OSS Labs

OSS-backed debugging labs across ecosystems.

Each lab is reverted from a real public bug-fix commit. Filter by language, stack, topic, difficulty, and readiness — drafts stay unplayable until a human review marks them ready.

OSS Labs are training exercises derived from public open-source bug-fix history. Completing a lab is not an upstream contribution or merged PR. Buglyst is not affiliated with these projects.
5Playable nowReviewed & marked ready
5In packagingDrafts under review
4LanguagesJS · Python · Java · C++
28Source reposReal public projects
JavaScript / TypeScript7 labsPython1 labJava1 labC++1 lab
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Showing 10 of 10 OSS labs
JavaScript / TypeScriptnpmEasyPlayable
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Axios keeps a stale content-type for React Native FormData

axios/axios · API & Request Flow

Fix
7b3369a
Parent
b0771a3
Files
463
LOC
67,806
License
MIT
Playable · readyOpen Lab →
JavaScript / TypeScriptnpmMediumPlayable
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Symbol keys dropped when merging axios request config

axios/axios · API & Request Flow

Fix
f70731b
Parent
315ec44
Files
464
LOC
65,972
License
MIT
Playable · readyOpen Lab →
JavaScript / TypeScriptnpmEasyPlayable
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Fastify trusts forwarded host and protocol without a socket guard

fastify/fastify · API & Request Flow

Fix
21b4c3c
Parent
9bbf609
Files
385
LOC
79,438
License
MIT
Playable · readyOpen Lab →
JavaScript / TypeScriptnpmEasyPlayable
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Fastify native server close lifecycle regression

fastify/fastify · API & Request Flow

Fix
c2ba18c
Parent
d33f017
Files
385
LOC
79,226
License
MIT
Playable · readyOpen Lab →
JavaScript / TypeScriptnpmEasyPlayable
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Knex omits RETURNING for an empty-row SQLite insert

knex/knex · Database

Fix
f44f75a
Parent
8198fa6
Files
591
LOC
112,949
License
MIT
Playable · readyOpen Lab →
JavamavenMediumNeeds packaging
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ignoringCollectionOrder false positives with duplicate elements

assertj/assertj · API & Request Flow

Fix
4097e94
Parent
e5e027a
Repo scale
5,242 upstream
Snapshot
1,845 files
License
Apache-2.0

Repo scale: 5,242 upstream files · Packaged snapshot: 1,845 files

Packaging: needs_packaging: java sandbox execution not configured in local pipeline

Needs packagingView details →
JavaScript / TypeScriptnpmMediumNeeds packaging
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validate invalid route logLevel at registration (#6523)

fastify/fastify · Secrets & Auth

Fix
2ae3e1d
Parent
d76dbcd
Files
385
LOC
79,304
License
MIT

Packaging: visible failed after gold

Needs packagingView details →
C++cmakeMediumNeeds packaging
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update() parent pointers not updated after recursive merge with JSON_...

nlohmann/json · Date/Time

Fix
584e6b1
Parent
a69a42a
Repo scale
1,205 upstream
Snapshot
331 files
License
MIT

Repo scale: 1,205 upstream files · Packaged snapshot: 331 files

Packaging: Needs hidden test authoring: upstream commit did not provide a second split test.

Needs packagingView details →
JavaScript / TypeScriptnpmMediumNeeds packaging
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Don't change relative location header on manual redirect (#1105)

node-fetch/node-fetch · API & Request Flow

Fix
5304f3f
Parent
f5d3cf5
Files
53
LOC
7,365
License
MIT

Packaging: visible failed after gold

Needs packagingView details →
PythonpipMediumNeeds packaging
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deprecate Accept-Charset header

pallets/werkzeug · API & Request Flow

Fix
97dec52
Parent
68e1b7b
Files
291
LOC
27,879
License
BSD-3-Clause

Packaging: Secret scan redacted: docs/serving.rst, src/werkzeug/datastructures/auth.py, src/werkzeug/debug/__init__.py, src/werkzeug/urls.py, tests/test_http.py

Needs packagingView details →

infoDraft labs are not playable. Status reflects honest packaging + review state, never a fake availability.

Repos we mine

Source repos in the mining pipeline. Packs open as drafts clear packaging and human review.

28 repos
CLI / Local Mode · Coming soonPlanned

Export OSS Labs to your own machine.

A planned local mode will let advanced users export a lab and run it in their own editor and terminal — keeping the guided browser experience as the default. Not yet available; this is a roadmap teaser, not a shipped feature.

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