derivation-join-collections SKILL.md skillA
derivation-join-collections from estuary/agent-skills is an agent skill: a SKILL.md folder an AI agent loads when a task calls for it.
mdr add estuary/agent-skills/derivation-join-collections@git:20260924.c6e4810Pins git:20260924.c6e4810 in mdr.lock. Pin the fingerprint instead.
- Audit grade
- A, 17 of 17 checks passed
- Kind
- SKILL.md skill
- Repository
- estuary/agent-skills
- Path
skills/derivation-join-collections/SKILL.md- Versions recorded
- 2
- Latest version
- git:20260924.c6e4810, committed Sep 24, 2026
- First version recorded
- Jul 7, 2026
- Size
- 14,717 bytes
- Repository stars
- 7
- License
- Apache-2.0
Create an Estuary derivation that joins two or more collections on a shared key, merging their fields into a single enriched collection. Use for data enrichment, denormalisation, building wide tables for BI, and real-time CDC joins. Derivations add complexity and cost — confirm the user wants a derivation before reaching for this (a destination-side SQL join or BI tool view is often simpler). Use when user says "join-collections derivation", "derivation to join two collections…
Collected from public GitHub. Every version is saved exactly as it was and never changes. Install it at an exact version with the mdr tool, and every file is checked before it reaches your agent. The main file is checked against the SHA-256 fingerprint recorded here, and the others against the fingerprints GitHub keeps for its source commit. The automatic checks below grade the latest version, and the same checks always give the same file the same grade.
What the file says
# derivation-join-collections Estuary derivation that merges documents from multiple source collections into a single collection, keyed on a shared join field. Fields from each source contribute, and Estuary's reduction engine merges them. **Prereq:** read `derivation-basics` first for concepts, the stateless-vs-stateful distinction, and reduction-annotation mechanics. **Docs:** - https://docs.estuary.dev/guides/howto_join_two_collections_typescript/ — official TypeScript walkthrough - https://docs.estuary.dev/reference/reduction-strategies/ — reduction strategy reference (critical for joins) **Canonical examples in the Flow repo** (cover the three join shapes — see "Join types" below): - [join-outer.flow.yaml](https://github.com/estuary/flow/blob/master/examples/derive-patterns/join-outer.flow.yaml) — full outer (reduction-based, no state) - [join-inner.flow.yaml](https://github.com/estuary/flow/blob/master/examples/derive-patterns/join-inner.flow.yaml) — inner (SQLite state, both sides must match) - [join-one-sided.flow.yaml](https://github.com/estuary/flow/blob/master/examples/derive-patterns/join-one-sided.flow.yaml) — left / right (SQLite state, one side drives emission) …
Read the whole file at its exact version.
How to install
mdr add estuary/agent-skills/derivation-join-collections@sha256:9b9faa5660e8b9e9The line at the top of this page pins the label git:20260924.c6e4810, which is what most people want. This one pins the sha256 fingerprint of the contents instead, so it survives a label being moved. Either way the exact version is written to mdr.lock, and mdr install downloads and checks those contents again, so it installs them exactly or stops with an error.
[](https://markdownregistry.com/a/art_l43gzrhiqm74pmxd)
2 badge image fetches in 30 days. What the badge shows.
Versions
The registry has recorded 2 versions of this file, between Jul 7, 2026 and Sep 24, 2026, about one every 79 days.
| version | committed | commit | size | audit | |
|---|---|---|---|---|---|
| git:20260924.c6e4810 latest | 2026-09-24 | c6e4810 | 14,717 B | A | view · diff |
| git:20260707.6b608bf | 2026-07-07 | 6b608bf | 14,680 B | A | view |
Audit of the latest version
- pass: Frontmatter block present
- pass: Frontmatter declares a name
- pass: Frontmatter declares a description
- pass: Size between 200 bytes and 200 KB (14717 bytes)
- pass: No zero-width or bidi control characters
- pass: No instruction hidden inside an HTML comment
- pass: No link to an exfiltration or paste host
- pass: No credential-shaped string
- pass: No instruction to send local credentials anywhere
- pass: No text hidden with inline styles
- pass: No prompt-injection phrasing
- pass: No curl or wget piped into a shell
- pass: No recursive delete of root, home or parent
- pass: No instruction to read or print local credentials
- pass: No base64 blob over 200 characters
- pass: No link to a raw IP address
- pass: No script tag
Source
estuary/agent-skills · 7 stars · license Apache-2.0 · pushed 2026-11-04 · branch main
API
GET https://markdownregistry.com/api/v1/artifacts/art_l43gzrhiqm74pmxd GET https://markdownregistry.com/api/v1/resolve?ref=estuary/agent-skills/derivation-join-collections GET https://markdownregistry.com/api/v1/blob/9b9faa5660e8b9e929dead1dee2d01b5cc32895131bfdde46b3660126b02f8aa
Your AI assistant does the legwork. You hear about the deals worth your word. Hand yours the standing instructions at modelranch.com and it joins the network that reads files like this one.
Guides: the SKILL.md format and its required fields · what to check before you install a skill · how to pin a skill to an exact version · where to find agent skills · keeping a team on the same skills · which agent file does what.