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.
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/googlechrome/modern-web-guidance-src/passkeysnpx skills add GoogleChrome/modern-web-guidance-src --skill passkeysgit 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/passkeys)<a href="https://agentmods.dev/skills/googlechrome/modern-web-guidance-src/passkeys"><img src="https://agentmods.dev/badge/skills/googlechrome/modern-web-guidance-src/passkeys.svg" alt="Measured on agentmods" 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 | $0.00053 | $0.00644 |
| Opus 5 | $0.00026 | $0.00322 |
| Sonnet 5 | $0.00011 | $0.00129 |
| Haiku 4.5 | $0.00005 | $0.00064 |
Grade A, and why
passkeys-web 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 5d 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 — 46 lines — stays where its author put it; the contents beside it link to each section on GitHub.
Passkeys Implementation Guide (Web)
This skill provides a modular guide to implementing passkeys
Implementation Phase
- Registration: Allowing users to create new passkeys.
- Authentication: Logging users in with passkeys.
- Management: Listing, renaming, and deleting passkeys.
- Reauthentication: Logging users back in with passkeys.
Evaluation
- Evaluate Passkey Skills: Evaluate passkey skills.
References
You MUST read the following references when implementing their respective features:
- Conditional Create: Read this before implementing automatic passkey creation or conditional create.
- Conditional Mediation: Read this before implementing form autofill based passkey authentication.
- Signal API: Read this before implementing any
PublicKeyCredential.signal*methods. - AAGUID Resolution: Read this before saving a new credential to the database during registration to map the provider name and icon.
Recommended Libraries
For backend, using a library is recommended. Here's a list of recommended open source libraries per language:
- JavaScript/TypeScript: SimpleWebAuthn
- Python: py_webauthn
- Java: Java WebAuthn Server , WebAuthn4J, LINE FIDO2 Server
- .Net: .Net library for FIDO2, WebAuthn.Net
- Go: WebAuthn Go Library, Passkey Server
- Ruby: WebAuthn Ruby
- PHP: WebAuthn PHP Library, WebAuthn Framework
What ships with it
9 files 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.
- 5d ago First seen · 46 lines · 53 tokens per session scan A e230e4792b2a
passkeys-web is a skill published in the GitHub repository GoogleChrome/modern-web-guidance-src (1,014 stars, last pushed today), licensed Apache-2.0. It adds 53 tokens to every session and 644 once invoked, about $0.0003 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.
Other skills, from other repositories
systematic-debugging
Use when encountering any bug, test failure, or unexpected behavior, before proposing fixes.
local-ai-agents
Build local-first AI agents that run entirely on a developer workstation with Microsoft Foundry Local and Qwen function-calling models. Covers Small Language Models (SLMs), the OpenAI-compatible local endpoint, sandboxed local tools, local RAG with Chroma, local MCP servers, hybrid cloud/local routing, and the…
chronicle
Analyze Copilot session history for standup reports, usage tips, session search, and session reindexing. Use when the user asks for a standup, daily summary, usage tips, workflow recommendations, wants to search or find past sessions by keyword/file/PR, wants to reindex their session store, or asks about deleting…
imagegen
Generate or edit raster images when the task benefits from AI-created bitmap visuals such as photos, illustrations, textures, sprites, mockups, or transparent-background cutouts. Use when Codex should create a brand-new image, transform an existing image, or derive visual variants from references, and the output…
chat-pet-sprite-creation
Use when creating or changing VS Code chat pet sprite art, sprite sheets, state animations, eye treatments, Stable/Insiders variants, or pet transitions under src/vs/workbench/contrib/chat/browser/widget/media/chatPet.
cpu-profile-analysis
Analyze V8/Chrome CPU profiles (.cpuprofile) and DevTools trace files (Trace-.json). Use when: profiling performance, investigating slow functions, comparing code paths, finding bottlenecks, analyzing timeToRequest, understanding call trees from sampling profiler data, analyzing layout/paint/rendering, investigating…