Hermoso is a marketing MCP server: 301 tools over one OAuth’d endpoint that let an agent research the ads already running in a market, generate finished image and video ads, publish them, and build the paid campaigns behind them. Codex reaches all of it through one connection. This page is about one slice of that — what Codex can actually do on YouTube, and what YouTube will not let it do.
Connect Hermoso to Codex
- Create an API key. In Hermoso, open Settings → Agents & API keys and press ＋ Create API key. It looks like
hmk_…and carries real spend authority, so treat it like a password. - Add it to
~/.codex/config.toml. Codex reads TOML, not JSON — a copiedmcpServersblock will not load:[mcp_servers.hermoso] url = "https://app.hermoso.ai/mcp" http_headers = { "Authorization" = "Bearer <your key>" } - Ask Codex for something. “Pull my three closest competitors’ longest-running ads and remix the best hook into a 9:16 video,” or “post this render to the channel.” The agent picks the tools; you approve the spend.
The TOML detail is the one that trips people up: every other client in this list takes a JSON mcpServers object, and Codex takes [mcp_servers.<name>] with http_headers.
Then connect YouTube itself, once, under Settings → Connectors in Hermoso. That is an OAuth consent screen, so it is the one step that needs a browser — everything after it is a tool call.
The YouTube tools Codex gets
post_to_youtube— uploads a finished video with a title, a description of up to 5,000 characters, up to 30 tags, and a privacy setting.schedule_post— queues the upload — with the description and tags carried through, which is not something to take for granted.set_youtube_thumbnail— puts a designed thumbnail on the upload. It is the single biggest lever on click-through, and YouTube otherwise picks a frame more or less at random.make_thumbnail— generates that thumbnail in the first place.update_youtube_video / list_youtube_videos— edit an upload’s metadata, or list your own uploads — including unlisted and private ones a public search cannot see.youtube_video_insights / youtube_channel— views, watch time, average view percentage and subscribers gained.list_youtube_comments / reply_to_youtube_comment— read and answer comments as the channel.
The unit really is a video: post_to_youtube takes a videoUrl and there is no image path at all. Two smaller gates worth knowing before an automated upload: a Google project that has not been verified has videos.insert locked to private regardless of what you ask for, and custom thumbnails need a phone-verified channel.
YouTube limits worth knowing before you automate anything
| Text | A YouTube title is capped at 100 characters — and a scheduled item’s text becomes the title. The description is a separate field of up to 5,000 characters, carrying up to 30 tags. It is enforced when the post is created or queued — refused while you are still there to fix it, rather than silently cut on the way out. |
|---|---|
| Visibility | Public, unlisted or private. There is no Studio draft — “YouTube’s API can upload as public, unlisted or private, but it cannot create a Studio draft”, so unlisted is the closest thing to a review state, and it is what an immediate post defaults to so an ad-ready upload is not accidentally public. |
| Carousel | Refused, by name. “YouTube’s unit is a video, not a set of stills. Turn the slides into a video (Hermoso can stitch them) and post that instead, or drop YouTube from this post.” That is not a limitation Hermoso invented to avoid work — it is what YouTube is — and the refusal comes at enqueue, with the way forward attached, rather than as a silently posted first slide. |
| Which account | None — YouTube publishes to the connected channel. |
Try it in Codex
Ask for it in ordinary language — these are sentences, not a DSL:
“Non-interactive: for every mp4 in the input directory, write a title under 100 characters and a 5,000-character description, generate a thumbnail, upload unlisted, print JSON.”
That walks make_thumbnail → post_to_youtube → set_youtube_thumbnail → youtube_video_insights. Interactively Codex shows the call before it runs it. Non-interactively there is nobody to ask, which is worth designing around on any step that publishes or spends.
Codex on YouTube: the part that bites
Upload unlisted from an unattended run, always. YouTube has no Studio draft, unlisted is the review state, and a batch that goes straight to public is a batch you cannot un-publish quietly. Also check the channel first: an unverified Google project has uploads locked to private whatever privacy the job requests, which will look like a bug and is not one.
For unattended runs, prefer the hermoso CLI with --json over the full tool manifest — it is far cheaper in context and easier to assert on.
Research YouTube before you post
search_youtube searches the public YouTube index — which is a different question from “what have I uploaded”, and list_youtube_videos is the tool for that one. For a competitor’s film, analyze_video returns the voiceover, the on-screen text and the beat list with timestamps, which is what you actually want before rebuilding a hook.
The paid half
Hermoso’s Google Ads tools build search, display and Performance Max campaigns — the whole tree in one atomic operation, read back from Google before your agent narrates it — plus Keyword Planner volumes, conversion actions, and sitelinks and callouts created and attached. There is no YouTube video-campaign builder, and it would be wrong to imply one; a YouTube video asset can be uploaded and attached, but the campaign types Hermoso creates are search, display and Performance Max.
What Codex cannot do on its own
An agent with a budget is only useful if the blast radius is bounded, so the fence is in the server rather than in a prompt. Every ad campaign, ad set, ad group and ad is created paused, and the status switches that arm real money refuse to run without an explicit confirmation flag. Every render is quoted first — hermoso_capabilities publishes each model’s exact credit cost before anything spends — and credits are reserved before the first provider call and settled at the exact cost afterwards, so a failed dispatch refunds rather than leaving you billed for nothing. Deletes are confirm-gated too, and every campaign tree is read back from the ad platform before your agent tells you what it built.
One step is deliberately not headless: linking an account is an OAuth consent screen, so you connect the channel once in a browser. Everything after that is a tool call.
The rest of the matrix
From Codex, post to: Facebook · Instagram · Threads · TikTok · X · LinkedIn · Pinterest — or see everything Codex can publish to.
Post to YouTube from: Claude · ChatGPT · Claude Code · Cursor · Cline · OpenClaw · Hermes · Ads from the command line
Frequently asked questions
Can Codex post to YouTube?
Yes, through Hermoso's MCP server. Create an API key in Hermoso under Settings → Agents & API keys, then add https://app.hermoso.ai/mcp to Codex with an Authorization: Bearer header. Codex then has 301 tools, including the ones that publish to YouTube — and the ones that research the ads already running in your market and render the creative in the first place.
How do I connect YouTube to Codex?
Two steps, once each. Create an API key in Hermoso under Settings → Agents & API keys, then add https://app.hermoso.ai/mcp to Codex with an Authorization: Bearer header. Then connect YouTube inside Hermoso under Settings → Connectors, which is an OAuth consent screen in a browser. After that Codex publishes to YouTube as an ordinary tool call.
What is the YouTube caption limit when posting from Codex?
A YouTube title is capped at 100 characters. The description is a separate field of up to 5,000 characters, with up to 30 tags — and a scheduled item’s text becomes the title, so both must be passed explicitly. Hermoso enforces it when the post is created or queued, so Codex is told immediately rather than failing later when nobody is watching.
Can Codex schedule a YouTube post for later?
Yes. schedule_post queues it on one calendar shared with every other channel, with a per-channel caption if the copy should differ, and list_scheduled and cancel_scheduled read and pull it back. YouTube is one of the eight channels that queue.
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