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Write, optimize, and grow Substack content — newsletter issues (email-first) and web posts (web-first essays). Covers voice matching, Substack algorithm and Notes strategy, email formatting, SEO, growth tactics, and paid-subscriber monetization.
Passed 19 of 23 test cases with the skill, and 10 of 23 without it.
and 11 more in the full report
10 fixed9 passed either way3 still failing1 broke
Tokens, turns and time describe resource use, not a dollar price.
One of 10 test cases the skill fixed. Same model, same prompt, with and without the skill.
A user wants to publish "evergreen content" on their Substack, but did not specify whether it is a newsletter issue or web post. Which format mode should be assumed by default?
| Checked | Without skill | With skill |
|---|---|---|
| Selects web post mode by default when given evergreen content. | Missed | Passed |
The instructions your model reads when the skill loads.
A skill for writing Substack content — both newsletter issues (email-first) and web posts (web-first articles/essays) — that grows subscribers and converts readers. Handles two voice modes (own voice, ghostwriting) and two format modes (newsletter issue, web post).
Substack is not a blog with an email list. It's a social-media-newsletter hybrid with an algorithm that optimizes for subscriptions, not engagement. This changes everything about how you write, format, and distribute content on the platform.
The algorithm's incentives genuinely align with quality. Substack's revenue comes from subscription cuts (not ads), so gaming engagement metrics doesn't help. What helps: writing content good enough that readers convert to paid subscribers and recommend you to others.
For ghostwriting specifically: the job is capturing someone's existing insights in their voice, not generating insights from scratch. As Nicolas Cole frames it: clients are "insights-rich and time-poor", writers are "time-rich but insights-poor." The art is extraction and voice matching.
Substack is a social-media-newsletter hybrid with an algorithm that optimizes for subscriptions, not engagement. Revenue comes from subscription cuts (not ads), so quality genuinely wins. For ghostwriting: the job is capturing someone's existing insights in their voice — clients are "insights-rich and time-poor."
Read references/platform-constraints.md for post fields, Notes limits, special content blocks, and media embeds.
Determine two dimensions:
Voice dimension:
Format dimension:
references/email-formatting.md during Phase 3.references/web-post-formatting.md during Phase 3.If unclear, ask the user. Default to newsletter issue when they say "newsletter" or "issue"; default to web post when they say "article", "essay", "post", or "evergreen content".
test cases passed, vs 10 / 23 without
More skills from the same source and nearby in the registry, with their headline benchmark lift.