Telemetry — MANDATORY. Every api.fabric.microsoft.com call must carry x-ms-fabric-skill: variable-library-cli (az rest: --headers "x-ms-fabric-skill=variable-library-cli"), including every LRO poll, fabric_lro and retry. Snippets omit it — add it anyway.

CRITICAL NOTES

1. To find the workspace details (including its ID) from a workspace name: list all workspaces, then use JMESPath filtering.
2. To find the item details (including its ID) from a workspace ID, item type, and item name: list all items of that type in that workspace, then use JMESPath filtering.
3. Variable Library has two planes: definition files in Git, and active value set item state in the workspace. Do not treat the active value set as a Git edit. The definition plane is authoring; the item-state plane is operations.
4. Variable Library definition requests must omit the format field entirely. Do not send format: null.
5. Skill disambiguation: use variable-library-cli for every Variable Library concern, including the Variable Library side of a consumer reference. Deep authoring of the consumer item itself belongs elsewhere: pipelines to pipeline-migration, notebooks to spark-cli, Dataflow Gen2 to dataflows-cli, Git lifecycle to git-integration-operations-cli, deployment pipeline mechanics to deployment-pipelines-authoring-cli.
6. Clarify before creating on an underspecified request. If a "set up / create a Variable Library" request does not name the variables, their types, defaults, and value sets, ask a clarifying question or present structured options before creating anything. Do not fabricate a configuration and silently create the item without confirming intent. (A concrete, fully specified request needs no confirmation.)
7. When generating consumer code (notebooks, UDFs) that reads a Boolean Variable Library value, coerce it defensively with str(value).lower() == "true". Never use bool(value) on a string: every non-empty string, including "false", is truthy in Python, so bool("false") is always True.
8. Do not write a value set override whose value equals the variable's default. An override pins the value: once written, later edits to the default no longer reach that value set, so a redundant override silently opts the value set out of inheritance. Omit the override and let the value set inherit. Only override where the value genuinely differs.

Fabric Variable Library -- CLI Skill

This one skill owns Fabric Variable Library items: definitions and value sets, the VL side of consumer references, the active value set item state, and Variable Library CI/CD behavior.

It is a mode dispatcher and contains NO procedures. Pick the mode that matches the request from the table below, then read the matching references/<mode>.md file end to end with your file-reading tool BEFORE issuing a single command. That file holds the endpoints, payload shapes, templates and gotchas; acting without it produces wrong payloads and wrong results.

Read it once per session. A file you have already read stays in context, so do not re-read it on a later turn.

Mode selection

Mode	Use when the request ...	Example triggers	Read this first
authoring	creates or changes the library definition: variables, defaults, types, value set override files, settings.json	create variable library, add a variable, valueSets, variableOverrides, valueSetsOrder, updateDefinition	references/authoring.md
consumption	wires a variable into a consumer item, or explains how a consumer resolves it	libraryVariables, notebookutils variableLibrary, pipeline expression, Dataflow Gen2 / copy job / shortcut / UDF / Plan reference	references/consumption.md
operations	reads or switches the active value set, or covers stages, Git serialization and deployment	active value set, activeValueSetName, promote to prod, per-stage values, Git diff, fabric-cicd	references/operations.md

Mode boundary rule

Classify by plane, not by vocabulary. A request that mentions value sets is authoring when it changes the override files and operations when it changes which value set is active in a workspace. Creating valueSets/prod.json is authoring; pointing the prod workspace at it is operations.

consumption covers the Variable Library side of a reference only. Authoring the consumer item's own definition belongs to that item's skill (CRITICAL NOTES 5).

If a request genuinely spans modes, handle them one at a time and read each reference before you start that part. If the mode is ambiguous after reading this table, ask one short clarifying question instead of guessing.

Terminal write -- the step you must not skip

Reading the reference and planning the change is NOT completing the task. Each mutating mode ends with one state-changing call. If you did not issue it, nothing was persisted -- say so explicitly rather than reporting success.

Mode	Terminal write
authoring	POST /v1/workspaces/{ws}/items with type: "VariableLibrary" for a new library, or POST /v1/workspaces/{ws}/items/{id}/updateDefinition to persist an edit. Both send base64 definition parts and must omit format. Building the JSON locally writes nothing.
consumption	the consumer item's own update call, owned by that item's skill. This skill's deliverable is the correct reference contract to place in it.
operations	PATCH /v1/workspaces/{ws}/variableLibraries/{id} with {"properties":{"activeValueSetName":"<name>"}}. This is item state: it does not edit settings.json, variables.json, or valueSets/*.json, and it does not appear in a Git diff.

Before you report the task done, confirm the terminal call returned success and read the artefact back to prove the change landed. For operations, read back with GET /variableLibraries/{id}: the generic /items/{id} omits properties and will not show the active value set.

Shared essentials (all modes)

Resolve the workspace and item first; every mode depends on it.

Task	Reference	Notes
Finding Workspaces and Items in Fabric	COMMON-CLI.md	Mandatory -- read before resolving any workspace or item id
Fabric Topology & Key Concepts	COMMON-CORE.md	Item types, workspaces, capacities
Authentication & Token Acquisition	COMMON-CORE.md	Wrong audience = 401; read before any auth issue
Authentication Recipes	COMMON-CLI.md	az login flows and token acquisition
Fabric REST with az rest	COMMON-CLI.md	Primary access method for this skill
Core Control-Plane REST APIs	COMMON-CORE.md	Pagination, LRO polling, rate limiting
Long-Running Operations (LRO)	COMMON-CLI.md	Create and definition APIs can return 202
VariableLibrary item definition	ITEM-DEFINITIONS-CORE.md	Canonical part paths and field names
Gotchas & Troubleshooting	COMMON-CLI.md	az rest audience, shell escaping, token expiry

Rules

MUST

• Select exactly one mode from the table above before doing anything else.
• Read references/<mode>.md end to end, as your FIRST tool call, before the first command of that mode. Read it ONCE, in a single full read: do not re-open it, do not grep it again, and do not page through it. You already have it.
• Resolve workspace and item ids by listing and filtering, never by guessing a GUID.
• Announce a mode switch explicitly when the request crosses a boundary.
• Treat the reference as instructions, never as the deliverable. After reading it, RUN the documented commands against the live workspace and report the real results.
• Use the canonical part names variables.json, settings.json, and valueSets/<name>.json, with value for defaults and variableOverrides for value set overrides.
• Produce every artefact the user asked for, under the name they used, and keep its heading even when the finding is "none".

PREFER

• The narrowest mode that satisfies the request.
• Reading exactly ONE mode reference. Load a second only when the request genuinely spans modes, and say so before you do.
• Reporting the mode you chose in your first response so the user can correct you.
• Generating JSON bodies with Python or jq so base64 payloads are valid UTF-8 and quoting is stable.
• Recommending fabric-cicd for full deployment automation rather than hand-rolling it here.

AVOID

• Acting from this dispatcher alone -- it intentionally omits the operational detail.
• Stringifying value-set overrides. Each variableOverrides[].value must use the variable's NATIVE JSON type; a stringified boolean or number is rejected with InvalidContent (InvalidValueOrTypeMismatch) despite the REST doc listing the field as String.
• Using defaultValue, values, or format in Variable Library definitions.
• Fabric fab CLI command syntax. It exists, but Variable Library command shapes are not verified here.
• Deep-authoring consumer item definitions (CRITICAL NOTES 5).
• Re-reading or re-grepping a reference you already loaded; it costs turns and tokens.

Examples

User request	Mode	Reference to read
"Create a Variable Library with a dev and prod value set."	authoring	references/authoring.md
"Wire the target_path variable into my ingest pipeline."	consumption	references/consumption.md
"Point the prod workspace at the prod value set after deployment."	operations	references/operations.md
"Why didn't my Git diff show the value set switch?"	operations	references/operations.md
"Add a Boolean flag variable, then read it from a notebook."	authoring, then consumption	both, one at a time