid stop      # graceful shutdown
astrid update    # download, verify, and stage the latest release (self-update alias)

Per-principal isolation

Each principal (agent identity) is a fully isolated tenant: its own capsule access, KV namespace, secrets, home directory, quotas, and audit chain. New principals inherit nothing by default.

astrid agent create ci-bot                     # clean-slate, least-privilege agent
astrid agent create staging --clone production # full profile + state replica
astrid agent modify ci-bot \
  --add-capsule astrid-capsule-fs              # grant access to a capsule's tools
astrid caps show ci-bot                        # inspect capability grants
astrid quota set -a ci-bot --memory 128MB      # per-principal resource limits
astrid pair-device issue --scope use-only      # scope a device token to a subset

Capsule access is enforced kernel-side at dispatch. A principal can only invoke capsules explicitly granted to it, and two principals installing the same capsule bytes share one content-addressed on-disk artifact while getting separate in-memory runtime instances.

Write a capsule

A capsule is a WASM process described by a manifest. The scaffold generates a first-try-compiling project targeting wasm32-unknown-unknown, plus an AUTHORING.md guide.

astrid capsule new my-capsule    # scaffold Capsule.toml, Cargo.toml, src/lib.rs, .cargo/config.toml
cd my-capsule
astrid capsule build             # compile and package
astrid capsule install .         # hot-loaded into the running daemon, no restart

Capsule authors depend on astrid-sdk, which mirrors the std module layout (fs, net, process, env, time, log) and adds Astrid modules (ipc, kv, http, hooks, uplink, identity, approval). The #[capsule] proc macro generates the WASM ABI boilerplate: exports, serialization, and dispatch for tools, commands, hooks, and lifecycle entry points.

use astrid_sdk::prelude::*;

#[derive(Default)]
struct Weather;

#[capsule]
impl Weather {
    #[astrid::tool]
    fn forecast(&self, args: ForecastArgs) -> Result {
        let key = env::var("WEATHER_API_KEY")?;
        let body = http::get(&format!("https://api.example.com/wx?q={}", args.city))?;
        Ok(serde_json::from_slice(&body)?)
    }
}

Building capsules is a first-class workflow in Astrid. The Forge (astrid capsule new plus authoring tools and a scaffolding Skill) is the on-ramp; the direction is an agent that writes, builds, and installs its own capsules within the capability sandbox.

Live capsule lifecycle

astrid capsule install @org/capsule-name   # install and hot-load
astrid capsule update my-capsule           # hot-swap the running instance
astrid capsule remove my-capsule           # live-unload, no restart
astrid capsule list --verbose              # installed capsules with capability metadata
astrid capsule tree                        # imports/exports dependency graph

What's new in 0.9

Five bodies of work plus a security-hardening pass. See [CHANGELOG.md](CHANGELOG.md) for the full list.

• Live capsule lifecycle. Hot-load on install, hot-swap on upgrade, live-unload on remove, all

without a daemon restart.

• Per-principal isolation, hardened end-to-end. Principal-view-aware capsule loading with

content-addressed artifact reuse, kernel-side tool-surface access enforcement, and per-device capability scope threaded through the HTTP gateway.

• LLM provider and model binding. Multi-provider onboarding with live model discovery, plus

gateway routes and astrid models / astrid doctor for per-principal model management and loop-readiness checks.

• Conversation threads over the HTTP gateway. List, fetch, update, delete, and full-text search

threads, plus a per-principal live conversation feed with cross-principal isolation enforced at the bus.

• astrid:http@1.1.0 and operator-configurable limits. Per-request timeouts, redirect policy,

body caps, https-only, and subresource integrity; seven previously-hardcoded ceilings become operator knobs.

• Security. Local-egress consent (transport-origin marker, runtime elicitation, per-capsule and

per-principal grants), an SSRF airlock that closes IP-literal and redirect bypasses, and a hardened supply-chain path (Sigstore attestation, CodeQL, pinned Action SHAs, least-privilege tokens).

Documentation

• The Astrid Book is the canonical reference: the

kernel, the capsule model, the host ABI, the bus, and the security model, grounded in the source with file and line anchors. Start with Getting Started to go from nothing to a working agent in a few minutes.

• Operator guides live in [docs/](docs/): the [unified config schema](docs/config.md),

[LLM model selection](docs/models.md), [distro signing](docs/distro-signing.md), the [gateway deployment runbook](docs/gateway-deployment.md), and [generating a gateway client](docs/gateway-client.md).

Development

cargo build --workspace
cargo test --workspace -- --quiet
cargo clippy --workspace --all-features -- -D warnings
cargo fmt --all -- --check

All crates enforce #![deny(unsafe_code)] except astrid-sys and astrid-sdk, where WASM FFI requires it. Clippy runs at pedantic level and integer-overflow arithmetic is a lint error. Release binaries for macOS and Linux (x86_64 and aarch64) are built on tag push and signed with keyless Sigstore attestations.

Contributing

Contributions are welcome. Astrid uses a tiered contributor system that protects security-critical code while keeping the door open to new contributors. Every pull request must be linked to a GitHub issue. See [CONTRIBUTING.md](CONTRIBUTING.md) for the issue-first workflow and tier descriptions.

Changes to any contract surface (the host ABI, the IPC protocol, the capability model, the manifest schema, or the SDK public API) go through the RFC process in the RFCs repository before implementation.

License

Dual-licensed under [MIT](LICENSE-MIT) and [Apache 2.0](LICENSE-APACHE), at your option.

Copyright (c) 2025-2026 Joshua J. Bouw and Unicity Labs.

Source & license

This open-source MCP server is cataloged on AgentStack and links to its original source — we do not rehost the code.

• Author: astrid-runtime
• Source: astrid-runtime/astrid
• License: Apache-2.0

Install and usage instructions live in the source repository linked above.