Getting it into your agent
One page per mod, every tool's command on it. A separate URL per tool would split the same page into five that compete with each other.
npx agentmods add skills/gridaco/nothing/render-reftestnpx skills add gridaco/nothing --skill render-reftestgit clone --depth 1 https://github.com/gridaco/nothingWhat it costs to keep this loaded
Counted locally with the o200k_base tokenizer, which is exact for GPT models; Claude uses its own tokenizer and its counts differ. Treat this as one consistent yardstick across the catalogue rather than a bill. Prices are per million input tokens.
| Model | Per session | Once invoked |
|---|---|---|
| Fable 5 | $0.00071 | $0.13054 |
| Opus 5 | $0.00036 | $0.06527 |
| Sonnet 5 | $0.00014 | $0.02611 |
| Haiku 4.5 | $0.00007 | $0.01305 |
Grade A, and why
render-reftest scanned grade A with 0 findings against 26 rules in 11 categories — prompt injection, anti-refusal, data exfiltration, privilege escalation, supply chain, agent snooping, system-prompt leakage, SSRF and excessive agency — measured 2d ago.
A static scan of the body, not an audit. Every finding is printed with the line that produced it so you can judge whether it matters here. A mod is markdown that instructs an agent; that is exactly why what it instructs is worth reading.
Nothing flagged
None of the 26 patterns this scan looks for appear in this file: no shell pipes, no recursive deletes, no credential paths, no hidden text, no instruction-override or anti-refusal phrasing, no agent-config snooping. That is not a guarantee, it is the absence of the things that are checkable.
How it starts
The opening of the file, as written. The whole thing — 1,141 lines — stays where its author put it; the contents beside it link to each section on GitHub.
CG Rendering Tests — Reftests & Golden Tests
How to design, name, and review visual rendering tests in this repo.
When to Use This Skill
- Adding a new pixel-comparison test to
crates/grida/ - Reviewing a PR that adds or updates golden images
- Deciding whether a test should be a reftest, golden test, or probe test
- Designing a fixture that can be verified without vision input
- Investigating a flaky or platform-dependent visual test
- Setting up tolerance thresholds for image diff
- Writing honest PR descriptions for rendering changes
Terminology
Use these terms precisely. Misusing them erodes trust in test results.
| Term | Definition |
|---|---|
| Reftest | A test that compares renderer output against an independent reference (oracle) whose correctness is established outside this project — e.g. a W3C-provided PNG for an SVG test case. The oracle is the source of truth; a mismatch means our renderer is wrong. |
| Independent reference / oracle | A rendering produced by a separate, trusted implementation or defined by a specification. We do not control its content. |
| Golden test | A test that compares renderer output against a previously accepted snapshot produced by our own renderer. There is no external truth — the golden file is the expected output because a human reviewed and approved it. Also called a snapshot test. |
| Snapshot test | Synonym for golden test. The snapshot is a frozen output that we assert has not changed. |
| Render regression test | Any test whose purpose is to detect unintended changes in rendering output. Golden tests are regression tests. Reftests are correctness tests. |
| Pixel diff | Byte-level comparison of two raster images. A single differing channel value is a failure (at zero tolerance). |
| Perceptual diff | Comparison in a perceptual color space (e.g. YIQ via the dify crate). Weights differences by human visual sensitivity. More forgiving than raw pixel diff but still quantifiable. |
| rendiff | Rust crate (rendiff v0.2) for histogram-based pixel diffing. Computes a per-channel difference histogram; thresholds are expressed as [(max_diff, max_count), ...] pairs. Used in flatten_rendiff.rs for equivalence tests. Dep in crates/grida/. |
| dify | Rust crate for perceptual image comparison in YIQ color space. Used by grida_dev reftest for SVG reftests. Supports --threshold and --aa (anti-aliasing detection) flags. |
| pixelmatch | Pure-JS perceptual image comparison library. YIQ-based, AA-aware. Used by @grida/reftest. Zero native deps; same conceptual model as dify, slightly different threshold semantics — see parity notes below. |
@grida/reftest |
General-purpose, language-agnostic TS reftest CLI + library at packages/grida-reftest/. Takes two directories of PNGs, diffs, scores, writes the same bucket layout and JSON report as the Rust grida_dev reftest. Does NOT render anything — producers upstream. |
grida_dev reftest |
Rust reftest runner at crates/grida_dev/src/reftest/. SVG-specific: renders SVG via our own grida pipeline, then diffs against a reference PNG. Canonical for SVG. For non-SVG formats, use @grida/reftest with an upstream renderer. |
| refig | Short for "Figma reftest." Fixture suites under fixtures/local/refig/ containing .fig + document.json + images/ + exports/ (oracle PNGs from Figma's Images API). Consumed by a TS render step + @grida/reftest. See fixtures/local/refig/README.md. |
| refbrowser | Short for "headless-browser reftest." HTML/CSS fixtures under fixtures/test-html/L0/ rendered by Playwright Chromium as the oracle vs. our grida htmlcss renderer. Producer script: .agents/skills/render-reftest/scripts/refbrowser_render.ts; diff via @grida/reftest. |
| Tolerance / fuzz | A configured threshold below which pixel differences are ignored. Expressed as a histogram threshold (rendiff) or a YIQ distance (dify / pixelmatch). Required when rasterization is non-deterministic across platforms. |
| Data test | A test that asserts on the scene graph or computed values directly — no rendering needed. E.g. bounding box, resolved transform matrix, computed style. The cheapest possible assertion. |
| Probe test | A test that asserts correctness by reading pixel values at specific coordinates in the rendered output. Requires a purpose-built fixture with a minimal color palette and documented probe points. No full-image comparison needed. |
| Probe-friendly fixture | A fixture explicitly designed for probe testing: minimal colors, no decorative elements, shapes at known coordinates. Often accompanied by a .probe.json file declaring expected pixel values at specific points. |
What ships with it
1 file beside SKILL.md in the same directory: the scripts, references and assets a skill reads on demand. Not counted in the per-session cost; read them before you install if any of them is executable.
What this file has done since we first saw it
Hashed on every crawl. A supply-chain change to an agent config is a question of when, not whether, so the history is kept rather than the latest state alone.
- 2d ago First seen · 1,141 lines · 71 tokens per session scan A c3b489858d4e
render-reftest is a skill published in the GitHub repository gridaco/nothing (43 stars, last pushed 2d ago), licensed Apache-2.0. It adds 71 tokens to every session and 13,054 once invoked, about $0.0004 per session on Opus 5. A static security scan graded it A with 0 findings. No closer match exists in the catalogue, so it is treated as the original; first seen 2026-08-30.
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