agentmods.dev

update-v8-version

A guide for updating the pinned V8 JavaScript engine version used by Codex and its Rust bindings. It covers repository files, checksums, build artifacts, and release-candidate validation.

In plain words
What is it for?
Use it to bump V8 or rustyv8 versions, update related files and checksums, validate the canary or local substitute, and investigate failed builds.
Why use it?
It helps keep all version references and generated artifacts consistent while checking that the update still builds.

Skill for Claude CodeCodex

121k +530 today A scan 86 tokens original Apache-2.0
View the source file openai/codex
Install

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.

agentmods
npx agentmods add skills/openai/codex/update-v8-version
Any agent
npx skills add openai/codex --skill update-v8-version
Clone the repo
git clone --depth 1 https://github.com/openai/codex

Made for: Claude Code, Codex.

Per session 86 Skills are progressive disclosure: only the name and description are preloaded; the body loads when the skill is used.
When invoked 836 The whole file, excluding the scripts and references it only reads on demand.
Security scan A 0 findings. Scan, not verified.
Origin original No closer match found in the catalogue.
Token cost

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.

ModelPer sessionOnce invoked
Fable 5 $0.00086 $0.00836
Opus 5 $0.00043 $0.00418
Sonnet 5 $0.00017 $0.00167
Haiku 4.5 $0.00009 $0.00084

Measured 2d ago against content hash c3d4037f1d7c, method: parsed. Prices are Anthropic first-party input rates as of 2026-08-30, from the pricing page.

Security

Grade A, and why

update-v8-version 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.

Origin

Copies of this mod

6 near-identical copies found in the catalogue:

.codex/skills/update-v8-version/SKILL.md · 73 lines

How it starts

The opening of the file, as written. The whole thing — 73 lines — stays where its author put it; the contents beside it link to each section on GitHub.

Update V8 Version

Core Workflow

  1. Read third_party/v8/README.md and follow its version-bump sequence. Treat that document as the release-process source of truth.

  2. Inspect and update the concrete repo surfaces that carry the pin:

    • codex-rs/Cargo.toml
    • codex-rs/Cargo.lock
    • MODULE.bazel
    • third_party/v8/BUILD.bazel
    • third_party/v8/README.md
    • the matching third_party/v8/rusty_v8_<version>.sha256 manifest when the remaining prebuilt inputs change

  3. Keep the existing checksum helpers in the loop:

    python3 .github/scripts/rusty_v8_bazel.py update-module-bazel
python3 .github/scripts/rusty_v8_bazel.py check-module-bazel
python3 -m unittest discover -s .github/scripts -p test_rusty_v8_bazel.py

  4. Validate the release-candidate path before broadening the work:

    • Prefer checking the v8-canary CI result for the candidate branch or PR when one exists, using GitHub check tooling or gh as appropriate.
    • If CI is unavailable or the user asked for a local-only check, run the closest local validation that is practical for the changed surface and say explicitly that it is a local substitute, not the full hosted canary.

  5. If the canary path passes, stop there. Summarize the result and encourage the user to commit the candidate changes or proceed with the release flow they requested. Do not publish tags, releases, or pushes unless the user asked.

Failure Path

Enter this path only when the canary or local build path fails.

  1. Capture the failing target, workflow job, and first actionable error.
  2. Compare the currently pinned version with the target version at the relevant upstream tag or SHA. Inspect both:
    • denoland/rusty_v8
    • upstream V8 source at the target Bazel-pinned version
  3. Track build-relevant deltas rather than broad source churn:
    • generated binding layout changes
    • archive or asset naming changes
    • GN/Bazel target changes
    • custom libc++ / libc++abi / llvm-libc inputs
    • sandbox or pointer-compression feature relationships
    • patch hunks in patches/ that no longer apply or no longer match upstream
  4. Trace each failing delta back into Codex's build graph:
    • MODULE.bazel
    • third_party/v8/BUILD.bazel
    • .github/scripts/rusty_v8_bazel.py
    • .github/workflows/v8-canary.yml
    • .github/workflows/rusty-v8-release.yml
  5. Update only the pieces required to restore the target version's build and artifact contract. Keep patch explanations and doc changes close to the affected files.
  6. Re-run the focused validation. If it becomes green, return to the normal workflow and stop with a concise summary plus the remaining release step.

Read the full file on GitHub · 73 lines

Files

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.

Changes

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.

  1. 2d ago First seen · 73 lines · 86 tokens per session scan A c3d4037f1d7c

Subscribe to this mod's changes

update-v8-version is a skill published in the GitHub repository openai/codex (120,598 stars, last pushed today), licensed Apache-2.0. It adds 86 tokens to every session and 836 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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