Does Skill builder help? Tested on writing skills tasks
Skill builder, from yusufkaraaslan/Skill_Seekers. Its skill authoring tasks were run with the skill loaded and without it. Each time it is the same task, run twice.
What we tested
Whether loading this skill helps a model write a skill document.
What counts as helping
The score with the skill has to beat the score without it by at least 10 percentage points, on the same 10 briefs.
How we scored it
We checked each document against the open Agent Skills specification and counted the rules it passed. The score is the share it passed, from 0 to 1.
Without to with, per model
Via API tested via API
Gemini 3.1 Flash Lite
Holds
GPT-5 mini
Holds
deterministic pass rate, 0 to 1
In Claude Code tested in Claude Code
Claude Fable 5.1 Wider run, three ways
Could not measure
Claude Haiku 4.5 Wider run, three ways
Holds
Claude Opus 5 Wider run, three ways
Could not measure
Claude Sonnet 5 Wider run, three ways
Could not measure
deterministic pass rate, 0 to 1
Show per-task detail
Every item, without and with, per model
Via API tested via API
- GPT-5 mini
- Gemini 3.1 Flash Lite
deterministic pass rate, 0 to 1
Hover or focus an item to read its task and every model’s two values.
Task-paired: these item means are what this cell's interval is built from.
The item means behind this plot
| Item | GPT-5 mini | Gemini 3.1 Flash Lite | ||
|---|---|---|---|---|
| Task | without | with | without | with |
| sa-04 | 0.273 | 1.000 | 0.909 | 1.000 |
| sa-06 | 0.727 | 1.000 | 0.545 | 1.000 |
| sa-08 | 0.909 | 1.000 | 0.364 | 1.000 |
| sa-10 | 0.727 | 1.000 | 0.545 | 1.000 |
| sa-05 | 0.818 | 1.000 | 0.545 | 1.000 |
| sa-07 | 0.545 | 1.000 | 0.909 | 1.000 |
| sa-01 | 0.727 | 1.000 | 0.909 | 1.000 |
| sa-02 | 0.727 | 0.909 | 0.909 | 1.000 |
| sa-09 | 0.727 | 1.000 | 0.909 | 1.000 |
| sa-03 | 0.909 | 0.909 | 0.909 | 1.000 |
Without to with, per model
In Claude Code tested in Claude Code
Claude Haiku 4.5 Expansion cohort (three arms)
Holds
Claude Fable 5.1 Expansion cohort (three arms)
Could not measure
Claude Opus 5 Expansion cohort (three arms)
Could not measure
Claude Sonnet 5 Expansion cohort (three arms)
Could not measure
deterministic pass rate, 0 to 1
The Claude Code runs committed their cells as arm means and intervals rather than as per-item values, so this panel is drawn without to with rather than item by item.
What exactly was tested, and how it was scored
- Repository
- yusufkaraaslan/Skill_Seekers
- Path
- distribution/claude-plugin/skills/skill-builder
- Commit
f3972efa33fa79634b96936acf1fac321cdcf7c1- Content hash
42c7e6285ae80425be3de0f00e0f7caa7dbe93ff043af34595d76be7e3a5da8f- Date tested
- not yet tested
The pin is the whole of this skill's identity here. It resolves at https://github.com/yusufkaraaslan/Skill_Seekers/tree/f3972efa33fa79634b96936acf1fac321cdcf7c1/distribution/claude-plugin/skills/skill-builder, and the content hash is a sha256 over exactly the text the model was given with the skill loaded. Nothing else about the skill appears on this site.
S13-yusufkaraaslan-skill-builder
Loading distribution/claude-plugin/skills/skill-builder from yusufkaraaslan/Skill_Seekers improves outputs on skill authoring tasks.
- Pass criterion
- With-arm mean conformance to the open Agent Skills specification exceeds the without-arm by at least 0.10 on the same 10 briefs at the same model and settings. Key B, the house standard, is reported beside this figure and takes no part in it.
- Scale
- unit. Same scorer, same instrument and same scale as S02-skill-creator. Added 2026-08-31 by the source expansion under R23; adding a row to an instrument does not touch the instrument.
- Task pairs planned per model
- 10
- Notes
- Shares the skill-authoring task set with every other claim in this class, so all of its rows are measured on identical items against one answer key. The slot this claim scores was pinned by the 2026-08-31 source expansion under R23 and NO MODEL HAS BEEN RUN AGAINST IT. The claim exists so the class holds one claim per pinned slot, which is what makes the row comparable the day it is run.
Injected context tokens
| Arm | Context characters | Injected context tokens |
|---|---|---|
| without | 0 | 0 |
| with | 4,428 | 1,039 |
The character count is exact: it is the length of the text the with arm is given, and the content hash above is a sha256 over that same text. The token figure is an estimate at 4.26 characters per token, the ratio the phase 1 run measured over 3,120 calls, and it is labelled an estimate until a run reports its own token counts. The without arm is given the identical prompt and nothing else, so its zero is a measurement rather than a missing value.
Verdict per model
| Model | Reading | Orbit | Without -> with | Effect | 95 percent interval | Task pairs | Model version returned |
|---|---|---|---|---|---|---|---|
| Gemini 3.1 Flash Lite | Deterministic, scored against a committed answer key | Stable | 0.7455 -> 1.0000 | +0.2545 | [0.1196, 0.3895] | 10 pairs, 30 of 30 records | gemini-3.1-flash-lite |
| GPT-5 mini | Deterministic, scored against a committed answer key | Stable (10 of 10 pairs) | 0.7091 -> 0.9818 | +0.2727 | [0.1481, 0.3973] | 10 pairs, 30 of 37 records | gpt-5-mini-2025-08-07 |
- Stable: the treatment arm outscored the control arm by more than the threshold, and the interval excludes zero.
Cost
Defined in the metrics canon. Cost per task divides every dollar spent on an arm by the tasks attempted on it, including tasks whose call returned nothing, because a call that returned nothing was still billed.
Where the with arm did not win
GPT-5 mini, Deterministic, scored against a committed answer key
Drew on 1 of 10 pairs: sa-03.
In Claude Code
These cells are tested in Claude Code, on a subscription path with no API key. They are a second instrument: no figure here is averaged with one tested via API above. How the two were compared.
- Claude Fable 5.1 · could not be measured in the three-arm cohort
- Claude Haiku 4.5 · helped in the three-arm cohort
- Claude Opus 5 · could not be measured in the three-arm cohort
- Claude Sonnet 5 · could not be measured in the three-arm cohort
Expansion cohort (three arms)
one pass over each committed item. Matrix hash 0078cfa8. Pre-registration · Run report.
| Model | No skill | With skill | Delta | Interval | Pairs | Orbit | Injected tokens |
|---|---|---|---|---|---|---|---|
| Claude Fable 5.1 | 1.0000 | 1.0000 | +0.000 | 0.000 to 0.000 | 10 | Unobservable | not measured: this run records the dose per arm, in the doses list |
| Claude Haiku 4.5 | 0.6000 | 1.0000 | +0.400 | 0.293 to 0.507 | 10 | Stable | not measured: this run records the dose per arm, in the doses list |
| Claude Opus 5 | 1.0000 | 1.0000 | +0.000 | 0.000 to 0.000 | 10 | Unobservable | not measured: this run records the dose per arm, in the doses list |
| Claude Sonnet 5 | 1.0000 | 1.0000 | +0.000 | 0.000 to 0.000 | 10 | Unobservable | not measured: this run records the dose per arm, in the doses list |
Key A: the open Agent Skills specification
This class is ranked on conformance to the open specification and on nothing else. The specification is published by neither cohort, it is given to neither arm, and it is pinned like any other artifact: agentskills/agentskills docs at 69ef37e9424c0a7ea9dd2293b559e43ec8176379, content hash b9079c0c10b7930e8c6a20ff2bc10cda2a3343c55185120e3f1116a1a529b220.
| Predicate | What it requires, in our words | Where the specification says it | Scored when |
|---|---|---|---|
frontmatter-present | The document opens with a YAML frontmatter block, and Markdown follows it. | SKILL.md format, opening sentence | always |
frontmatter-name-present | A name field is present. | SKILL.md format, frontmatter table, name row | always |
frontmatter-description-present | A description field is present. | SKILL.md format, frontmatter table, description row | always |
name-within-length-limit | The name is between one and sixty four characters. | name field, first bullet | always |
name-characters-legal | The name uses only lowercase letters, digits and hyphens. | name field, second bullet | always |
name-no-edge-hyphen | The name neither opens nor closes on a hyphen. | name field, third bullet | always |
name-no-consecutive-hyphens | The name carries no run of two hyphens. | name field, fourth bullet | always |
description-within-length-limit | The description is between one and one thousand and twenty four characters. | description field, first bullet | always |
body-present | Instructions follow the frontmatter rather than an empty document. | Body content, opening sentence | always |
within-line-limit | The document stays under the stated line ceiling for a main SKILL.md. | Progressive disclosure, closing line | always |
file-references-one-level-deep | Every relative path the document points at sits at most one directory down. | File references, closing line | always |
compatibility-within-length-limit | If compatibility is given, it stays inside its stated ceiling. | compatibility field, first bullet | the field is offered |
metadata-is-string-map | If metadata is given, it maps string keys to string values. | metadata field, first bullet | the field is offered |
allowed-tools-is-one-string | If allowed-tools is given, it is a single space separated string. | allowed-tools field, first bullet | the field is offered |
A predicate for an optional field a document does not offer is not applicable and leaves the denominator, so a document is never credited for a rule it did not engage.
Key B: the operator's house standard, not ranked
No records exist, so Key B has no figures either. It is described here rather than left out, because a reader deciding what the ranked number means needs to know what the unranked one is.
No interval, no orbit and no verdict appears above, and none can: these are two arm means and the frozen rule is never called on them.
Every figure above is computed at build time from harness/results/runs-skills.jsonl and harness/results/ledger-skills.jsonl, both committed, by the frozen status_v1 rule and the metrics_v1 cost definitions. How a claim gets tested.