Skills

Package instructions and bundled files that the model can auto-invoke or users can trigger with a slash command.

Skills extend what the model can do by packaging reusable instructions as portable units. Each skill is a SKILL.md file plus optional bundled scripts, references, and assets. Hadrian implements the Agent Skills open specification so skills you author for Hadrian also work with other compliant agents and vice versa.

What a skill looks like

Every skill is a directory with at minimum a SKILL.md file containing YAML frontmatter and Markdown instructions:

---
name: pdf-processing
description: Extract PDF text, fill forms, merge files. Use when handling PDFs.
allowed-tools: Bash(python:*) Read
---

# PDF Processing

## When to use this skill

Use this skill when the user needs to work with PDF files.

## How to extract text

1. Run `scripts/extract.py <input.pdf>`
2. Parse the output into a structured summary.

Optional bundled files (kept alongside the SKILL.md) become available to the model on demand:

pdf-processing/
├── SKILL.md            # Required: instructions + metadata
├── scripts/            # Optional: executable code
│   └── extract.py
├── references/         # Optional: docs
│   └── REFERENCE.md
└── assets/             # Optional: templates, data files
    └── template.md

Frontmatter fields

Field	Required	Description
`name`	Yes	Unique per owner. 1–64 lowercase ASCII alphanumerics or hyphens, no leading/trailing/consecutive hyphens.
`description`	Yes	1–1024 chars. Drives model invocation — front-load trigger phrases ("Use when…", "when the user mentions…").
`user_invocable`	No	Default `true`. Set to `false` to hide from the `/` menu; useful for background-knowledge skills the model auto-loads.
`disable_model_invocation`	No	Default `false`. Set to `true` for skills that should only run when the user explicitly picks them.
`allowed_tools`	No	Space-separated list (or YAML array) of tool patterns the skill may use.
`argument_hint`	No	Shown during `/` autocomplete, e.g. `[issue-number]`.
`metadata`	No	Arbitrary key/value pairs preserved verbatim.

Any additional keys are preserved in frontmatter_extra so unknown spec-adjacent fields (for third-party agents) round-trip cleanly.

How the model invokes a skill

Hadrian registers a single Skill function tool with the model whenever one or more skills are enabled for the current session. The tool's description lists each enabled skill by name and description — the model matches user intent against those entries and calls Skill({command: "<name>"}) to load the full instructions.

The executor runs in the browser:

First call — Skill({command: "<name>"}) returns the skill's SKILL.md body plus a manifest of bundled files.
Follow-up calls — Skill({command: "<name>", file: "<path>"}) returns the contents of a specific bundled file referenced in the SKILL.md.

This matches Claude Code's progressive-disclosure model: the main instructions enter context once; reference files load only when needed.

Skills are not injected into the system prompt. The directory lives in the Skill tool's description, so unused skills don't pollute every request.

Like prompt templates, skills belong to one of four owners:

Owner	Visible to
`user`	Only the owning user.
`project`	All members of the project.
`team`	All members of the team.
`organization`	All organization members, subject to RBAC rules on `skill:list/read`.

Chat surfaces all skills the current user can reach. In the admin UI, manage project skills from Project → Skills.

Invoking a skill as a user

Two equivalent ways:

Slash command. Type /<skill-name> in the chat composer. A popover lists matching skills; press Enter or Tab to commit. The composer prefixes your message with a request to use that skill.
Skills button. Click the Skills icon in the chat toolbar to open the popover. Check a skill to enable it for the session — the model may then auto-invoke it when relevant.

Importing skills

Use the Skills button's + menu to import.

From GitHub

Paste a GitHub URL (e.g. https://github.com/anthropics/skills) or owner/repo. Hadrian walks the tree via the public GitHub Contents API, finds every directory containing a SKILL.md, and bundles the adjacent files. Preview the discovered skills and pick which to import.

The unauthenticated GitHub API allows 60 requests/hour. Hadrian caches directory listings in sessionStorage for 10 minutes to soften this, and surfaces the remaining quota in the import modal.

From the filesystem

Choose a folder via the file picker (browsers supporting <input webkitdirectory> — Chromium-based and Safari). Hadrian reads every file under directories containing a SKILL.md.

Binary files are rejected in v1 — skill contents are stored as UTF-8 text.

Configuration

Per-skill size and per-owner limits live under [limits.resource_limits] in hadrian.toml:

[limits.resource_limits]
# Maximum skills per owner (org/team/project/user). Default: 5000.
max_skills_per_owner = 5000

# Maximum total size of a skill's files in bytes (SKILL.md + bundled).
# Default: 512000 (500 KiB). Set to 0 for unlimited.
max_skill_bytes = 512_000

v1 limitations

Text-only files. Binary assets (images, PDFs) are rejected at the API boundary. Future work: base64 encoding or object-storage offload.
Scripts are read-only. The agent can read scripts/ files through the Skill tool but cannot execute them — there is no client-side sandbox in the Hadrian chat UI. Skills that require script execution won't work end-to-end.
Model-invocation is frontend-only. The gateway server does not inspect skills. Custom clients that hit /v1/responses directly must build the Skill tool themselves.

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