Reddit Post

Posting to Reddit from an agent

Reddit writes fail for agents in ways that look like bugs but aren't. The naive approaches — a scripted HTTP client, or Playwright/Puppeteer launching its own browser — hit walls no amount of retry logic fixes. Understanding why saves a long debugging spiral.

The architecture, and why

rdtx attaches over CDP to a Chrome the human launched, and issues writes as same-origin fetch calls from inside the logged-in page. Three measured facts make that the right shape; references/browser-session.md has the evidence.

The automation flag is set at launch, not by attaching. Puppeteer and Playwright pass --enable-automation, setting navigator.webdriver = true. Start Chrome with only --remote-debugging-port and attach afterwards, and it stays false.

"Prove your humanity" is transient. It's a JS proof-of-work that self-resolves in seconds, not a block. rdtx polls through it. Concluding you've been blocked is the most common way to abandon a working setup.

Let the page build the request. Writes reuse Reddit's own cookies and CSRF material verbatim, so there's no auth protocol to reimplement or keep in sync.

Setup, once

Live commands require Node.js 18+, agent-browser, and the user's own logged-in Chrome profile; see references/browser-session.md. The synthetic verifier needs only Node.js 18+.

node scripts/rdtx.mjs launch    # Chrome with a debug port, no automation flags
node scripts/rdtx.mjs login     # the human logs in by hand
node scripts/rdtx.mjs doctor    # cdp / challenge / login, reported separately

rdtx never handles the password. doctor reports each layer independently, so a failure tells you which one broke.

Verify the installed runtime without Reddit

Run node scripts/verify-synthetic.mjs with no arguments. It starts the production submit CLI without --yes, checks the real temporary audit entry and both remote_checks, and arms guards that fail if the CLI tries to reach a network or agent-browser. It also exercises the other shared Reddit contracts with fabricated fixtures. A pass proves the local dry-run boundary only; it does not authorize or prove a real Reddit write. Overall passed is the AND of all five shared checks; inspect functional.reddit_post for this skill's evidence.

An independent tester can submit the exact named verifier result through the structured installed-run report. Select the reddit-post zero-input synthetic option only after running the installed copy. This proves installation and local contract behavior, not a live Reddit write.

Commands

Every write is a dry run unless you pass --yes

node scripts/rdtx.mjs submit test "My title" --text "Body"        # prints a plan, posts nothing
node scripts/rdtx.mjs submit test "My title" --text "Body" --yes  # actually posts

An agent composing a post will often run the command just to inspect the payload. A tool that posts on first invocation turns that into a public, hard-to-undo action. The dry run returns the requested payload so the subreddit, title, body, URL, and requested flair can be confirmed before anything leaves the machine. It is fully local: no browser command or Reddit request is made, and both entries in plan.remote_checks report not_run. Both dry runs and real writes append to ~/.rdtx/audit.jsonl with executed: true|false.

Flair is required in most large subreddits

node scripts/rdtx.mjs submit ClaudeAI "Title" --text "Body" --flair "Skills" --yes

After explicit --yes confirmation, submit resolves flair by name and checks is_flair_required before the write request, so a missing flair fails before Reddit creates a post. A wrong name returns the subreddit's actual flair list. The default dry run deliberately does not perform either remote check; it reports the requested flair for review instead.

A 200 is not proof — this is the part people miss

Large subreddits route new posts through AutoMod, where they sit reachable by direct link but absent from listings and marked non-indexable. The write returns 200 and reads back perfectly.

Measured on a real post, minutes apart, before and after a moderator approved it:

removed_by_category: "automod_filtered"   →   null
is_robot_indexable:  false                →   true

submit re-reads after writing and reports the result:

"visibility": { "state": "automod_filtered", "public": false, "indexable": false }

States are live, automod_filtered, not_indexable, removed. Treat anything other than live as not published yet, and wait rather than reposting — reposting to escape a filter converts one filtered post into a spam pattern across the account. Pass --no-verify to skip the check.

Image posts

Image upload works, but only through a trusted path. Two things had to be true, and both were found by failing first:

Synthetic events are ignored. Setting input.files from page JavaScript sticks on the element and shreddit's Lit component never reacts; a dispatched DragEvent is ignored the same way. The API route is closed too — /api/media/asset.json 403s under modhash, X-CSRF-Token, a csrf_token field, and all combinations. What works is DOM.setFileInputFiles over CDP, which the page cannot distinguish from a human choosing a file.

Most of the file inputs are decoys. The composer keeps ~7 mounted at once as placeholders for the other post types, and setFileInputFiles succeeds silently against the inert ones — the command returning is not evidence of anything. Only the input with accept="image/*" actually holds the file. image-post.mjs sweeps every candidate and keeps whichever ends up non-empty.

# stage everything, submit nothing (default)
node scripts/image-post.mjs test "My title" --image ./a.png,./b.png

# actually post
node scripts/image-post.mjs test "My title" --image ./a.png --flair "Skill Share" --yes

Title goes in via Input.insertText after a real Input.dispatchMouseEvent click, and Post is clicked at its measured coordinates — all trusted, all through Reddit's own composer, so there is no write protocol to reimplement.

Gotcha: Reddit persists composer drafts. Images staged in an earlier session are still there when you navigate back, so a post can go out with more images than you passed. Check the returned n against what you supplied, or clear the draft first.

Image link posts remain available and need none of this — submit --url <image-url> renders with a preview.

Choosing a target when testing

Use r/test or the user's own profile subreddit (u_<username>). Both exist for this and affect no community. Proving a setup against a real topical subreddit spends the user's account standing on a smoke test.

Pacing

A jittered ~2.3–8s wait precedes each write, keeping you inside Reddit's rate limits. For many writes, spread them out rather than removing the pacing — Reddit's "You are doing that too much" costs more time than the waits.

Scope

One account — the user's own. No multi-account, proxy-rotation, or fingerprint-spoofing support, and none is planned: that targets platform integrity detection rather than getting your own posting to work, and Reddit's terms prohibit it. If a task seems to need several accounts looking like unrelated people, raise it with the user rather than engineering around it.

Troubleshooting

Related

• reddit-seo — audit whether existing posts are indexable
• reddit-archive — capture a post with its media