S1Code

S1Code

A native Rust coding agent with inspectable decisions and recoverable context.

Plan with a generative model. Choose concrete actions. Review the changes. Resume the work.

[Get started](#get-started) · [How it works](#how-it-works) · [Documentation](#documentation) · [Contributing](CONTRIBUTING.md)

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S1Code brings a coding agent into your terminal: describe a task, inspect its actions and diff, approve changes, and see the actual verification result. Sessions and captured evidence survive restarts.

Its native runtime combines deterministic policy, bounded decisions, and generative reasoning. Claude or OpenAI handles planning and code generation. Optional Jev integration selects among fully specified actions and can help decide which evidence stays in the active context. S1Code owns local tool execution.

> Experimental preview · 0.3.0-rc.8 — macOS and Linux. Source installation > is available; binary distribution details are in the [installation guide](docs/install.md). > See [implementation status](docs/BUILD_STATUS.md) > for verified paths and remaining limits.

What you can do

• Work in a real repository. Search and read source, apply validated patches,

inspect Git changes, and run [supported verification commands](docs/project-checks.md) for Node, Python, Cargo and existing npm scripts.

• Keep the conversation readable. Streaming replies and tool outcomes up front;

candidates, decisions, context and diffs in an optional inspector.

• Control execution. Review exact patches and commands, or preapprove supported

actions for a trusted workspace. Cancel from the keyboard.

• Pick up where you left off. Saved sessions retain requests, artifacts and

activity. Resume without blindly repeating completed tools.

• Recover evicted evidence. Context eviction removes material from the working

set while preserving captured bytes for rehydration without rerunning commands.

• Use the same engine in scripts. Headless mode emits JSONL and persists approval

requests for later review.

Get started

For prebuilt binaries, verification and updates, see [installation](docs/install.md). There is no npm package to install.

Build from source: requires Git and Rust via rustup. The repository pins Rust 1.94.0. Python 3 runs the included parser demo; Windows is currently unsupported.

git clone https://github.com/mertcicekci0/S1Code.git
cd S1Code
cargo install --path . --locked
s1code doctor

Native Claude + Jev

On macOS, save each API key once using a hidden prompt backed by login Keychain:

s1code auth set claude
s1code auth set typesafe

Open S1Code inside the repository you want to work on:

cd /path/to/your/project
s1code

Enter these commands in the S1Code input field, one at a time:

/provider claude
/model opus
/jev typesafe

Then type your task directly:

Find why the parser tests fail, make the smallest correct fix, and run the tests.

Provider and model choices are remembered. Keys are reused from Keychain; never paste them into a task. On Linux, configure ANTHROPIC_API_KEY and TYPESAFE_API_KEY through your environment or secret manager.

Jev is optional. /decision rules uses deterministic selection without a learned decision backend. /eviction jev separately enables Jev-assisted context eviction. Jev credentials and billing are independent of the generation provider.

Managed ChatGPT login

The separate Codex bridge uses the official installed Codex CLI and its managed login:

s1code login codex
s1code run "Investigate and fix the failing parser test" --mode codex

Codex owns execution, internal model turns and context in this mode. This is a delegation to the official runtime, not the native S1Code loop. See [provider setup](docs/providers.md) for CLI compatibility and permissions.

Native OpenAI generation is also available through the Responses API using an OpenAI API key. /claude-code hands the terminal to the installed official Claude Code application; that handoff does not run S1Code's native loop or Jev decisions.

Claude account + optional Jev companion

s1code login claude
s1code account claude
s1code claude-code

Login stays inside the official Claude Code client. To make Jev evidence ranking available there, connect the optional [MCP companion](docs/claude-companion.md). Claude Code retains its tool loop and context; Jev uses a separate TypeSafe key. Native S1Code still uses API-key generation.

In the terminal

| Action | Command or key | | --- | --- | | Inspect activity, decisions, context and diff | Ctrl+O or F2 during a task | | Review the diff from the follow-up field | /diff | | Return from the inspector | Esc | | Cancel a running task | Esc or Ctrl+C | | List saved tasks | /sessions on the home screen | | Resume the latest task in this workspace | /resume on the home screen | | Resume a particular task | /resume ID or a unique ID prefix | | Show setup commands | /help |

Continue a task in its follow-up field to retain the conversation. A new prompt from the home screen starts an independent saved task.

Native patches and processes require approval by default. For a trusted workspace, /permissions full-access preapproves supported actions for the session; /permissions manual restores prompts. Denied actions remain denied. This is not an OS sandbox: approved tests and build scripts execute repository code with your user's filesystem and network access.

How it works

Observe → construct concrete candidates → filter by policy → select
   ↑                                                        ↓
Verify and update ← persist evidence ← execute ← revalidate

The generator supplies plans, complete tool arguments, patches or answers. Forced transitions run directly; ambiguous candidate selection can use Jev. Deterministic policy and workspace checks apply again before execution, regardless of which backend selected the action. Completion requires current verification evidence.

The active context is a working set over durable artifacts. Budget-triggered reversible eviction preserves pinned constraints and dependency groups; evicted content can be retrieved exactly as captured. Historical snapshots stay historical. Rehydration preserves evidence, not a guarantee that a model will ask for it.

Claude prompt-cache usage, provider calls, tool actions and verification outcomes are recorded when exposed. Lower cost, greater speed and better task performance are hypotheses to evaluate, not promises.

Try it without API keys

s1code demo --offline --workspace /tmp/s1code-parser-demo
s1code context-demo --workspace /tmp/s1code-context-demo

Use empty destination directories. The parser demo uses a labeled OFFLINE SIMULATION for generation, with real reads, patch approvals and failing/passing tests. The context demo stores, evicts and rehydrates actual evidence. Neither is a live model demonstration.

For a disposable, budgeted live Claude + Jev task, run this from the source checkout:

python3 scripts/try_live.py task

The launcher shows its request allowance before any API calls and reuses saved macOS keys. See the [demo guide](docs/demo.md) for preparation and interpretation.

Headless use

s1code run "Fix the failing parser test" --provider claude --decision jev --headless
s1code resume  --headless --approve 

Stdout contains machine-readable JSONL; diagnostics go to stderr. Approval is bound to the exact action and its preconditions. A run does not automatically commit or push your changes.

Development

cargo fmt --check
cargo clippy --locked --all-targets -- -D warnings
cargo test --locked
cargo build --locked --release
python3 scripts/release_check.py

Default tests need no credentials or network inference. scripts/check.sh runs the broader local checks; [evaluation](docs/evaluation.md) explains fixture validation, live trials and matched-policy comparisons. Fixture success is not agent success. Provider-restricted results stay private pending clearance.

Documentation

• [Quickstart](docs/quickstart.md) · [Providers and authentication](docs/providers.md)
• [Architecture](docs/architecture.md) · [Implementation status](docs/BUILD_STATUS.md)
• [Demo guide](docs/demo.md) · [Evaluation methodology](docs/evaluation.md)
• [Security](SECURITY.md) · [Privacy](PRIVACY.md) · [Contributing](CONTRIBUTING.md)
• [Changelog](CHANGELOG.md) · [Release process](docs/releasing.md)

License

New project code is [Apache-2.0](LICENSE). Dependencies retain their own licenses; see [third-party notices](THIRDPARTYNOTICES.md). No vendor affiliation or endorsement is claimed. S1Code is a working name; naming availability and trademark clearance have not been established.

Source & license

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

• Author: mertcicekci0
• Source: mertcicekci0/S1Code
• License: Apache-2.0

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