Grim authoring

Grim Artifact Authoring

Grim publishes five artifact kinds to OCI registries. Each has its own source shape, frontmatter schema, and validation gates. This root file holds the invariants that apply to every kind; per-kind depth lives in references/, loaded via the routing table below.

The Five Kinds

grim build and grim release infer the kind from the path — except agents (always --kind agent, or they silently pack as rules) and MCP servers (always --kind mcp, or the .toml is treated as a bundle).

Kind	Source shape	Inference	Installs as
Skill	Directory with a SKILL.md index	directory → skill	Directory tree under the client's skills/ dir
Rule	Single .md file	.md → rule	rules/<name>.md, per-client transform
Rule + support dir	<name>.md + sibling <name>/ dir	sibling dir auto-discovered	Index file + rules/<name>/… side by side
Agent	Single .md, frontmatter required	never — --kind agent mandatory	One agent file per client, per-client render
MCP server	.toml descriptor with a [server] table	never — --kind mcp mandatory	Entry in each client's MCP config file, per-client render
Bundle	.toml member list	.toml → bundle	Never materializes — expands to its members

Which Clients Host Which Kind

Grim installs into ten clients, and not every client can host every kind — decide this before you author, because it changes what you write:

• Skills install everywhere. The universal kind.
• Rules are native for Claude Code, Copilot, Cursor, and Kiro; degraded for OpenCode (the file installs, its path scoping does not); and declined by Codex, Junie, Gemini, Zed, and Amp — grim warns, skips, and writes no file. Half the fleet cannot scope instructions: when the audience is broad, a skill reaches clients a rule never will.
• Agents install for Claude Code, OpenCode, Copilot, Codex, Cursor, and Gemini. Kiro, Junie, Zed, and Amp decline them.
• MCP servers register for all ten, but only Claude accepts the ws transport and the [server.oauth] block; every other client skips such a descriptor with a warning.

A declined kind is an honest refusal, not a silent failure — but it is still zero files. The enforced matrix and the upstream reason behind every degrade and decline: Client Compatibility. A compatibility: frontmatter field is a human-facing hint only and never overrides it.

Universal Invariants

• Names are [a-z0-9] runs joined by single hyphens or periods ([a-z0-9]+([.-][a-z0-9]+)*) — non-empty, ≤ 64 chars, no leading or trailing separator, no adjacent separators (a--b and a..b are invalid). Periods are a grim superset of the Agent Skills standard ([a-z0-9-]) — prefer hyphens when portability to strict-standard tooling matters.
• A skill's name must equal its directory name; an agent's name must equal its file stem. Rule names come from the file stem and obey the same character rules. Bundle and MCP names also come from the file stem but are not charset-validated at build; bundle member names are validated against the same rules at resolve time.
• Any violation of the validated names fails grim build/grim release with exit code 65.
• Unknown top-level frontmatter keys are preserved round-trip (forward compatibility) — never rejected, so a typo'd optional key is silent.

The Metadata-Location Asymmetry

Where catalog metadata (summary, keywords, repository, deprecated, replaced-by) is authored differs by kind. This is the #1 authoring confusion — misplaced keys are not errors, they just silently never reach the catalog:

Kind	summary / keywords / repository / deprecated / replaced-by live…
Skill	inside the metadata: map of SKILL.md frontmatter
Agent	inside the metadata: map of the agent frontmatter
Rule	at the top level of the rule frontmatter (not in metadata)
MCP server	as top-level TOML keys, above the [server] table (replaced-by not read for MCP)
Bundle	as top-level TOML keys, above the member tables

In every kind, keywords is one comma-separated string and repository must be an https:// URL (anything else fails the release with 65). The deprecated notice obeys the same per-kind location; an empty or whitespace-only value means not deprecated and emits no annotation. replaced-by names the successor artifact, authored independently of deprecated; its value must parse as a reference or the release fails with 65 — detail in Publishing.

Companion: Content Craft

This skill covers grim packaging and validation only — including opt-in git provenance at build/release time (--git); confirm flags with grim release --help. For the craft of the content itself — progressive disclosure, context budgets, description triggering, choosing skill vs rule vs agent — read the companion skill ai-config-authoring at ../ai-config-authoring/SKILL.md; both ship together in the grim-essentials bundle. When creating a new artifact from scratch, read it FIRST — write good content, then package it here. If that file is missing, install it by identifier:

grim add ghcr.io/grimoire-rs/skills/ai-config-authoring:0   # installs by default
# fresh project (no grimoire.toml yet): run `grim init` first

The Local Dev Loop

Iterate on an artifact before its first release with local path sources — no registry round-trip:

• grim install <path> — dev-install: renders the working tree into the clients without declaring anything (grimoire.toml and grimoire.lock stay untouched). The record is marked dev in grim status, refreshed by grim update, removed by grim uninstall.
• grim add <path> — declares the local path in the config and pins it by content hash, like any other source. Re-adding over an output you hand-edited in a client is refused as modified; grim add <path> --force is the sanctioned overwrite.

A path is anything starting ./ or ../, or absolute. Both commands cover skills, rules, and agents only; kind is inferred from the path's shape exactly as grim build infers it (directory → skill, bare .md → rule, --kind agent for agents). A local bundle is declared directly in the config's [bundles] table instead (grim add --kind bundle <path> refuses with a hint); its members must be registry references — a local bundle has no registry identity to resolve a relative member against. Typical loop: edit → grim build <path> (validation) → grim install <path> (see it in a real client) → repeat → release. Confirm flags with grim install --help.

Routing Table

Read…	…when
references/skill-spec.md	Authoring a skill directory or its SKILL.md frontmatter
references/rule-spec.md	Authoring a rule file, its globs, or a support directory
references/agent-spec.md	Authoring an agent definition or its vendor overrides
references/mcp-spec.md	Authoring an MCP server descriptor or its env references
references/bundle-spec.md	Authoring a bundle TOML or choosing pinning strategy
references/vendor-metadata.md	Adding a key in any of the ten reserved <vendor>.* namespaces (claude.*, opencode.*, copilot.*, codex.*, cursor.*, kiro.*, junie.*, gemini.*, zed.*, amp.*)
references/release-checklist.md	Before grim release/grim publish, batch manifests, description companions, or triaging an exit-65 failure
references/bootstrap-existing-repo.md	Turning an existing skill repo (agentskills.io skills/<name>/SKILL.md or .claude/skills/) into a grim publisher — inventorying artifacts, fixing names, backfilling catalog metadata, wiring publish CI
references/updating.md	Maintaining this skill package itself

Schema Authority

This skill teaches the craft and the pitfalls; the authoritative schema reference is the Grimoire docs site. When a field table here feels incomplete, the docs page is the source of truth: Artifact Reference · Vendor-Specific Metadata · Publishing · Agent Artifacts · Client Compatibility. For the TOML surfaces, grim schema --kind <config|publish|lock|mcp> prints the JSON Schema generated from grim's own parsers — bind it in your editor to catch manifest typos before any command runs.

Verify Before Acting

grim build <path> validates without pushing — run it after every edit; its output is ground truth for the grim version actually installed. On any conflict between this skill and grim build output or grim --help, trust the tool. Treat this skill as the map, not the territory.

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Verified against the grim release this package ships beside.