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+# Contributor Guide
+
+Synapse is a Python application that has Rust modules via pyo3 for performance.
+
+## Dev Environment Tips
+- Source code is primarily in `synapse/`, tests are in `tests/`.
+- Run `poetry install --dev` to install development python dependencies. This will also build and install the Synapse rust code.
+- Use `./scripts-dev/lint.sh` to lint the codebase (this attempts to fix issues as well). This should be run and produce no errors before every commit.
+
+## Testing Instructions
+- Find the CI plan in the .github/workflows folder.
+- Use `poetry run trial tests` to run all unit tests, or `poetry run trial tests.metrics.test_phone_home_stats.PhoneHomeStatsTestCase` (for example) to run a single test case. The commit should pass all tests before you merge.
+- Some typing warnings are expected currently. Fix any test or type *errors* until the whole suite is green.
+- Add or update relevant tests for the code you change, even if nobody asked.