{"slug": "theta-a-humble-approach-to-harness-agnostic-configuration", "title": "theta: a humble approach to harness agnostic configuration", "summary": "Tamarillo AI released theta, a Rust command-line tool that functions as a package manager for agent configuration files across multiple AI coding assistants. The tool reads a `theta.toml` manifest and can resolve, lock, and cast configurations to supported harnesses including Claude Code, Codex CLI, GitHub Copilot, and Cursor, enabling developers to manage agent rules, tools, skills, and subagents from a single configuration source.", "body_md": "Rust CLI for managing agent configurations defined by [theta-spec](https://theta-spec.tamarillo.ai/).\n\n```\ncurl -sfL https://raw.githubusercontent.com/tamarillo-ai/theta/main/scripts/install.sh | bash\ntheta init                                     # scaffold theta.toml\ntheta add rule python-types                    # add a rule\ntheta add tool fetch --command \"uvx mcp-server-fetch\"                       # MCP tool (stdio)\ntheta add tool context7 --command \"npx -y @upstash/context7-mcp@latest\"    # another MCP tool\ntheta add skill vercel-labs/agent-skills/skills/web-design-guidelines@main  # skill from GitHub\ntheta check                                    # validate everything\ntheta cast to claude-code                      # --> CLAUDE.md + .mcp.json + .claude/\n```\n\ntheta reads `theta.toml`\n\nand resolves, locks, materializes, and casts agent configurations to any supported harness by solving resources in a common `.theta/`\n\nfolder. Like a package manager but for agent harness resources.\n\nNatively supported harnesses include:\n\n- Claude Code\n- Codex CLI\n- GitHub Copilot\n- Cursor\n\n```\ncd /path/to/your/project\ntheta cast from claude-code\n```\n\n| Group | Commands |\n|---|---|\nLifecycle |\n`init` , `check` , `lock` , `sync` , `cast to` , `cast from` , `tree` |\nDependencies |\n`add rule/system/tool/skill/subagent` , `rm rule/system/tool/skill/subagent` |\nInspection |\n`describe` , `list rules/tools/skills/subagents` |\nSystem store |\n`register skill/rule/agent` , `list store` , `rm store` , `init --from` |\n\nFull docs: [theta](https://theta.tamarillo.ai/), and it is more than recommended to read [theta-spec](https://theta-spec.tamarillo.ai/) first, given that this is the standard that theta implements against.\n\n[Getting started](/tamarillo-ai/theta/blob/main/docs/getting-started.md)[Concepts](/tamarillo-ai/theta/blob/main/docs/concepts/index.md)— manifest, sources, locking, casting, system store[CLI reference](/tamarillo-ai/theta/blob/main/docs/reference/cli.md)— every verb, every flag[Settings](/tamarillo-ai/theta/blob/main/docs/reference/settings.md)— environment variables, directory overrides\n\nOr alternatively build the docs locally:\n\n```\nuv run mkdocs serve --livereload\n```\n\nRegenerate CLI reference from clap definitions:\n\n```\njust gen-cli-docs\n```\n\n[Rust](https://rustup.rs/)stable toolchain (see`rust-version`\n\nin`Cargo.toml`\n\nfor MSRV)[just](https://github.com/casey/just)— task runner (`cargo install just`\n\n)[lefthook](https://github.com/evilmartians/lefthook)— git hooks ([installation guide](https://lefthook.dev/install/))\n\nAll other dev tools (nextest, deny, shear, typos) are installed via `just install-tools`\n\n.\n\n```\ngit clone git@github.com:tamarillo-ai/theta.git\ncd theta\njust setup   # installs dev tools, hooks, fetches deps\njust --list         # see all available recipes\njust test           # local tests (no network)\njust test-online    # tests including live registries\njust check          # run all CI checks locally\njust gen-cli-docs   # regenerate docs/reference/cli.md\njust fmt            # format all code\n```\n\n- See\n[STYLE.md](/tamarillo-ai/theta/blob/main/STYLE.md)for documentation style `clippy::pedantic`\n\nis enabled workspace-wide — check`[workspace.lints.clippy]`\n\nin`Cargo.toml`\n\nfor allowed lints\n\n`theta`\n\nis the canonical implementation of `theta-spec`\n\n. Behavioral changes in `theta`\n\nSHOULD be accompanied by a respective change in `theta-spec`\n\n. Hotfixes, refactors, and non-protocol changes MAY be pushed without a change in `theta-spec`\n\n. Version-modification-triggering changes MUST follow from a TEP.\n\ntheta's architecture is heavily inspired by [uv](https://github.com/astral-sh/uv) by **astral**. Direct signals of devotion, admiration, and almost plagiarism include:\n\n**Settings cascade**— CLI flag > env var > default, inspired by`uv-settings`\n\n(cited in source)**Git fetch and cache**— 3-tier layout (db/checkouts/locks), system git CLI, url digest keying — derived from`uv-git`\n\n**Lock file design**— deterministic manifest hash, content hashing with`sha256:`\n\nprefix, staleness detection, and others— same approach as uv's`toml_edit`\n\nfor formatting preservation`pyproject_mut`\n\n**Materialization lifecycle**—`.theta/`\n\nmirrors uv's`.venv/`\n\n: lock --> materialize --> verify consistency --> cleanup orphans**Output stack**—`owo-colors`\n\n+`anstream`\n\n+`fs-err`\n\n+`indicatif`\n\n[theta-spec](https://theta-spec.tamarillo.ai/)— the standard[Agent Skills spec](https://agentskills.io/specification)— skill packaging format[MCP](https://modelcontextprotocol.io/)— tool protocol[uv](https://github.com/astral-sh/uv)— architectural reference", "url": "https://wpnews.pro/news/theta-a-humble-approach-to-harness-agnostic-configuration", "canonical_source": "https://github.com/tamarillo-ai/theta", "published_at": "2026-05-27 00:29:49+00:00", "updated_at": "2026-05-27 00:39:27.819775+00:00", "lang": "en", "topics": ["ai-agents", "ai-tools", "ai-infrastructure", "ai-products", "ai-startups"], "entities": ["theta", "Claude Code", "Codex CLI", "GitHub Copilot", "Cursor", "tamarillo.ai", "Vercel", "Upstash"], "alternates": {"html": "https://wpnews.pro/news/theta-a-humble-approach-to-harness-agnostic-configuration", "markdown": "https://wpnews.pro/news/theta-a-humble-approach-to-harness-agnostic-configuration.md", "text": "https://wpnews.pro/news/theta-a-humble-approach-to-harness-agnostic-configuration.txt", "jsonld": "https://wpnews.pro/news/theta-a-humble-approach-to-harness-agnostic-configuration.jsonld"}}