Tarn
API testing that AI agents can write, run, and debug
Tests are .tarn.yaml files — YAML in, structured JSON out. Single binary, zero dependencies. Designed for the AI coding workflow: an LLM writes tests, runs tarn run --format json, parses results, iterates.
name: Health check
steps:
- name: GET /health
request:
method: GET
url: "{{ env.base_url }}/health"
assert:
status: 200
$ tarn run
TARN Running tests/health.tarn.yaml
● Health check
✓ GET /health (4ms)
Results: 1 passed (15ms)
Why Tarn?
- 50% fewer tokens than equivalent TypeScript/Python tests — faster LLM generation, lower cost
- Structured JSON output with request/response on failures — machines parse it, not regex
- Single binary —
curl | sh install, runs in any CI, no runtime needed
- MCP server — direct integration with Claude Code, Cursor, Windsurf
- Everything you need — REST, GraphQL, captures, cookies, multipart, includes, polling, Lua scripting, parallel execution, 7 output formats
Install
# One-liner (macOS / Linux)
curl -fsSL https://raw.githubusercontent.com/NazarKalytiuk/hive/main/install.sh | sh
# Install to a custom directory
TARN_INSTALL_DIR="$HOME/.local/bin" curl -fsSL https://raw.githubusercontent.com/NazarKalytiuk/hive/main/install.sh | sh
# Or build/install from source
cargo install --git https://github.com/NazarKalytiuk/hive.git --bin tarn
Binaries for macOS (Intel & Apple Silicon), Linux (amd64 & arm64), and Windows (amd64 zip) are published on the releases page.
Each release also includes hive-checksums.txt for SHA256 verification and a generated tarn.rb Homebrew formula artifact.
Container path:
ghcr.io/<owner>/tarn:<tag> from the release workflow
Installer notes:
install.sh verifies the downloaded archive against hive-checksums.txtTARN_INSTALL_DIR controls the install destinationHIVE_INSTALL_DIR is still accepted as a backward-compatible alias during the rename transition- Manual verification also works with
shasum -a 256 -c hive-checksums.txt
Quick Start
tarn init # scaffold tests/health + advanced examples/ templates
# Edit tarn.env.yaml to point at your API, or start one on http://localhost:3000
tarn run # run all tests
tarn run tests/health.tarn.yaml # run the scaffolded test directly
tarn fmt --check # verify canonical YAML formatting
tarn run --env staging # use staging environment
tarn run --format json # structured output for LLM/CI
tarn run --watch # re-run on file changes
tarn run --parallel # run files in parallel
tarn list --tag smoke # inspect matching tests without running them
Hello World
Want a fully local demo path from this repo?
PORT=3000 cargo run -p demo-server &
cargo run -p tarn -- run examples/demo-server/hello-world.tarn.yaml
This exercises a local API with no external network dependency.
There are more local scenarios in examples/demo-server/ for redirects, cookies, forms, error responses, and authenticated CRUD flows.
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NazarKalytiuk
NazarKalytiuk