Modern Web Guidance is a source repository for coding-agent skills that provide web-platform guidance, recommended practices, and browser compatibility information. It helps coding agents choose newer web APIs and patterns when generating web applications. The catalogue skills are the guidance produced and maintained by this project.
Borrowing it
Nothing to install: this file belongs to GoogleChrome/modern-web-guidance-src. Take a copy, put it at the same path in your own repository, and replace the rules that are about this project with yours.
curl -O https://raw.githubusercontent.com/GoogleChrome/modern-web-guidance-src/main/.agents/skills/dev-prompt-canary/SKILL.mdgit clone --depth 1 https://github.com/GoogleChrome/modern-web-guidance-srcWrote this? Show the measurements
A badge with what this costs and how it scanned, read live from this page, so it follows the numbers instead of freezing them. Markdown for a README, HTML for a documentation site or a project page.
[](https://agentmods.dev/skills/googlechrome/modern-web-guidance-src/dev-prompt-canary)<a href="https://agentmods.dev/skills/googlechrome/modern-web-guidance-src/dev-prompt-canary"><img src="https://agentmods.dev/badge/skills/googlechrome/modern-web-guidance-src/dev-prompt-canary/github.svg" alt="Measured on agentmods" height="20"></a>Or the 80×15 button, for a site that already has a row of RSS and ATOM ones. Only the verdict fits; the numbers stay here.
<a href="https://agentmods.dev/skills/googlechrome/modern-web-guidance-src/dev-prompt-canary"><img src="https://agentmods.dev/badge/skills/googlechrome/modern-web-guidance-src/dev-prompt-canary.svg" alt="Reviewed on agentmods" width="80" height="20"></a>What 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 5.1 | $0.00106 | $0.01453 |
| Opus 5.5 | $0.00042 | $0.00581 |
| Sonnet 5.5 | $0.00021 | $0.00291 |
| Haiku 4.5 | $0.00011 | $0.00145 |
Grade A, and why
dev-prompt-canary 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 4d 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 — 75 lines — stays where its author put it; the contents beside it link to each section on GitHub.
gd dev Prompt Canary Validation
Unit tests in src/authoring/dev-prompts.test.ts only verify substring presence in prompt templates—they cannot catch behavioral regressions in what the LLM actually generates.
Whenever you modify src/authoring/dev-prompts.ts, src/authoring/dev.ts, src/grading/generate-grader.ts, or src/grading/template.grader.ts, run this fast empirical canary workflow to verify that generated task.md and grader.ts files obey the rules in project-evals.
1. Incremental Regeneration Mechanics (~4 Minutes Total)
Running gd dev <guide> from scratch takes ~25 minutes per guide because it generates 3 golden solution patches, a zero-passrate.patch, task.md, grader.ts, and runs full evaluations.
Instead, use dev.ts's incremental file-existence checks inside a throwaway worktree:
task.mdOnly (~45s for 8 targets): Keep existing patches and graders untouched. CallextractGuideDescription+buildTargetTaskPrompt+runAgentin a small runner script (or delete onlytargets/<app>/task.mdand rundevGuide(dir, { test: false, targets: [app] })).grader.tsOnly (~2–3 mins per target): Keeptargets/<app>/patches/*-solution.patch,zero-passrate.patch, andtask.mduntouched. Delete onlytargets/<app>/grader.ts, then rundevGuide(dir, { test: false, targets: [app] })to regenerate and calibrategrader.ts.
2. Execution Workflow
Step 1: Create an Isolated Scratch Worktree
Never mutate guides/ inside your active feature worktree. Branch a temporary worktree off your candidate commit:
git worktree add -B exp/canary-eval .worktrees/canary-eval HEAD
ln -s ../../node_modules .worktrees/canary-eval/node_modules
ln -s ../../.env .worktrees/canary-eval/.env
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.
- 4d ago First seen · 75 lines · 106 tokens per session scan A cd2f2991b17c
dev-prompt-canary is a skill published in the GitHub repository GoogleChrome/modern-web-guidance-src (1,202 stars, last pushed today), licensed Apache-2.0. It adds 106 tokens to every session and 1,453 once invoked, about $0.0004 per session on Opus 5.5. 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 2026-10-23.
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