sepia
sepia is an open-source Agent Skill that revises AI-written text, repairing fiction structure and applying venue-specific rules to professional prose.
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Pricing and API checked by an OpenBeat editor on Nov 11, 2026 · facts from the maker’s own site ·
Tool insights
sepia checks and rewrites text that an AI model produced, using a rubric of 30 diagnosis features and rules matched to where the text will be published. It runs inside coding agents such as Claude Code, Codex and Cursor, so writing review happens in the same tool as the rest of the work.
Text from AI models tends to share recognizable habits that make release notes, ticket replies and stories read as machine-made. sepia gives agents a defined way to find those habits and fix them, instead of relying on ad hoc rewriting prompts.
Developers and writers who already work in an Agent Skills-compatible agent and want to clean up AI-drafted fiction, release notes, PR replies, postmortems, tickets or articles. People who want a standalone web editor or a hosted service should look elsewhere, since sepia is a skill package for agents.
What it does
sepia is an Agent Skill by Nanako0129 that revises text written by AI models. It has two main uses. For fiction, it repairs narrative structure before it touches individual words. For professional writing, it applies rules matched to the venue, such as release notes, PR replies, postmortems, tickets and articles.
It works through four operations: write, review, refactor and recreate.
Key features
- A rubric of 30 diagnosis features used to find problems in a draft.
- Fiction narrative-architecture repair that runs before word-level edits.
- Venue-matched rules for release notes, PR replies, postmortems, tickets and articles.
- Per-model fingerprints for text from Claude, GPT, Gemini, DeepSeek and Kimi.
- A sentence length spread check for English and Chinese.
- An optional Hemingway voice profile.
- An opt-in voice-skill interface with persona profiles.
- Native plugin packaging for five agent platforms.
The v0.13.0 release notes list several changes: quoted material is now protected without a declaration, the fiction report gains Discourse and Style scan lines, and the journalism comparison rule is narrowed to unsized figures. The refactor operation also records missing verdicts on a Deferred line.
Pricing
sepia is open source under the MIT license, and the free plan is the whole product. As of November 2026 the maker's site lists no paid plans and no starting price. Your own agent and the model behind it may carry their own costs, which are not described in the facts for sepia.
API and integrations
No API is stated on the maker's site, and no SDKs are listed. sepia installs as a skill. Native platforms are Claude Code, Codex, Grok Build, Antigravity and QwenPaw. Through the Skills CLI it reaches Agent Skills-compatible agents, with 77+ mentioned. Listed integrations also include Cursor, Cline, Windsurf, Copilot, OpenCode and goose.
Good to know
- The maintainer has not exercised runtime behavior outside the five native platforms.
- The voice-skills interface rests on one blind review experiment.
- Standalone wrapper installation is unsupported. Install the complete plugin package.
- QwenPaw installation needs a git clone. Zip installs register nothing.
- The founding date is not stated on the maker's site.
- Documentation is the GitHub readme, and release notes are on the GitHub releases page.
FAQ
Is sepia free?
Yes. sepia is open source under the MIT license, and as of November 2026 no paid plans or prices are stated on the maker's site. Costs from the agent or model you run it in are separate.
Which agents does sepia work with?
sepia has native plugin packaging for Claude Code, Codex, Grok Build, Antigravity and QwenPaw. It also lists Cursor, Cline, Windsurf, Copilot, OpenCode and goose, and the Skills CLI reaches 77+ Agent Skills-compatible agents. The maintainer says runtime behavior outside the five native platforms has not been exercised.
What kinds of text can sepia revise?
It handles fiction, where it repairs narrative structure before word-level edits. It also handles professional writing with rules for release notes, PR replies, postmortems, tickets and articles.
Does sepia have an API?
An API is not stated on the maker's site, and no SDKs are listed. sepia is used as an Agent Skill installed in a compatible coding agent.
Which AI models does sepia recognize?
It includes per-model fingerprints for text from Claude, GPT, Gemini, DeepSeek and Kimi. These help diagnose habits typical of each model's output.
Releases
No tracked releases yet.
In the news
No coverage yet.