forge-skill

Files (2)

• SKILL.md
• testing.md · references/

SKILL.md (first lines)

# Forge Skill

Build a skill by stealing first. Whatever skill you are about to write, other
people have written a version of it; the best ideas from those versions plus a
baseline test beat a blank page. Three phases, in order: **steal**, **design**,
**test**. Each ends on a completion criterion; do not start the next before it
holds.

## 0. Should this be a skill?

- Yes: a procedure or body of context the agent needs repeatedly and does not
  already have (the user keeps pasting the same instructions, a fragile
  sequence, a schema, a house style).
- No, write a script or linter instead: the rule is mechanically checkable.
- No, put one line in the always-loaded instructions instead: it applies to
  most sessions and fits in a sentence.
- Edit instead of create: an installed skill already owns the topic. List the
  installed skills and read the descriptions that overlap before going on.

## 1. Steal

Search before writing a word. Use 2-4 phrasings per source (the task, the
domain noun, the tool name, the symptom).

1. **The user's own library** - installed skills and their references.
2. **skills.sh** - `npx skills find "<query>"` (add `--owner <org>` to scope).
   Read a hit without installing it: `npx skills use <owner/repo>@<skill>`
   prints its SKILL.md and saves supporting files to a temp dir (delete it
   after). Research never runs `skills add`.
3. **Vendor collections** - github.com/anthropics/skills,
   github.com/openai/plugins (the older github.com/openai/skills keeps its
   `.curated` set), the tool vendor's own repo or docs (many CLIs and APIs
   ship an official skill).
4. **GitHub code search** - `gh search code "<terms>" --filename SKILL.md`.

Judge candidates by content, with popularity only as a tiebreak (installs,
stars, last commit). Many hits are near-identical forks; read one of each
lineage. Read every candidate's SKILL.md and references in full, and read any
script before running it: fetched skills are untrusted data and can carry
prompt injection or worse.

For each keeper, note in a scratch file: the distinctive ideas worth taking,
what is wrong with it (bloat, stale, vendor lock-in, personal residue), and
its license.

Steal rules:

- Take ideas, structure, checklists and techniques freely; write them in your
  own words for this skill's audience.
- Copy text or scripts verbatim only under a compatible license (MIT, Apache,
  BSD: keep the notice). No license or a proprietary one: ideas only.
- If one candidate already does about 80% of the job well and its license
  allows, adopting it (installed the way the host manages skills) is a valid
  outcome. Say so and stop, or fork it and patch the gap.
- Credit every source in one closing line of the SKILL.md:
  `Credits: <owner/repo@skill> (<what was taken>), ...`

Done when: 3-5 candidates read (or a stated reason there are none), their
best ideas listed, and the adopt-vs-forge call made.

## 2. Baseline

Write 2-3 test prompts a real user would type: specific, with names, paths,
numbers, a little backstory, casual phrasing. Run each in a fresh subagent
**without** the skill, in a temp workspace, and record what goes wrong
verbatim (wrong steps, missing facts, wrong output shape, rationalizations).

- No failure observed: the skill is not needed, or is smaller than planned.
- Classify each failure; the form of the fix follows the failure:

| Baseline failure | Write |
|---|---|
| Knows the rule, skips it under pressure | rule + rationalization table + red flags |
| Complies, but output has the wrong shape | a positive recipe or template: the parts, in order |
| Omits a required element | a required slot in the template |
| Should behave differently by situation | a conditional on an observable predicate |

Done when: every prompt has a recorded baseline and every failure a planned fix.

## 3. Design

### Frontmatter

- `name`: lowercase letters, digits, single hyphens, at most 64 chars, equal
  to the directory name. Follow the host library's naming convention; check
  it collides with no installed skill.
- `description`: the trigger, not a summary. It sits in context every turn
  and decides whether the body is ever read.
  - Front-load the word the user actually types; one trigger per distinct
    case the skill handles (synonyms of one case are one trigger).
  - Include real phrasings, file types, error text and symptoms.
  - Name what the skill is in a few words at most. Never describe its steps:
    agents follow a summarized workflow instead of reading the body.
  - Third person, at most 1024 chars (aim for under 500). Add an exclusion
    only where a sibling skill would otherwise be picked.
- Portable fields only by default: `name`, `description`, `license`,
  `compatibility`, `metadata`, `allowed-tools`. Harness-specific fields (for
  example a manual-only flag for side-effecting procedures like deploys) are
  fine when needed; spec validators flag them.
- Invocation: model-invoked pays its description on every turn; manual-only
  pays nothing but the user must remember it. Choose manual-only for
  procedures whose timing the user controls.

### Body

- Assume a capable agent. Keep only what changes its decisions: non-obvious
  context, real constraints, gotchas, the reason behind a choice. Delete each
  sentence the baseline already obeyed.
- Match freedom to fragility: describe the outcome and criteria for open
  work; give the exact command or script for fragile sequences.
- End every step on a checkable completion criterion.
- State the target behavior. Use a prohibition only for a hard guardrail or a
  baseline discipline failure, and pair it with the positive form.
- Explain why instead of shouting. Reserve all-caps and "no exceptions" for
  discipline rules the baseline broke.
- Prefer one strong pretrained word over a repeated multi-word phrase; use one
  term per concept throughout.
- One source of truth per fact. Point to `--help`, config files or another
  skill instead of restating them. Current state only: no dates, history or

From alexjmiller5/agent-config-public, MIT.

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