126 lines
12 KiB
Markdown
126 lines
12 KiB
Markdown
# Skills, Plugins, and Marketplaces Across Coding Agents (May 2026)
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A practical survey of how coding agents *other than* Claude Code package
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reusable behavior, and how portable those formats actually are.
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> Reference: Claude Code's "Agent Skills" are folders with a `SKILL.md` +
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> YAML frontmatter (`name`, `description`), auto-loaded from
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> `~/.claude/skills/` or `.claude/skills/`. Plugins use
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> `.claude-plugin/plugin.json` and are installed from a marketplace
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> (`.claude-plugin/marketplace.json`) via `/plugin marketplace add` and
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> `/plugin install`. Anthropic published this as an open Agent Skills
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> spec.
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The big picture in 2026: the spec has *largely won*. Most agents now
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either load Anthropic-style `SKILL.md` natively or via a thin shim, and
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**`AGENTS.md` + MCP** are the two cross-agent standards everyone agrees
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on.
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---
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## 1. Gemini CLI (Google)
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- **Equivalent:** "Extensions" (the umbrella) and "Agent Skills" (introduced March 2026).
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- **On-disk format:** Extensions live in `~/.gemini/extensions/<name>/` with a `gemini-extension.json` manifest. They can bundle MCP servers, `GEMINI.md` context, custom slash commands as `.toml`, hooks, sub-agents, themes, and skills. Skills go in `<extension>/skills/<name>/SKILL.md`, or directly in `~/.gemini/skills/` / `.gemini/skills/` for ad-hoc use ([Gemini CLI extensions](https://geminicli.com/docs/extensions/), [reference](https://geminicli.com/docs/extensions/reference/)).
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- **Install / distribution:** `gemini extensions install <github-url-or-path>` clones into the extensions dir; `gemini extensions update` re-pulls. There is an official browseable catalog at [geminicli.com/extensions](https://geminicli.com/extensions/) and a `gemini-cli-extensions` GitHub org ([github.com/gemini-cli-extensions](https://github.com/gemini-cli-extensions)).
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- **Skill-like unit can contain:** prompt + optional supporting files; in extensions, also tools (via MCP), hooks, sub-agents.
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- **Spec compatibility:** The skills format is **deliberately Anthropic-compatible** — same `SKILL.md` + YAML frontmatter ([Google Cloud Community: "Agent Skills"](https://medium.com/google-cloud/your-gemini-cli-extensions-just-got-smarter-introducing-agent-skills-a8fbfa077e7f)). A community shim, [`gemini-cli-skillz`](https://github.com/intellectronica/gemini-cli-skillz), already exposed Anthropic-style skills via MCP before native support landed.
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## 2. OpenCode (sst/opencode)
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- **Equivalent:** "Agent Skills" (native) + "Plugins" (TypeScript hooks).
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- **On-disk format:** `SKILL.md` files with YAML frontmatter (`name`, `description`), under repo `.opencode/skills/` or `~/.config/opencode/skills/` ([Agent Skills | OpenCode](https://opencode.ai/docs/skills/)). Plugins are TS modules registered in config and exposing lifecycle hooks ([Plugins | OpenCode](https://opencode.ai/docs/plugins/)).
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- **Install / distribution:** Mostly **git clone / npm** today. There is no official first-party marketplace UI, but several third-party catalogs exist: [awesome-opencode](https://github.com/awesome-opencode/awesome-opencode), [n-skills](https://github.com/numman-ali/n-skills) (curated, multi-agent), and [BuySkills](https://buyskills.ai/plugins/opencode/) (paid + free).
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- **Skill-like unit:** prompt + supporting files; plugins add tools/hooks. MCP is a first-class tool surface.
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- **Spec compatibility:** **Native Anthropic Agent Skills** — same `SKILL.md` shape, intentionally cross-agent. Drop-in compatible with Claude Code skill folders in practice.
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## 3. Codex CLI (OpenAI)
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- **Equivalent:** **`AGENTS.md`** for always-on instructions, **Agent Skills** for on-demand workflows, and **Plugins** as a packaging layer.
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- **On-disk format:** `AGENTS.md` is plain markdown, layered from repo root downward, concatenated nearest-last so deeper files override ([Codex AGENTS.md guide](https://developers.openai.com/codex/guides/agents-md)). Skills are `SKILL.md` folders, mirroring Anthropic's spec ([Agent Skills – Codex](https://developers.openai.com/codex/skills)). Custom prompts are **deprecated** in favor of skills.
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- **Install / distribution:** Skills can ship inside plugins, which can also bundle "app mappings", MCP server config, and presentation assets in a single package. Distribution is git-based; no centralized marketplace UI as of May 2026.
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- **Skill-like unit:** instructions + optional scripts/resources; plugins add MCP servers and tool config.
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- **Spec compatibility:** **Native Anthropic Agent Skills.** Codex was the first non-Anthropic agent to commit to AGENTS.md, and the second (after Gemini) to ship the skills spec natively.
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## 4. Cursor
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- **Equivalent:** **Rules** (`.cursorrules` legacy, `.cursor/rules/*.mdc` modern), **MCP** for tools, plus **Agent Skills** (added 2026).
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- **On-disk format:** `.cursor/rules/*.mdc` are markdown-with-frontmatter rule files, scoped per-glob and either always-on or auto-attached ([Rules | Cursor Docs](https://cursor.com/docs/rules)). Skills follow `SKILL.md` ([Mastering Cursor 2026](https://rzaeeff.medium.com/mastering-cursor-rules-agent-skills-modes-models-and-best-practices-81908ec4f4a4)).
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- **Install / distribution:** Rules are **manual copy / git**; the community hub is [cursor.directory](https://cursor.directory/) (no in-IDE installer until recently). MCP servers install via Cursor's settings UI.
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- **Skill-like unit:** Rules are prompt-only. Skills can include workflows, hooks, and pull in domain knowledge on demand. Tools come via MCP, not via the rules format.
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- **Spec compatibility:** Cursor reads **AGENTS.md** and now **Anthropic-style `SKILL.md`** folders ([awesome-cursor-skills](https://github.com/spencerpauly/awesome-cursor-skills)). Rules → skills migration is encouraged for richer workflows.
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## 5. Aider
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- **Equivalent:** **Conventions files** (any markdown, loaded with `--read`) and built-in slash commands. No plugin/skill system.
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- **On-disk format:** Plain markdown convention docs (often `CONVENTIONS.md`); `.aider.conf.yml` for config ([Aider docs](https://aider.chat/docs/)).
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- **Install / distribution:** Manual. Aider is intentionally minimal — no marketplace, no plugins.
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- **Skill-like unit:** Effectively a system-prompt fragment. No tool/hook/subagent extensibility beyond what aider builds in.
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- **Spec compatibility:** Reads `AGENTS.md` if you point it at one with `--read AGENTS.md`. Does **not** auto-discover `SKILL.md`. Closest cross-agent surface is "write your conventions in AGENTS.md and `--read` it."
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## 6. Cline / Roo Code
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- **Cline:** Custom instructions file, `.clinerules`, and a first-party **MCP Marketplace** inside the VS Code extension — one-click install of MCP servers ([Roo vs Cline 2026](https://www.morphllm.com/comparisons/roo-code-vs-cline)). No native Anthropic-style skills.
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- **Roo Code:** Forked Cline. Adds **Custom Modes** — named personas (Architect, Debugger, ESP32 Expert, etc.) defined in `.roomodes` JSON, with a **Custom Mode Marketplace / Mode Gallery** for sharing. Supports MCP but no MCP marketplace ([Roo Code docs](https://docs.roocode.com/)).
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- **Note:** Roo Code announced shutdown of all products on **May 15, 2026** ([Morph comparison](https://www.morphllm.com/comparisons/roo-code-vs-cline)); the team is migrating to roomote.dev. Treat Roo formats as legacy.
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- **On-disk format:** `.clinerules` (markdown), `.roomodes` (JSON of mode definitions).
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- **Skill-like unit:** A "mode" is system prompt + tool allowlist + model config — closest non-Anthropic analog to a skill but agent-bound, not a portable folder.
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- **Spec compatibility:** Neither natively loads `SKILL.md`. Both speak MCP.
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## 7. Continue.dev
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- **Equivalent:** `config.yaml` (formerly `config.json`), **custom slash commands**, **rules**, and the **Continue Hub** (rebranded "Mission Control").
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- **On-disk format:** `~/.continue/config.yaml` declares models, context providers, slash commands (named prompt templates), rules, and MCP servers ([Continue config reference](https://docs.continue.dev/reference)).
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- **Install / distribution:** **Hub / Mission Control** is a real web marketplace — browse configs, one-click add, auto-sync across IDEs, share with team ([Hub vs Local](https://docs.continue.dev/guides/understanding-configs)). This is the most polished marketplace UX outside Claude Code.
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- **Skill-like unit:** Slash commands are prompt + optional model routing; rules are always-on context; MCP supplies tools. No equivalent of a self-contained skill folder with hooks + scripts.
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- **Spec compatibility:** Does **not** natively load `SKILL.md`. You'd reimplement a skill as a custom slash command + rule + MCP server.
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---
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## AGENTS.md as the de-facto cross-agent standard
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`AGENTS.md` is the closest thing to a universal coding-agent format today.
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[agents.md](https://agents.md/) reports 60,000+ projects using it, and it's
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read natively by **Codex, Cursor, Copilot, Gemini CLI, OpenCode, and
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Aider** (via `--read`). It's now stewarded by the Agentic AI Foundation
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under the Linux Foundation, alongside MCP and the Goose framework
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([AGNTCon + MCPCon 2026](https://www.aiexpertmagazine.com/agntcon-mcpcon-north-america-2026-everything-you-need-to-know/)).
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Claude Code reads `CLAUDE.md` but most teams symlink or duplicate to
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`AGENTS.md` ([AGENTS.md vs CLAUDE.md](https://hivetrail.com/blog/agents-md-vs-claude-md-cross-tool-standard)).
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It is **prose-only** — no tools, no hooks, no subagents. It's the lowest
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common denominator, and that is its strength.
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## MCP as the cross-agent tool surface
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Every agent in this list speaks MCP: Claude Code, Codex, Gemini CLI,
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OpenCode, Cursor, Cline, Roo, Continue. If you want to ship reusable
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*tools* (not instructions) to N agents with one artifact, MCP is the
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only realistic answer in 2026.
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---
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## What's actually portable today?
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A realistic verdict:
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| Artifact | Portability |
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| **MCP server** | Universal. Works in all 8 agents surveyed. Best surface for tools. |
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| **AGENTS.md** | Near-universal for prose instructions. Codex, Cursor, Gemini, OpenCode, Aider, Copilot. |
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| **Anthropic `SKILL.md` skill** | Native in Claude Code, **Codex, Gemini CLI, OpenCode, Cursor**. Not native in Aider, Cline, Roo, Continue — but most can be shimmed via MCP. This is the new emerging standard for richer-than-prose units. |
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| **Slash commands** | Per-agent. Claude `.md` ≠ Gemini `.toml` ≠ Continue YAML ≠ Cursor. Don't try. |
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| **Hooks** | Per-agent. Claude, OpenCode, Gemini, Codex each have their own hook shapes. |
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| **Subagents / modes / personas** | Per-agent. Claude subagents, Roo modes, Cline modes, Codex subagents — different file shapes, no convergence yet. |
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| **Plugin / marketplace manifest** | Per-agent. Claude `plugin.json`, Gemini `gemini-extension.json`, Codex plugin, OpenCode plugin — not interchangeable. |
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**Practical recipe for a cross-agent capability in 2026:**
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1. Ship tools as an **MCP server** (npm or container).
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2. Ship instructions as **`AGENTS.md`** at repo root, plus a Claude-compatible **`SKILL.md`** folder for richer on-demand workflows (works natively in Claude/Codex/Gemini/OpenCode/Cursor).
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3. Maintain a thin **per-agent plugin manifest** (`.claude-plugin/plugin.json`, `gemini-extension.json`, etc.) that points at the same skills + MCP server. The bodies are reused; only the wrapper differs.
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So: **one artifact for everything is not realistic**, but **two artifacts (MCP + SKILL.md) plus thin per-agent manifests** covers the vast majority of the modern coding-agent landscape.
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> *Caveats: the skill ecosystem moved fast in Q1–Q2 2026 (Codex deprecated custom prompts in April; Roo announced shutdown for May 15; Gemini's skills support is March-2026 new). Verify the latest docs before committing to any format.*
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