MELLOW HUB · FIELD NOTES

Unified social media APIs compared: billing, MCP and agent controls

Ayrshare, Zernio, Upload-Post, Outstand, Blotato, Postiz, Buffer and Mellow Hub compared on billing, networks, MCP, write safety and agent controls.

By Mellow · Updated September 24, 2026

The short answer

No single API fits every job. All eight services here publish to the major networks through one API and a hosted MCP server, so the differences that decide a choice are elsewhere: what the bill counts (profiles, accounts, channels, posts or a flat plan), which networks the publishing endpoint accepts, whether a retried request can post twice, and how narrowly you can limit what an AI agent publishes on its own.

For one realistic workload, three brands with 15 accounts and 180 deliveries a month, published list prices run from $19 (Outstand) to $299 (Ayrshare) a month; Mellow Hub’s Studio plan is $49. Blotato publishes to 9 networks, Mellow Hub to 9 and Outstand to 12, while Postiz lists 32 platform types. Mellow Hub is the only one of the eight that requires an idempotency key on every post; Ayrshare, Outstand, Upload-Post and Zernio offer one, and Buffer’s and Blotato’s docs say they have none.

Disclosure: Mellow publishes this page and makes Mellow Hub. Hub’s rows are generated from its own code and pricing configuration. Every other cell links to the vendor’s own page, checked 24 September 2026; third-party reviews were not used. Where a vendor’s public pages do not say something, the table says “not stated”: the feature may exist, but it is not documented where we looked.

How the services were compared

Eight services that publish to several social networks through one API and run an MCP server for AI agents: Ayrshare, Blotato, Buffer, Mellow Hub, Outstand, Postiz, Upload-Post and Zernio (formerly Late). Seven criteria:

Billing unit. What makes the bill grow: a profile (a brand or client grouping several networks), a connected account or channel, each post delivered to one account, or a flat plan with caps.
Networks. The platforms the publishing endpoint accepts, counted the way the vendor counts them, with notable gaps among Instagram, TikTok, YouTube, Facebook, LinkedIn, X, Threads, Pinterest, Bluesky, Reddit and Google Business Profile.
MCP server. Whether the vendor hosts one, and how an agent signs in: OAuth, with dynamic client registration where the docs say so, or an API key.
Write safety. Idempotency keys, which make a retried request return the original post instead of publishing a second one, and validation before anything is sent.
Agent delegation controls. A review or approval step, daily limits the owner sets, key scopes and expiry, and an audit log of what an agent did.
Free tier. What you can do without paying, and the length of any trial.
Starting paid price. The cheapest self-serve plan, billed monthly, in USD before tax.

Rows are alphabetical. The page does not rank the services: which one fits depends on the workload, and the section on choosing says when each is the better pick, including instead of Hub.

Billing unit, free tier and starting price

Checked 24 September 2026 on each vendor’s public pages. Monthly billing, USD, before tax.
Service	Billing unit	Free tier	Starting paid price
Ayrshare	Per social profile: one customer, brand or location, with any number of networks. Source: pricing	No free plan for new sign-ups; the old Basic plan is closed. A 28-day trial of Launch, no card required. Sources: pricing FAQ, Basic plan note	Premium $149 for one profile and one user; several client profiles from Launch at $299 (up to 10). Source: pricing
Blotato	Flat plans with caps on connected accounts, AI credits and queued posts; no per-post fee. Source: rate card	No free plan. A 7-day trial with a card that excludes the API and MCP; creating an API key starts the paid plan. Source: rate card	Starter $29: 20 connected accounts, 1,250 AI credits. Source: pricing
Buffer	Per connected channel, cheaper per channel as you add more. Source: pricing	Free plan: 3 channels, 10 scheduled posts per channel, 1 API key and 3,000 API requests a month. Source: pricing	Essentials $6 per channel for the first 10, then $4; Team, with approvals, $12 per channel for the first 10. Source: pricing
Mellow Hub	Brand profiles plus a monthly allowance of publications shared across them; one post delivered to one account is one publication. Source: pricing	No free publishing. Connecting accounts, drafts and `validate_post` cost nothing; a 7-day trial with a card for eligible new subscribers. Source: pricing	Solo $19: 1 profile and 150 publications a month. Source: pricing
Outstand	Per post delivered to one connected account; accounts and seats are free. Drafts are not billed; failed deliveries are. Source: pricing	None: its pricing page says there is no permanently free tier. Source: pricing	$19 including 3,000 posts; then $0.007 a post to 10,000 and $0.005 above. Source: pricing
Postiz	Hosted: plans by number of connected channels, unlimited posts. Self-hosted: no plan limits. Sources: plans, cloud vs self-hosted	Hosted: no free plan, a 7-day trial. Self-hosted: open source under AGPL-3.0, no licence fee. Sources: cloud vs self-hosted, repository	Standard $29: 5 channels. Source: pricing
Upload-Post	Plans by number of profiles; a profile is one person or client with one account per network. Unlimited uploads on paid plans. Source: pricing	Free plan: 10 uploads a month on 2 profiles, no card; TikTok is not included. Sources: pricing, plan table	Basic $24 a month for 5 profiles, or $16 a month billed yearly. Sources: pricing, plan table
Zernio	Per connected account, in graduated bands, prorated by the day; profiles are free. Source: pricing	The first 2 connected accounts, with unlimited posts; no card required. Source: pricing	$6 per account for accounts 3 to 10, $3 for 11 to 100, $1 after that. Source: pricing

Networks and MCP servers

Checked 24 September 2026 on each vendor’s public pages. Network counts are the vendors’ own.
Service	Networks for publishing	MCP server and sign-in
Ayrshare	13 in its publishing docs (its site says 14+): adds Reddit, Google Business Profile, Snapchat and Telegram to the nine Hub covers. Since 31 March 2026, posting to X needs your own X developer credentials. Sources: networks, MCP setup	Hosted, Streamable HTTP, at `api.ayrshare.com/mcp`. API key in a header only; its docs say it publishes no OAuth metadata, so personal claude.ai and Claude Desktop connectors cannot sign in. Source: MCP setup
Blotato	9: Instagram, TikTok, LinkedIn, Facebook, X, Threads, Bluesky, Pinterest and YouTube, the same nine as Hub. No Reddit or Google Business Profile. Source: rate card	Hosted, Streamable HTTP, at `mcp.blotato.com/mcp`. OAuth sign-in in supported clients, or an API key. Source: access docs
Buffer	11 plus its own Start Page: Instagram, Facebook, X, LinkedIn, Pinterest, YouTube (Shorts), TikTok, Threads, Bluesky, Mastodon and Google Business Profile. No Reddit. Sources: MCP guide, channel table	Hosted at `mcp.buffer.com/mcp`. OAuth through connectors such as Claude and Claude Code, or an API key as a Bearer token. Sources: MCP guide, Claude guide
Mellow Hub	9: Instagram, TikTok, YouTube, X, LinkedIn, Threads, Bluesky, Pinterest, Facebook. TikTok connects as a personal or a Business account. No Reddit, Google Business Profile, Telegram, Discord, Slack, Mastodon or Snapchat. Source: network rules	Hosted, Streamable HTTP, at `https://www.mellow.world/mcp`. OAuth 2.1 with dynamic client registration and PKCE, or an API key the owner creates. Source: MCP guide
Outstand	12: X, LinkedIn, Instagram, TikTok, Facebook, Threads, Bluesky, YouTube, Pinterest, Google Business Profile, Vimeo and Reddit. X, Google Business Profile, Vimeo and Reddit need your own developer app. Source: facts	Hosted at `mcp.outstand.so/mcp`. OAuth sign-in in which you pick one organization, or an API key. Source: MCP setup
Postiz	32 platform types in its API docs, counting variants such as a LinkedIn profile and page; includes Reddit, Google My Business, Telegram, Discord, Mastodon and blogs. Self-hosting needs your own developer app for most networks, including Instagram, TikTok, YouTube, X and LinkedIn. Sources: API docs, self-host providers	Hosted at `mcp.postiz.com`, with an OAuth sign-in link, or an API key as a Bearer token or in the URL; a self-hosted instance serves its own. Sources: MCP page, MCP docs
Upload-Post	22 destinations including blogs and newsletters; the social ones include Reddit, Google Business Profile, Discord, Telegram and Mastodon. Its docs currently answer Reddit uploads with HTTP 503. Sources: platform list, upload docs	Hosted at `mcp.upload-post.com/mcp`, open source under MIT. An API key, or OAuth 2.1 with dynamic client registration and PKCE. Source: MCP docs
Zernio	16, including Reddit, Google Business Profile, Telegram, WhatsApp, Discord and Slack; Snapchat is in closed beta. X API calls are passed through at X’s own rates. Sources: platforms, pricing	Hosted at `mcp.zernio.com/mcp`. OAuth 2.1 with PKCE and open dynamic client registration, or an API key; also a local stdio server. Source: MCP setup

Write safety and agent delegation controls

Checked 24 September 2026 on each vendor’s public pages. “Not stated” means not found in the public docs, not absent.
Service	Write safety	Agent delegation controls
Ayrshare	Optional `idempotencyKey`: a repeated key is rejected, though simultaneous duplicates may get through. Similar content within two days is blocked. A `validate_post` dry run over MCP; scheduled posts are pre-validated by default. Sources: idempotency, duplicates, MCP tools, post API	`requiresApproval` holds a post until it is approved through the API; its Claude Code plugin asks before each publish. Key scopes, key expiry, owner-set daily caps and an audit log: not stated. Sources: approval workflow, Claude Code plugin
Blotato	Its docs say no idempotency header is documented for creating posts. Media is validated for each destination platform. Sources: errors and retries, media	Blotato’s own per-network daily caps, such as 50 Instagram posts per account in 24 hours. Tool approval is left to the AI client. Key scopes, expiry and an audit log: not stated. Sources: facts, MCP FAQs
Buffer	Its docs say write tools take no idempotency key, so a retried create can publish twice. The CLI’s `--dry-run` validates input locally. Sources: efficient usage, CLI	Approval workflows and access levels on the Team plan. An API key reaches every organization in the account, with no narrower scope; requests are capped per plan, e.g. 250 a day on Free and Essentials. Audit log: not stated. Sources: pricing, authentication, rate limits
Mellow Hub	An idempotency key is required on every post: a retry returns the original, and a key reused for different content is refused. `validate_post` is free, publishes nothing and reports every problem per channel; the same checks run before anything is sent. Source: API and MCP reference	Each key or OAuth grant carries its channels, review or autopilot, a daily ceiling of 1 to 1,000 posts and an expiry (up to 30 days for OAuth grants). Posts, refusals, approvals and cancellations are journaled in Agents; revocation applies on the next request. A key cannot create keys or approve its own post. Source: MCP guide
Outstand	Optional `Idempotency-Key` on post creation, replayed for 24 hours. Requests are validated, for example against each network’s character limit. Sources: idempotency, create a post	OAuth access is limited to one organization and revocable. API keys are unscoped within the organization and do not expire, but revoke immediately and cannot create keys. A usage-limits endpoint is marked “coming soon”. Approval step and audit log: not stated. Sources: MCP setup, usage limits
Postiz	Posts are validated against every selected channel, and again on the server. Idempotency key: not stated. Sources: validation, API docs	Preview links collect client comments, but its docs say no approved state blocks publishing. API keys do not expire and are revoked by rotating; OAuth apps can be revoked. Per-agent daily caps, key scopes and an audit log: not stated. Sources: approvals, developer settings
Upload-Post	Optional `Idempotency-Key`: a retry returns the existing job instead of a duplicate. Payload sizes are validated before sending where limits are known. Dry-run endpoint: not stated. Sources: upload docs, limits	OAuth connectors can be revoked in Connected Apps. Approval step, owner-set daily caps, key scopes or expiry and an audit log: not stated. Sources: MCP docs, authentication
Zernio	`x-request-id` returns the original post for about five minutes; identical content to the same account within 24 hours is rejected. A dry-run post validation endpoint. Sources: idempotency, validate post	API keys can be limited to profiles, made read-only, denied resource groups and set to expire; team roles include a read-only Viewer; team-management changes are audit-logged. Its docs say OAuth connectors currently act with full access. Approval step: not stated. Sources: create key, security

Notes on each service

Ayrshare

Ayrshare covers publishing, post history, analytics, comments and direct messages through one API, and bills by profile, so a brand on ten networks is one profile (pricing). Its MCP server takes only an API key in a header; its docs say personal claude.ai and Claude Desktop connectors cannot sign in, and that posting to X has needed your own X developer credentials since 31 March 2026 (MCP setup).

Blotato

Blotato pairs content creation, meaning AI images, video and voiceovers, with an API and MCP server for the same nine networks Hub covers, on flat plans with no per-post fee (rate card). Its trial excludes the API and MCP, so an agent build starts on the paid Starter plan, and its docs state that no idempotency header is documented for creating posts (errors and retries).

Buffer

Buffer’s public API is a GraphQL API with API keys, OAuth with PKCE for apps, and a hosted MCP server (authentication, MCP guide). Pricing is per channel with a free plan for three channels, and approval workflows need Team (pricing). Its docs say that write tools take no idempotency key, and API volume is capped per plan (efficient usage, rate limits).

Mellow Hub

Hub is built for delegating publishing to an agent: each API key or OAuth grant carries its channels, review or autopilot mode, a daily ceiling and an expiry, actions are journaled in Agents, and revocation applies on the next request. Idempotency keys are required and validate_post is free. Plans: Solo $19 a month for 1 profile and 150 publications; Studio $49 a month for 3 profiles and 600 publications; Scale $99 a month for 10 profiles and 1,500 publications, each with monthly AI credits for Studio carousels and covers (Solo 300, Studio 750, Scale 1,500). Pricing.

Outstand

Outstand bills per post delivered to an account, so adding accounts or teammates does not change the bill, and $19 covers 3,000 posts a month (pricing). It supports idempotency keys on post creation and an OAuth MCP sign-in scoped to one organization; four networks, X, Google Business Profile, Vimeo and Reddit, need your own developer app (idempotency, facts).

Postiz

Postiz is open source under AGPL-3.0 and can be self-hosted, or used hosted from $29 a month by channel count (repository, plans). It has the longest platform list here, including communities and blogs. Self-hosting means registering your own developer apps for most networks, and its docs describe client approval as a conversation, not a state that blocks publishing (self-host providers, approvals).

Upload-Post

Upload-Post sells plans by profile, with unlimited uploads on paid plans, a free tier of 10 uploads a month and an FFmpeg video-processing API in the same account (pricing). Its MCP server is open source under MIT and supports OAuth with dynamic client registration; its docs currently answer Reddit uploads with HTTP 503 (MCP docs, upload docs).

Zernio, formerly Late

Zernio is the new name of Late; getlate.dev now redirects to zernio.com (rebrand). It charges per connected account with the first two free, covers 16 posting platforms plus inbox, ads, WhatsApp and SMS, and lets you restrict API keys by profile, read-only access, resource group and expiry, although its docs say OAuth connectors currently act with full access (pricing, API keys).

When to choose which

Choose Outstand instead of Hub when you publish modest volumes across many accounts: $19 covers 3,000 posts with no charge per account, and retries are protected by idempotency keys.
Choose Upload-Post instead of Hub when you want a low fixed price for many profiles with unlimited uploads, a free tier to prototype on, or video processing in the same API.
Choose Zernio instead of Hub when you need networks Hub does not cover, such as Reddit, Google Business Profile, Telegram, WhatsApp, Discord or Slack, inbox and ads APIs, or two free accounts to start.
Choose Ayrshare instead of Hub when you embed social features for many customers and need comments, direct messages, post history and account analytics from one API, and an API-key-only MCP connection suits your agent.
Choose Postiz instead of Hub when you must self-host or want open source, or when you publish to communities and blogs such as Reddit, Mastodon, Lemmy, WordPress or Medium.
Choose Buffer instead of Hub when your team already works in Buffer, you need a free plan for up to three channels, or several people need approval workflows and access levels.
Choose Blotato instead of Hub when AI images, video and voiceovers made in the same product matter more than server-side delegation controls, and a flat plan suits you.
Choose Mellow Hub when an AI agent publishes for you and you want its limits enforced by the server: channels per credential, review or autopilot, a daily ceiling, an expiry and a journal, with a required idempotency key, free validation and separate brand profiles.

Where Mellow Hub is weaker

No free publishing tier. Connecting accounts, drafting and validation are free, but publishing needs a plan, and the 7-day trial takes a card.
9 networks. No Reddit, Google Business Profile, Telegram, Discord, Slack, Mastodon, Snapchat or WhatsApp, and LinkedIn publishing goes to company pages rather than personal profiles.
A monthly allowance. Plans include 150, 600 or 1,500 publications a month, where most of the others advertise unlimited posts on paid plans, subject to fair use and each network’s own limits, and Outstand charges per post.
No comments, direct messages or inbox. Analytics are post-level: views and reach for recent posts, without account or follower analytics and without history from before your first reading.
One owner’s brands, not your customers’. There are no team seats, roles or client logins and no white-label connection flow, so Hub is not built for embedding social posting in your own product.
Newer than the rest. So far, Mellow’s own live tests have confirmed publication with public links on Instagram and Threads.

A worked example: three brands, 15 accounts

Three brands each run Instagram, TikTok, YouTube, Facebook and LinkedIn, so there are 15 connected accounts. Each brand publishes 12 posts a month to each of its five accounts: 36 posts, 180 deliveries. X is left out because several services bill it separately or need your own X developer app.

List prices checked 24 September 2026. Monthly billing, USD, before tax and add-ons.
Service	Plan that fits	Monthly	How it is counted
Ayrshare	Launch	$299	Three brands are three profiles; Premium includes one, Launch up to ten. Source: pricing
Blotato	Starter	$29	15 accounts within Starter’s 20. Source: rate card
Buffer	Essentials	$80	10 channels × $6 + 5 × $4. Team, which adds approval workflows, comes to $140. Source: pricing
Mellow Hub	Studio	$49	3 of 3 profiles; 180 of 600 publications. Source: pricing
Outstand	Pay as you go	$19	180 posts within the 3,000 included; accounts are free. Source: pricing
Postiz (hosted)	Pro	$49	15 channels need the 30-channel plan; Team has 10. Source: plans
Upload-Post	Basic	$24	Three profiles within Basic’s five; uploads unlimited. Sources: pricing, plan table
Zernio	Build, usage-based	$63	2 accounts free + 8 × $6 + 5 × $3. Source: pricing

On these list prices the workload costs from $19 (Outstand) to $299 (Ayrshare) a month; Mellow Hub’s Studio plan is $49. The prices buy different things: Ayrshare’s includes comments, direct messages and account analytics; Blotato’s includes AI credits for images and video; Hub’s includes delegation controls and 750 Studio AI credits a month; Outstand’s counts every delivery, including failed ones. Self-hosted Postiz has no licence fee but needs a server and your own developer apps for most networks. Recheck the linked prices before you buy.

Questions

Which social media posting APIs have an MCP server?

All eight compared here run a hosted MCP server: Ayrshare, Blotato, Buffer, Mellow Hub, Outstand, Postiz, Upload-Post and Zernio. They differ in how an agent signs in. Ayrshare accepts only an API key in a request header, and its docs say personal claude.ai and Claude Desktop connectors therefore cannot connect. The other seven also offer an OAuth sign-in; Mellow Hub, Upload-Post and Zernio document dynamic client registration with PKCE.

Which unified social media APIs have a free tier?

Checked 24 September 2026: Zernio’s first two connected accounts are free; Upload-Post’s free plan allows 10 uploads a month on two profiles, without TikTok; Buffer’s free plan covers three channels with 10 scheduled posts each and 3,000 API requests a month; self-hosted Postiz has no licence fee. Ayrshare offers a 28-day trial of its Launch plan without a card. Blotato and hosted Postiz offer 7-day trials, and Blotato’s trial excludes the API. Mellow Hub offers a 7-day trial with a card to eligible new subscribers; connecting accounts, drafting and validation are free, but publishing needs a plan. Outstand has no free tier.

What are the alternatives to Ayrshare, Zernio or Upload-Post?

They are alternatives to each other, and to Outstand (billed per post), Blotato (flat plans with AI content creation), Postiz (open source or hosted), Buffer (billed per channel, with a public GraphQL API) and Mellow Hub (brand profiles with server-side limits on what an agent may publish). Zernio was called Late until its rename; getlate.dev now redirects to zernio.com. Compare the billing unit first: for three brands with five accounts each and 12 posts per account a month, list prices checked on 24 September 2026 run from $19 (Outstand) to $299 (Ayrshare) a month.

How do I stop an AI agent from publishing the same post twice?

Send an idempotency key with every create request, so that a retry after a timeout returns the original post instead of publishing again. Mellow Hub requires one on every post. Outstand and Upload-Post accept an optional Idempotency-Key header, Zernio replays an x-request-id for about five minutes and rejects identical content to the same account for 24 hours, and Ayrshare rejects a repeated idempotencyKey. Buffer’s and Blotato’s docs say their create calls take no idempotency key, and Postiz’s docs do not mention one. Without a key, check whether the post exists before retrying.

Can I make an AI agent wait for human approval before it publishes?

In Mellow Hub, a key or OAuth grant in review mode can only prepare posts; a signed-in person approves them, and a key cannot approve its own post. Ayrshare can hold a post with requiresApproval until it is approved through its API, and Buffer offers approval workflows on its Team plan. Postiz collects comments on preview links but has no approval state that blocks publishing. The public docs of Zernio, Upload-Post, Outstand and Blotato do not describe a server-side approval step, although MCP clients may still ask you before each tool call.

Mellow Hub, Metricool, Buffer and Postiz: the same question for people who schedule by hand.
Schedule social media posts with a REST API: validate, schedule with an idempotency key and read each result.
Publish to social media with an MCP server: permissions, review mode and the delegation you give an agent.
API and MCP reference, generated from the rules Hub enforces.
Plans and the price calculator: each destination counts once against the monthly publications.