Plugin authoring reference

Plugin authoring reference

This page is a reference, not a how-to — for the step-by-step walkthrough, see Build a Plugin. It documents the constraints of the M365 app-package format itself, and maps each one to where wiqd plugin surfaces it.

Caution

Alpha. The wiqd plugin command tree is enabled by default, but the surface is still alpha and the interface may change without notice.

Package anatomy

The table below lists the files under the project’s appPackage/ directory — the same layout wiqd agent scaffolds. Alongside it, at the project root, sit the wiqd descriptor wiqd.plugin.json, the ATK lifecycle file m365agents.yml, and the per-environment env/.env.<env> files that provision writes.

Path (under appPackage/)	Purpose
manifest.json	The top-level Teams app manifest — declares the app and its components
color.png	Full-color app icon, 192×192
outline.png	Transparent outline icon, 32×32
declarativeAgent.json	The declarative-agent component (if the plugin composes an agent)
instruction.txt	The declarative agent’s instructions, referenced by declarativeAgent.json
skills/<slug>/SKILL.md	A skill component — one folder per skill
ai-plugin.json	An API-plugin manifest, at the package root — present only when a composed agent brings API-plugin actions[]
apiSpecificationFile/	The OpenAPI spec(s) backing those API-plugin actions

A key divergence from hand-authoring: wiqd plugin create pins the manifest to manifestVersion: "1.29" — a numbered, GA Teams schema — rather than hand-editing 1.28 or devPreview. That version choice has a real behavioral consequence for connectors: at 1.29, agentConnectors[] entries are URL-only and mcpToolDescription becomes optional; at 1.28, mcpToolDescription is required, and if its referenced file isn’t included in the upload ZIP the upload fails with an HTTP 400. Authoring against wiqd’s pinned 1.29 schema sidesteps that failure mode entirely — there’s no tool-description file to forget.

SKILL.md frontmatter rules

Every skill’s SKILL.md starts with YAML frontmatter. Two fields are load-bearing:

Field	Constraint
name	1–64 characters, kebab-case, must match its containing folder name exactly
description	1–1024 characters, should contain the trigger phrases that should surface the skill

The single most common authoring mistake is a name that doesn’t match its folder — the two are required to agree, and a mismatch is easy to introduce by renaming one without the other.

Kebab-case, precisely: lowercase alphanumeric characters and hyphens only. No underscores, no uppercase letters, no leading/trailing hyphens, and no consecutive hyphens.

name	Valid?	Why
triage-issues	✅	lowercase, hyphen-separated
triage-issues-v2	✅	digits are fine after a hyphen
Triage_Issues	❌	uppercase letters and an underscore
-triage-issues	❌	leading hyphen
triage--issues	❌	consecutive hyphens
triage-issues-	❌	trailing hyphen

Three-layer context-loading model

A skill’s content loads progressively, not all at once — this keeps a busy plugin’s context footprint small until a specific skill is actually needed:

1. Frontmatter — loaded for every skill at startup, always. This is why description must carry the trigger phrases: it’s the only part of an unused skill an agent has already seen.
2. SKILL.md body — loaded only once a trigger phrase matches and the skill activates.
3. references/ — loaded on demand, only when the active skill’s instructions point at a specific reference file.

A fourth category, scripts/, is never loaded into context at all — scripts are executed, and only their output (not their source) becomes part of the conversation.

Companion-file limits

A skill folder may carry companion files (under references/ and scripts/) subject to:

• At most 20 files per skill.
• At most 5 MB per individual file.
• At most 10 MB total across the skill folder.

Every companion-file path must additionally be:

• Relative — no absolute paths.
• Free of .. path segments, backslashes, and null bytes.
• Not a hidden file — no leading . in the filename.
• Not a Windows reserved name — CON, PRN, AUX, NUL, COM1–COM9, LPT1–LPT9 (with or without an extension) are all rejected.
• Composed of safe filename characters only.

Connector / remote MCP server requirements

An agent connector that fronts a remote MCP server must satisfy:

• HTTPS with TLS 1.2 or later.
• Streamable HTTP transport, speaking JSON-RPC 2.0.
• Support for both the tools/list and tools/call methods.
• Each tool call completing in under 30 seconds.

wiqd’s divergence: wiqd plugin add connector writes a URL-only entry under manifest 1.29 — the server is expected to advertise its own tools at runtime, so wiqd does not scaffold a separate mcpToolDescription file the way a 1.28-schema manifest requires.

add connector also enforces caps before writing, so an out-of-bounds entry never reaches the manifest in the first place:

Field	Cap
Connectors per manifest	≤ 10
id (derived from --name)	≤ 64 characters
displayName (from --name)	≤ 128 characters
description (from --description)	≤ 4000 characters
mcpServerUrl (from --url)	≤ 2048 characters

Auth types

A connector or API plugin can declare one of these authentication types:

• None — no authentication.
• OAuthPluginVault — OAuth, with tokens managed by the plugin vault.
• ApiKeyPluginVault — API-key authentication, with the key managed by the plugin vault. Note that API-key auth is not yet available in Cowork — use OAuth or Dynamic Client Registration (DCR) there instead.

Dynamic Client Registration (DCR) is not itself a manifest auth type — it’s a mechanism where the connector registers its own OAuth client at runtime instead of using a pre-configured client ID. A DCR-backed connector still resolves to the OAuthPluginVault type in the manifest.

wiqd plugin add connector is URL-only today and does not scaffold connector authentication — if your MCP server or API plugin needs auth, configure it directly per the M365 Copilot extensibility documentation; wiqd doesn’t yet automate that step.

Validation codes

Static wiqd plugin validate covers only the declarative-agent (MVL) surface. Everything below surfaces only at wiqd plugin validate --mode deep (package-first AVL) or at upload/submission time — knowing which layer owns which code tells you where in your workflow a given failure will actually appear. The ASKILL-* codes are the Microsoft 365 Copilot platform’s own Agent Skills validation codes (emitted by AVL and at upload), not wiqd-defined — wiqd surfaces them by running deep validation against that platform.

Manifest-level codes

These fire against the manifest’s agentSkills[] array itself, before the package is even inspected — all are severity Error:

Code	Meaning
ASKILL-M001	An agentSkills[] entry is missing its required folder property
ASKILL-M002	The agentSkills array declares more than 20 entries
ASKILL-M003	An agentSkills[] entry’s folder path is longer than 256 characters

Package-level codes

These fire once the referenced skill folders are actually opened inside the ZIP — all are severity Error:

Code	Meaning
ASKILL-P001	The folder an agentSkills[] entry points at doesn’t exist in the package
ASKILL-P002	That folder has no SKILL.md file
ASKILL-P003	SKILL.md’s frontmatter isn’t valid, ----delimited YAML
ASKILL-P004	SKILL.md frontmatter has no name field
ASKILL-P005	SKILL.md frontmatter has no description field
ASKILL-P006	SKILL.md’s name doesn’t match its containing folder’s name
ASKILL-P007	SKILL.md’s name isn’t valid kebab-case
ASKILL-P008	Two or more agentSkills[] entries point at the same folder

Companion-file size and path violations aren’t part of this numbered set — they’re rejected under the rules in Companion-file limits instead.

Connector validation

Connectors are validated as part of the same package-first pass, against a separate set of platform rules rather than numbered ASKILL-* codes:

• Every connector needs both an id and a displayName, and ids must be unique across the manifest’s connector list.
• A connector must pick exactly one tool source — either plugin or remoteMcpServer — never both, never neither.
• mcpServerUrl must be a well-formed HTTPS URL.
• On manifest 1.28, a remoteMcpServer connector must also carry mcpToolDescription, and the file it names must be present in the uploaded ZIP. wiqd’s add connector targets the pinned 1.29 schema and writes URL-only entries, so wiqd-authored connectors never carry this field and never hit this rejection — see Package anatomy for why.
• authorization.referenceId is required whenever the auth type isn’t None, and conversely must be absent when the type is None.

Where each surfaces

Failure class	Surfaces at
Declarative-agent manifest / API-plugin manifest / OpenAPI errors	wiqd plugin validate (static, MVL)
ASKILL-* codes, connector validation rules	wiqd plugin validate --mode deep (package-first, AVL), and at upload/submission
Top-level manifest additionalProperties rejections (a field the Cowork plugin schema doesn’t define, under manifest 1.28)	wiqd plugin validate --mode deep, and at upload/submission — a separate, unnumbered schema rejection, not an ASKILL-* code

Cross-platform SKILL.md portability

SKILL.md follows the open Agent Skills standard, which is not wiqd- or Copilot-specific — the same file format is understood by Claude Code, VS Code / GitHub Copilot, Gemini CLI, Cursor, JetBrains Junie, OpenAI Codex, and other agent hosts. Authoring a skill once and exporting it (see Import / export) is how you carry it to those other tools without hand-translating the format.

Skill-authoring best practices

• Be specific about triggers. Phrase description as “Use when the user asks to…” rather than a generic capability summary — vague descriptions produce skills that either never activate or activate for the wrong requests.
• Write numbered workflow steps that map to concrete, executable actions, not abstract guidance.
• Define an explicit output format so the agent’s response is predictable and testable.
• Reference connector tools by name. If the skill drives an MCP connector, name its tools explicitly rather than describing them vaguely — inspect the server’s advertised tool list before writing the instructions.
• Keep SKILL.md lean. Move detailed or rarely-needed material into references/ — remember the body loads on every trigger, but references load only on demand.
• Never embed secrets in SKILL.md or any companion file. Use connector auth (see Auth types) instead.

Learn-parity table

Every section of the Microsoft Learn “Build plugins for Copilot Cowork” page, mapped to its wiqd equivalent:

Learn section	Status
Package anatomy	Covered here — Package anatomy
Convert a Claude plugin	Covered — wiqd plugin import replaces Convert-ClaudePluginToMOS3.ps1
Create a skill	Covered — Build a Plugin → Path 1 & 2, SKILL.md frontmatter rules
Reference materials	Covered — Three-layer context-loading model
Connector (MCP)	Covered — Connector / remote MCP server requirements
Manifest	Covered — Package anatomy
Icons	Covered — Package anatomy (192×192 / 32×32)
Package (zip with Compress-Archive)	Covered, different mechanism — wiqd plugin package replaces hand-zipping
Test / sideload	Covered, different mechanism — wiqd plugin provision + wiqd plugin share replace raw atk install sideloading
Publish to tenant	Covered — Build a Plugin → Publishing paths
Publish to the public store	Out of scope for wiqd — Partner Center certification/submission is a human/admin step outside wiqd; see Publishing paths
Test connector via dev tunnels	Out of scope for wiqd — wiqd does not manage dev tunnels; expose your MCP server yourself and pass its public https:// URL to wiqd plugin add connector
Packaging patterns	Covered — Package anatomy
Skill best practices	Covered — Skill-authoring best practices
Validation rules	Covered — Validation codes
Cross-platform (Claude, Cursor, etc.)	Covered — Cross-platform SKILL.md portability, wiqd plugin export
MCP annotations	Out of scope for wiqd — wiqd plugin add connector is URL-only and does not scaffold tool-level MCP annotations; the remote server owns them
Common questions	Covered — spread across this page and Build a Plugin; ask the conversational path (see Path 1) for anything not covered

Go deeper

• Build a Plugin — the step-by-step walkthrough (agentic and CLI paths)
• What is a plugin? — the mental model and the three meanings of “skill”
• wiqd plugin — the full command reference
• wiqd plugin validate — static vs. deep validation