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Agent skill

Deliverability Optimization

by revfactory in revfactory/harness-100

Email deliverability optimization skill used by the Editor-in-Chief and analyst agents.

Apache-2.0Auto-check passedBackend & APIs

Install Deliverability Optimization

skills CLI
$ npx skills add revfactory/harness-100 --skill deliverability-optimization -a claude-code

Project install by default; add -g for ~/.claude/skills/.

GitHub CLI
$ gh skill install revfactory/harness-100 deliverability-optimization --agent claude-code

Project scope by default; add --scope user for a personal install. Needs GitHub CLI 2.90.0 or later (public preview).

Manual copy
$ git clone --depth 1 https://github.com/revfactory/harness-100.git skills-src && mkdir -p .claude/skills && cp -r skills-src/en/03-newsletter-engine/.claude/skills/deliverability-optimization .claude/skills/deliverability-optimization && rm -rf skills-src

Use ~/.claude/skills/ instead of .claude/skills for a personal install. The folder must contain SKILL.md.

Claude Code skills documentation · loads skills from .claude/skills/

Facts

Skill name
deliverability-optimization
GitHub stars
1.3k
Token cost
~1.1k tokens
SKILL.md length
481 words
Files
1
Skills in repo
464
Repo updated
First seen
Licence
Apache-2.0

At a glance

Email deliverability optimization skill used by the Editor-in-Chief and analyst agents.

  • Works in 5 steps: Image-to-text ratio: Keep images at 40%… → Link count: 5–7 per email is optimal;… → Shortened URLs: Shortened URLs (bit.ly,… → …
  • Email authentication
  • SKILL.md covers Why Deliverability Matters, Spam Filter Trigger Avoidance…, Email Client Rendering Checks and Legal Compliance Checklist, plus 1 more section
  • Instructions only: no scripts, shell commands, URLs or credentials in SKILL.md

What it does

Deliverability Optimization is an agent skill from revfactory/harness-100. Email deliverability optimization skill used by the Editor-in-Chief and analyst agents. Provides spam filter avoidance, technical authentication, content filtering rules, and list hygiene management methodologies. Use for 'deliverability,' 'spam filters,' 'email authentication,' 'send optimization,' and similar requests.

Its SKILL.md is about 1.1k tokens, which your agent loads only when the skill is triggered. It is a single SKILL.md file with no bundled scripts.

It sits in Backend & APIs, covering Transactional email. The licence is Apache-2.0.

When your agent uses it

  • Email authentication
  • Send optimization
  • Similar requests

Example prompts

  • “deliverability,”
  • “spam filters,”
  • “email authentication,”
  • “/deliverability-optimization”

Workflow steps

5 steps, taken from the first numbered list in SKILL.md.

  1. Image-to-text ratio: Keep images at 40% or less, text at 60% or more
  2. Link count: 5–7 per email is optimal; 15+ risks spam classification
  3. Shortened URLs: Shortened URLs (bit.ly, etc.) trigger spam filters — use original URLs
  4. HTML code quality: No broken tags or excessive inline styles
  5. Unsubscribe link: Must be clearly included at the bottom (legal obligation + spam prevention)

What it can do on your machine

Read from SKILL.md and the folder at commit 8e8d35c. It shows what the files ask for, not the result of running them.

  • Tool permissions

    Pre-approves nothing: there is no allowed-tools line, so your agent's usual permission prompts apply.

    From allowed-tools in the SKILL.md frontmatter.

  • Runs code

    No scripts in the folder and no shell commands in SKILL.md.

    From the folder's file list and the shell code blocks in SKILL.md.

  • Network

    No URLs in SKILL.md.

    From URLs in SKILL.md, links to its own repository left out.

  • Credentials

    Names no API keys, tokens, secrets or passwords.

    From names ending in _API_KEY, _TOKEN, _SECRET, _KEY or _PASSWORD in SKILL.md.

Context cost

Deliverability Optimization loads about 1.1k tokens when it runs. Until then it costs about 88 tokens; SKILL.md has 481 words of instructions outside code blocks.

Always · name and description, kept in context so the agent knows when to use it
~88
When it runs · the whole SKILL.md, loaded when a task matches
~1.1k

Estimates: characters ÷ 4, the usual rule of thumb; real counts depend on the model's tokenizer. Scripts and assets cost tokens only if the agent reads them.

Safety

Auto-check passed

The automated check found no risky patterns in SKILL.md.

Automated static check — not a guarantee. Review scripts before installing. It scans the text of SKILL.md for risky patterns (piping downloads into a shell, reading credential files, hidden Unicode, destructive commands); files beside SKILL.md are not scanned.

SKILL.md

The full file from revfactory/harness-100 at commit 8e8d35c, republished under its Apache-2.0 licence (© revfactory). 481 words, ~1,094 tokens.

Download SKILL.mdSave it as .claude/skills/deliverability-optimization/SKILL.md (or your agent's skills folder).
name
deliverability-optimization
description
Email deliverability optimization skill used by the Editor-in-Chief and analyst agents. Provides spam filter avoidance, technical authentication, content filtering rules, and list hygiene management methodologies. Use for 'deliverability,' 'spam filters,' 'email authentication,' 'send optimization,' and similar requests.

Deliverability Optimization — Email Deliverability Optimization Methodology

Technical deliverability expertise used by the editor-in-chief and analyst agents when designing final edits and send strategies.

Why Deliverability Matters

No matter how perfect your newsletter is, if it doesn't reach the inbox, all effort is wasted. On average, 15–20% of emails land in spam folders or promotional tabs.

Spam Filter Trigger Avoidance Guide

Subject Line Spam Trigger Words
Risk LevelWord/PatternAlternative
HighFree, FREE, 100% off, Winner"Complimentary," "Gift," "Special offer"
High!!!, ???, ALL CAPSOne exclamation max, sentence case
MediumAct now, Urgent, Deadline"By this week," "Limited time"
MediumClick here, Click now"Check it out," "Take a look"
LowRe:, Fwd: (fake reply/forward)Absolutely prohibited — destroys trust
Body Content Filtering Rules
  1. Image-to-text ratio: Keep images at 40% or less, text at 60% or more
  2. Link count: 5–7 per email is optimal; 15+ risks spam classification
  3. Shortened URLs: Shortened URLs (bit.ly, etc.) trigger spam filters — use original URLs
  4. HTML code quality: No broken tags or excessive inline styles
  5. Unsubscribe link: Must be clearly included at the bottom (legal obligation + spam prevention)
Sender Reputation Management
FactorOptimal StateManagement Method
Bounce RateBelow 2%Remove hard bounces immediately, soft bounces after 3
Spam Complaint RateBelow 0.01%Maintain content quality, make unsubscribing easy
AuthenticationSPF + DKIM + DMARC configuredCoordinate with domain administrator
Dedicated IPWhen sending 100K+/monthShared IPs are affected by others' reputation
IP Warm-upGradual increase over 2–4 weeks for new IPsDay 1: 50 emails → double daily → target volume

Email Client Rendering Checks

Rendering issues that must be verified during newsletter editing:

ClientConsiderations
GmailPrevent Promotions tab classification — reduce images, increase text, use personal tone
OutlookLimited CSS support — avoid complex layouts, use table-based layouts
Apple MailDark mode support — use transparent background images, test color inversion
All MobileSingle-column layout, buttons minimum 44x44px, font 14px+
Show full SKILL.md (168 more words)Show less
Gmail Promotions Tab Avoidance Strategy
  1. Personal tone: "Hi [Name]" — minimize marketing-speak
  2. Minimize images: Text-centric, limit to 1–2 images
  3. Minimize links: Keep to 2–3 essential links only
  4. Encourage replies: "Reply to this email" — signals two-way communication
  5. Sender name: Personal name over brand name (e.g., "Jane from [Newsletter Name]")

Legal requirements that must be verified when publishing a newsletter:

CAN-SPAM (US)
  • Physical mailing address included
  • Unsubscribe processed within 10 business days
  • No deceptive subject lines
GDPR (EU)
  • Explicit consent (no pre-checked boxes)
  • Data processing purpose stated
  • Data deletion request handling system
  • Privacy policy link
CASL (Canada)
  • Express or implied consent obtained
  • Sender identification included
  • Unsubscribe mechanism provided

Editor-in-Chief's Pre-Send Checklist

#ItemCheck
1No spam trigger words in subject line[ ]
2Preheader text configured[ ]
3All links verified working[ ]
4Image alt text entered[ ]
5Mobile rendering tested[ ]
6Unsubscribe link working[ ]
7Sender information accurate[ ]
8A/B test setup confirmed[ ]
9Send time optimized per segment[ ]
10Test send → receipt confirmed[ ]

© revfactory, Apache-2.0. Rendered from Markdown: HTML in the file is shown as text, images as links, and headings moved down two levels. Raw file

Files

Just SKILL.md in en/03-newsletter-engine/.claude/skills/deliverability-optimization of revfactory/harness-100.

Open the folder on GitHubat commit 8e8d35c

Compare with similar skills

Deliverability Optimization next to the 5 skills that share the most tags, products or categories with it. Stars are the repository's; “used in” counts other GitHub owners with a copy.

Deliverability Optimization compared with similar skills
SkillStarsUsed inTokensAuto-checkLicenceRepo updated
Deliverability Optimization this skillrevfactory/harness-1001.3k—~1.1kAutomated safety check: PassApache-2.0
Stripe Projectsfossasia/eventyay1.7k5 repos~2kAutomated safety check: NotesApache-2.0
WooCommerce Email Editor Developmentwoocommerce/woocommerce11k—~893Automated safety check: PassCustom licence
Email Best Practicesviclafouch/meme-studio1107 repos~787Automated safety check: PassNone
React Emailviclafouch/meme-studio1102 repos~3.6kAutomated safety check: PassMIT
Email Deliverability Auditgrowthenginenowoslawski/coldoutboundskills740—~3.4kAutomated safety check: PassMIT

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Categories

Questions about Deliverability Optimization

What does Deliverability Optimization do?

Email deliverability optimization skill used by the Editor-in-Chief and analyst agents. Deliverability Optimization is an agent skill from revfactory/harness-100. Email deliverability optimization skill used by the Editor-in-Chief and analyst agents.

When should I use Deliverability Optimization?

Deliverability Optimization fits situations like: email authentication; send optimization; similar requests.

How do I install Deliverability Optimization in Claude Code?

Run `npx skills add revfactory/harness-100 --skill deliverability-optimization -a claude-code`. Or copy the skill folder (en/03-newsletter-engine/.claude/skills/deliverability-optimization in revfactory/harness-100) into .claude/skills/deliverability-optimization in your project. Claude Code loads it when a task matches its description.

How do I install Deliverability Optimization in Codex?

Run `npx skills add revfactory/harness-100 --skill deliverability-optimization -a codex`. Or copy the skill folder (en/03-newsletter-engine/.claude/skills/deliverability-optimization in revfactory/harness-100) into .agents/skills/deliverability-optimization in your project. Codex loads it when a task matches its description.

Can I use Deliverability Optimization in Cursor, Gemini CLI or GitHub Copilot?

Cursor, Gemini CLI, GitHub Copilot and OpenCode also load SKILL.md folders. With the skills CLI, run `npx skills add revfactory/harness-100 --skill deliverability-optimization -a cursor` (or -a gemini-cli, github-copilot or opencode for the others). To copy it by hand, put the folder in .cursor/skills/deliverability-optimization, .gemini/skills/deliverability-optimization, .github/skills/deliverability-optimization and .opencode/skills/deliverability-optimization in your project.

What does Deliverability Optimization need to run?

SKILL.md names no scripts, command-line tools or credentials: Deliverability Optimization is instructions for the agent only.

Does Deliverability Optimization access the network?

SKILL.md contains no URLs. Any network use would come from the scripts or tools the agent runs. This is read from the text; nothing was executed.

Is Deliverability Optimization safe to install?

Our automated static check of SKILL.md found no risky patterns, such as piping downloads into a shell, reading credential files or hidden Unicode. It is not a guarantee. Review the folder before installing.

What licence does Deliverability Optimization use?

Deliverability Optimization is published under the Apache-2.0 licence (the repository's licence). It allows redistribution, so the full SKILL.md is shown on this page.

How many tokens does Deliverability Optimization use?

About 1.1k tokens (SKILL.md is roughly 4.4k characters). Agents keep only the skill's name and description in context until a task matches; then they load SKILL.md in full.

What are the alternatives to Deliverability Optimization?

Skills that share tags, products or a category with Deliverability Optimization: Stripe Projects (fossasia/eventyay, 1.7k stars), WooCommerce Email Editor Development (woocommerce/woocommerce, 11k stars), Email Best Practices (viclafouch/meme-studio, 110 stars) and React Email (viclafouch/meme-studio, 110 stars). The comparison table on this page puts their stars, adoption, token cost, safety result and licence side by side.

Who maintains Deliverability Optimization?

revfactory (a GitHub user) maintains it in revfactory/harness-100, which has 1,290 GitHub stars. The repository holds 464 skills in this directory. The repository was last updated on March 22, 2026.

Source: revfactory/harness-100 on GitHub. Facts on this page come from the repository at the commit we read; the author's words are quoted as theirs.