# Aback Skills

> A free, verified marketplace for agent skills. Authors publish a `SKILL.md`
> for free. An admin reviews it. Once approved it is publicly available and
> any agent that speaks the Model Context Protocol can install it into a
> project with a single tool call.

Publishing is free on every plan, with no listing fee, no upload limit and
no revenue share. The paid plans pay for MCP access at scale, and nothing
else.

## What a skill is

A skill is a markdown file, `SKILL.md`, that teaches an agent how to do one
specific thing well. It has sections for Instructions, Rules and Examples.
It is a prompt, a procedure and a set of examples, in a format an agent can
read at the point of use.

## How to use the catalogue

The delivery channel is an MCP server at:

    POST https://abackskills.com/mcp

It speaks the Model Context Protocol over Streamable HTTP and is stateless.
Authenticate with an API key:

    Authorization: Bearer abk_live_<key>

Create a key at https://abackskills.com/dashboard/mcp. The secret is shown
exactly once and is never stored. Clients that cannot set headers may pass
the key as an `api_key` query parameter instead.

## Tools

| Tool | Purpose |
| --- | --- |
| `search_skills` | Search the approved catalogue by text, category or tag |
| `get_skill` | Read one approved skill, with its risk signals and full content |
| `install_skill` | Install a skill into a project and return the files to write |
| `list_installed_skills` | List what is installed in a project |
| `remove_skill` | Remove an installation from a project |
| `list_projects` | List the install targets on the account |
| `check_updates` | Compare installed versions against the latest approved version |
| `get_usage` | Report the current allowance and how much of it is used |

## Installing a skill

`install_skill` returns the exact file path and the exact file content. The
server cannot write to your machine, so the client writes the file. The
default target directory is `.agents/skills`, which is the cross-agent
convention. Pass `target_dir` to use a different layout.

    {
      "jsonrpc": "2.0",
      "id": 1,
      "method": "tools/call",
      "params": {
        "name": "install_skill",
        "arguments": { "slug": "code-review", "project": "my-app" }
      }
    }

The result carries a `contentHash`. Verify the write against it.

## Reading a skill without installing it

The content of an approved skill is also available as an MCP resource:

    aback://skills/{slug}
    aback://skills/{slug}/{version}

And through the public REST API, which needs no key and has no quota:

    GET https://abackskills.com/api/skills?query=code
    GET https://abackskills.com/api/skills/{slug}

## Before you act on a skill

Every approved skill carries risk signals: a score, and whether it contains
external links, scripts or commands. Read them before you act on the skill.
A high score is not a defect, it is information: the skill probably needs a
command to do its job, and you should know what that command is.

## The free tier is real

Every account gets an API key and a monthly allowance. A resolution is one
call that returns skill content. A search costs a tenth of a resolution.
Publishing is never metered, on any plan.

## Links

- Catalogue: https://abackskills.com/skills
- MCP guide: https://abackskills.com/docs/mcp
- Pricing: https://abackskills.com/pricing
- Full documentation for agents: https://abackskills.com/llms-full.txt