bandw

A self-hosted, W&B-compatible experiment tracking backend. The official wandb Python SDK points at it instead of api.wandb.ai.

Quick Start

# Build and run the server (SQLite, no Docker needed)
just build
./bin/server

# Or with MySQL
docker compose up -d
just run

Then point the SDK at it:

import wandb

wandb.login(key="1dbac5a5d91172ad159b7978bec36bb8c3b0a5f5", host="http://localhost:8080")
run = wandb.init(project="my-project", config={"lr": 0.001})
wandb.log({"loss": 0.5, "accuracy": 0.9})
run.finish()

SDK Conformance Report Card

We run the upstream W&B SDK system tests directly against our backend to validate protocol compatibility. The wandb-sdk repo is vendored as a Git submodule and tests are executed via a spy proxy that intercepts SDK-to-backend traffic.

# Run the full conformance suite
./tests/wandb-conformance/run.sh

# Quick smoke test (~8 tests, ~10 seconds)
./tests/wandb-conformance/run.sh --quick

Current Results (Phase 1 -- Init/Log/Finish)

Category	Passing	Source File
Metrics	37 / 37	test_metric_full.py
Run Logging	17 / 41	test_wandb_run.py
Labels	16 / 16	test_label_full.py
Settings	10 / 10	test_wandb_settings.py
Disabled Mode	9 / 9	test_mode_disabled_full.py
File Stream	9 / 10	test_file_stream.py
Init (UpsertBucket)	7 / 12	test_wandb_init.py
Init Reinit	6 / 6	test_wandb_init_reinit.py
Setup	5 / 5	test_wandb_setup.py
Resume (auto)	5 / 5	test_resume_auto.py
Telemetry	4 / 4	test_telemetry_full.py
Login	1 / 5	test_wandb_login.py
Time Resolution	1 / 1	test_time_resolution.py
Total	129 / 161	~20 seconds with -n auto

Merge gate: Do not merge code that causes regressions in this suite. Run ./tests/wandb-conformance/run.sh before merging.

Testing

# Go unit/integration tests (in-memory SQLite, no external deps)
just test

# SDK conformance tests -- full suite (requires uv + Go)
./tests/wandb-conformance/run.sh

# SDK conformance tests -- quick smoke test
./tests/wandb-conformance/run.sh --quick

Project Structure

cmd/server/        Go server entrypoint
internal/          Go backend packages
  authctx/         Auth context helpers
  config/          Environment + CLI flag config
  filestream/      REST file_stream handler
  graphql/         GraphQL resolvers
  server/          HTTP router + middleware
  store/           GORM models + DB operations
  testutil/        In-process test harness
tests/
  wandb-conformance/  SDK conformance test runner + config
docs/              Specs, plans, GraphQL schema
wandb-sdk/         W&B SDK submodule (test suite source)

Docs

• Execution Plan -- 31 slices across 7 phases
• Architecture -- directory layout and design
• GraphQL Schema -- full SDL from the SDK
• System Spec -- backend service specification