write-docs

A writing guide for creating Fern documentation pages from MDX files, plus release notes and changelogs for the Opik project. Fern is the tool that builds the documentation website.

In plain words
What is it for?
Use it when writing or updating Opik documentation, drafting pull-request descriptions, or deciding whether a change belongs in release notes or a changelog.
Why use it?
It removes uncertainty about where pages belong, how to format them, and how to add them to the site's navigation. It also helps keep old documentation links routed to current pages.

Skill for Claude CodeCodex

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/comet-ml/opik/write-docs
Any agent
npx skills add comet-ml/opik --skill write-docs
Clone the repo
git clone --depth 1 https://github.com/comet-ml/opik

Made for: Claude Code, Codex.

Per session 55 Skills are progressive disclosure: only the name and description are preloaded; the body loads when the skill is used.
When invoked 2,855 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 $0.00055 $0.02855
Opus 5 $0.00028 $0.01427
Sonnet 5 $0.00011 $0.00571
Haiku 4.5 $0.00006 $0.00285

Measured 2d ago against content hash 29a98d451e75, method: parsed. Prices are Anthropic first-party input rates as of 2026-08-30, from the pricing page.

Security

Grade A, and why

write-docs 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.

.agents/skills/write-docs/SKILL.md · 287 lines

How it starts

The opening of the file, as written. The whole thing — 287 lines — stays where its author put it; the contents beside it link to each section on GitHub.

Write Docs

The Opik docs site is built with Fern from MDX sources under apps/opik-documentation/documentation/fern/. There is one content surface: fern/docs-v2/. The old v1 surface (fern/docs/) was removed; every v1 URL now redirects to its Opik 2 equivalent through the redirects: list in fern/docs.yml.

Where new pages live

  • Create the file at apps/opik-documentation/documentation/fern/docs-v2/<section>/<page-name>.mdx.
  • Register it in fern/docs.yml under the right section: block in navigation:.
  • Routing is not implied by folder layout. Always check navigation: in fern/docs.yml.

Frontmatter template

Every page uses YAML frontmatter. title and headline are required; the og:* fields are strongly recommended for SEO/social sharing and are present on every page. Do not repeat title as an inline # H1 in the body — Fern renders it from frontmatter.

---
title: Page Title
headline: Page Title | Opik Documentation
og:title: Page Title — Opik
og:description: One-line summary used for social sharing and previews
og:site_name: Opik Documentation
---

subtitle: ... is an optional field used on concept/overview pages to add a secondary line. Landing/overview pages may also set layout: overview.

Style and voice

Pull examples from existing pages when unsure — fern/docs-v2/tracing/advanced/log_traces.mdx, fern/docs-v2/tracing/concepts.mdx, and fern/docs-v2/quickstart.mdx are good anchors.

  • Person: "you" and imperative voice. Professional but approachable.
  • Opening: one or two intro sentences before the first ## heading. No inline H1.
  • Headings: ## for top-level sections, ### for subsections. Never introduce an inline # — that collides with the frontmatter title.
  • Paragraphs: keep them short (2–4 sentences). Mix prose with bullet lists for features, options, and prerequisites.
  • Page shape:
    • Concept pages start with the why, then definitions.
    • How-to pages start with brief context, then the task steps.
    • Overview/landing pages lead with a short pitch and a <CardGroup> of links.
  • End with "## Next steps" linking to 2–4 related pages when useful.

Read the full file on GitHub · 287 lines

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 · 287 lines · 55 tokens per session scan A 29a98d451e75

Subscribe to this mod's changes

write-docs is a skill published in the GitHub repository comet-ml/opik (21,685 stars, last pushed 2d ago), licensed Apache-2.0. It adds 55 tokens to every session and 2,855 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.