# ButterCMS vs Cosmic

> Cosmic scores 72.5 (BB) to ButterCMS's 51.4 (D) for content management. Prices, MCP, x402, uptime and agent notes side by side.

- Canonical: https://www.anchorterminal.com/compare/buttercms-vs-cosmic
- Markdown: https://www.anchorterminal.com/compare/buttercms-vs-cosmic.md (~4,500 tokens)
- Site index for agents: https://www.anchorterminal.com/llms.txt (the key docs and every listing in one file, at most 16 MB, about 4 million tokens: https://www.anchorterminal.com/llms-full.txt)
- API: https://www.anchorterminal.com/api/v1/index.json
- MCP: https://www.anchorterminal.com/mcp (the whole catalogue as tools, no key)
- DNS: dig +short TXT <slug>.grade.anchorterminal.com (the grade as a DNS TXT record, for a sandbox with no HTTP where names still resolve; also top., best.<category>. and <a>.vs.<b>. under the zone, and the same under grade.letme.dev)
- Licence: CC BY 4.0, credit Anchor Terminal and link this page (https://www.anchorterminal.com/terms/#data)
- Updated: 2026-11-07

Cosmic scores 72.5 (BB) on agent readiness against ButterCMS's 51.4 (D), and leads in every scored category. Both do content management.

- ButterCMS: grade D, 51.4/100, rank #1021 of 1486. Markdown https://www.anchorterminal.com/tools/buttercms.md · JSON https://www.anchorterminal.com/api/v1/tools/buttercms.json
- Cosmic: grade BB, 72.5/100, rank #123 of 1486. Markdown https://www.anchorterminal.com/tools/cosmic.md · JSON https://www.anchorterminal.com/api/v1/tools/cosmic.json
- Best headless CMS and website publishing for AI agents: https://www.anchorterminal.com/best/cms/index.md
- All 136 cms comparisons: https://www.anchorterminal.com/compare/cms/index.md

## Which one, for what

### ButterCMS (D)

Good for: A team already on a paid ButterCMS plan that wants an agent to draft and publish pages, collection items and blog posts in small volumes.

Watch for: The Write API is a paid add-on on Advanced ($249 a month) and Professional ($399), capped at 2,000 and 5,000 write calls a month. Its price is not published

### Cosmic (BB)

Good for: Teams that want an agent to set up and fill a hosted CMS end to end, including signup.

Ahead on:
- Reliability, 90 against 82
- Schema & documentation, 88 against 78
- Agent ergonomics, 82 against 64
- Security & auth, 47 against 31
- Payments & pricing, 45 against 20
- Maintenance & community, 86 against 17
- Transparency & trust, 63 against 52

Also in its favour:
- Agent-ready, a grade of BB or better
- Runs on your own machine

Watch for: No SOC 2, ISO 27001 or HIPAA certification, by the security page's own statement


## Why the edge

### Maintenance & community: Cosmic +69

- ButterCMS (17): No dated API changelog was found, and no dated API change in the docs. The docs sitemap's page dates record no change, so they don't set recency. The newest SDK release across the ten official SDKs is `buttercms` 3.0.3 on 4 September 2025 (Python 2.1.1 on 7 May 2024, .NET 2.1.1 on 16 April 2025, the others older), more than 180 days ago (0 of 30). No three releases or dated changelog entries in 90 days (0). Support by chat and email, a knowledge base and public SDK repositories, with no public changelog (5 of 15). Ten official SDKs are listed and none has a release in the last year (7 of 15, a partial kept). The JavaScript SDK has test and release workflows and moved to trusted publishing in November 2025, with no commits in the last 90 days (5 of 10).
- Cosmic (86): MCP server v1.7.1 was tagged on 2 November 2026 (30). v1.7.0 on 9 September and v1.7.1, plus changelog entries on 14 and 31 August, 1, 8, 10, 22 and 23 September and 5 and 9 October 2026 (20). A dated changelog, a Discord server and support email; GitHub issue activity wasn't read because the GitHub API refused us for its rate limit (12 of 25). com.cosmicjs/mcp in the official MCP registry under a domain namespace, though the registry has 1.6.0 while the repository is at 1.7.1 (15). CI, deploy and publish workflows in the MCP repository (9 of 10). 30+20+12+15+9 = 86.

### Payments & pricing: Cosmic +25

- ButterCMS (20): No x402, MPP or L402 (0). Four plans have public dollar prices, the Write API add-on's price is not published and Enterprise is through sales (10). The Free plan needs no card and covers the Read API. Writing needs a paid plan and the add-on, and we did not establish whether the 14-day trial includes it (10 of 20). A person signs up in a browser, and the write token needs a purchase or a request to support (0).
- Cosmic (45): No x402, MPP or L402 (0). Plan prices and quotas are public, with add-ons; no per-call price (10). Free plan with no card (20). Agent signup returns working bucket keys with no human signup; the human claims the project by emailed code within 14 days, so partial (15 of 20). 0+10+20+15 = 45.

### Agent ergonomics: Cosmic +18

- ButterCMS (64): Responses are sized with `page_size`, a `fields` selection, `exclude_body` on posts and `levels` for reference depth (20 of 25). Page and offset pagination with `meta.count`, filters on field values and `order` (20). Errors are documented with causes, but bodies come in three shapes (`detail`, a field map, `error`) with no stable codes, and a write answers 202 with `status: pending` and no identifier, so the result has to be read back (11 of 20). No idempotency keys. Page and post slugs are unique, which limits duplicates, and collection items have no such guard (4 of 20). Writes default to draft, but page creation needs every field key of the page type. Ten SDKs are listed and the docs say to call REST for writes (9 of 15).
- Cosmic (82): 24 tools, in the 11 to 30 band (15), plus 5 because omitting the write key gives a read-only subset (20 of 25). limit, props, depth, cursor pagination with `after`, status and locale filters (20). Status codes with specific messages and fix-or-retry guidance per code (17 of 20). readOnlyHint and destructiveHint on the MCP tools; no idempotency keys for writes, though agent signup is idempotent (14 of 20). Few required parameters, a TypeScript SDK and a CLI, no SDK in a second language found (11 of 15). 20+20+17+14+11 = 82.

### Security & auth: Cosmic +16

- ButterCMS (31): One read token and one write token per account, with no scopes, and the docs say rotation is done by contacting support (20 for plain revocable keys, less the fixed 10 because the read token is documented as an `auth_token` query parameter, 10 of 30). That token also returns drafts with `preview=1`. The read token is a read-only credential and writes default to draft. No approval step for API writes was found, and approval workflows are listed on Enterprise (10 of 20). The API returns stored content, and no guidance on treating it as untrusted input was found (3 of 15). Audit logs and access logs are listed as Enterprise functions, and versions record who saved them (6 of 15). A responsible-disclosure section in the docs gives security@buttercms.com and says reports get a prompt response, with no stated time, and the security page describes penetration tests. No security.txt, no bug bounty, and the certifications listed are those of the AWS and Heroku data centres (7 of 20).
- Cosmic (47): Separate read and write keys per bucket, rotatable independently (25), less 10 because the docs give `read_key` as a query parameter on GET (15 of 30). Read-only MCP access by leaving out the write key, four user roles on every plan, and a delete tool told not to run speculatively; no approval step (14 of 20). Objects hold text written by people and AI generation writes into the bucket; no prompt-injection guidance was found (3 of 15). An append-only audit log of security-relevant actions on Workspace or Pro plans (10 of 15). No SOC 2, ISO 27001 or HIPAA by the security page's own statement, no security.txt, reports to support email (5 of 20). 15+14+3+10+5 = 47.

### Transparency & trust: Cosmic +11

- ButterCMS (52): Closed service, MIT SDKs. The only published contract is an undated website Terms of Service that names no legal entity and has passages about collaborating on legal documents that do not describe a CMS (8 of 30). The privacy policy, last modified 15 August 2022, covers the website and says nothing about content stored in the CMS. The security page says data is kept as long as the customer needs it, the docs give 30 or more days for backups, and a DPA is on request for Enterprise customers (10 of 30). No deprecation policy or dated notice was found. PUT on pages is kept for backwards compatibility (2 of 20). Heroku, AWS, Fastly, Stripe and TinyMCE are named across the security page and docs. No sub-processor list or hosting region is published (6 of 20).
- Cosmic (63): A closed service; the MCP server is MIT (18 of 30). Terms and privacy policy of 13 January 2025 give general retention, and the security FAQ says data is kept indefinitely unless deletion is requested; storage in MongoDB Atlas is disclosed (15 of 30). Some fields are marked deprecated in v3 and the changelog is dated; no deprecation policy (8 of 20). The security page answers who the sub-processors are, but that answer wasn't readable in the page source (12 of 20). 18+15+8+12 = 53.

### Schema & documentation: Cosmic +10

- ButterCMS (78): Public OpenAPI 3.1 files for the whole API, the Read API, the Write API and webhooks, linked from the docs index. The combined file has 28 operations on 4 November 2026, 18 reads and 10 writes (25). A docs llms.txt and a Markdown copy of every docs page (10). All operations have a description, and the write descriptions state field rules, defaults and what the API cannot do. The docs say when to use an SDK and when to call REST (16 of 20). Request bodies have required fields and 40 enums in the combined file, but the `fields` object depends on each account's page types and no endpoint returns those types (9 of 15). 328 examples in the combined file and a page of status codes with causes and sample bodies (13 of 15). The version is in the `/v2` path. No API changelog was found (5 of 15).
- Cosmic (88): openapi.json at www.cosmicjs.com covers 21 operations on 12 paths, each with a summary, a description and documented 401, 402, 404, 429 and 500 responses, though the docs describe more endpoints than it covers (revisions, AI, search); MCP tools have typed inputs (20 of 25). llms.txt and every docs page as Markdown (10). Tool descriptions say when to use each tool and when not to, such as never calling delete speculatively (18 of 20). 11 enums in the spec, typed metafields and validation messages (11 of 15). Examples on every API page and an error model with a sample (14 of 15). API v3 paths and a dated changelog (15). 20+10+18+11+14+15 = 88.

## Score by category

| Category | Weight | ButterCMS | Cosmic | Edge |
| --- | --- | --- | --- | --- |
| Reliability | 16% (20 this run) | 82 | 90 | Cosmic +8 |
| Performance | 10%, pending | pending | pending | not scored in this run |
| Schema & documentation | 13% (16.2 this run) | 78 | 88 | Cosmic +10 |
| Agent ergonomics | 13% (16.2 this run) | 64 | 82 | Cosmic +18 |
| Security & auth | 14% (17.5 this run) | 31 | 47 | Cosmic +16 |
| Payments & pricing | 10% (12.5 this run) | 20 | 45 | Cosmic +25 |
| Task success | 10%, pending | pending | pending | not scored in this run |
| Maintenance & community | 7% (8.8 this run) | 17 | 86 | Cosmic +69 |
| Transparency & trust | 7% (8.8 this run) | 52 | 63 | Cosmic +11 |
| Negative events | ≤15 | -2 | 0 | |
| **Total** | | **51.4 · D** | **72.5 · BB** | |

## Facts side by side

| Fact | ButterCMS | Cosmic |
| --- | --- | --- |
| Kind | HTTP API | HTTP API |
| Vendor | ButterCMS LLC | Cosmic Inc. |
| Hosted endpoint | `https://api.buttercms.com/v2` | `https://mcp.cosmicjs.com/v1/buckets/{bucket_slug}` |
| Transports | HTTP | HTTP, Streamable HTTP, stdio |
| Auth | API key | API key |
| Pricing | Freemium | Freemium |
| x402 | no | no |
| Licence | Proprietary service under ButterCMS's terms of service. The SDKs and starter projects on GitHub are MIT | none |
| Tools exposed | none | 24 |
| Read-only variant documented | no | yes |
| llms.txt | yes | yes |
| MCP registry | not listed | `com.cosmicjs/mcp` |
| Last release | 2025-09-04 | 2026-11-02 |
| Terms last updated | no date given | no date given |
| Privacy policy last updated | 2022-08-15 | no date given |
| Customer content may train models | not found in the text | not found in the text |
| Terms restrict automated access | not found in the text | yes |
| Terms restrict benchmarking | not found in the text | not found in the text |
| Terms or service can change without notice | not found in the text | not found in the text |
| Arbitration or class-action waiver | not found in the text | yes |
| Popularity | 6.9k npm/wk | 295 npm/wk |

## How the scores have moved

### ButterCMS

- -2.0 on 4 November 2026: checklist
- +0.1 on 28 October 2026: new evidence

### Cosmic

No score change since it was listed.

## Verdicts

**ButterCMS.** The Read and Write APIs have a public OpenAPI 3.1 file, Markdown docs and a status page with no incident since October 2025. The Write API is a paid add-on from the $249 plan, capped at 2,000 or 5,000 calls a month. Writes answer 202 with no identifier, and no SDK has had a release since September 2025.

**Cosmic.** Cosmic gives agents 24 annotated MCP tools with when-to-use descriptions, a read-only mode by key, documented limits and an agent signup API that returns working keys before a human claims the project. It holds no SOC 2 or ISO certification by its own statement, and read keys can travel in the URL.

## Before you call either

### ButterCMS

1. End every path with a slash. A missing slash returns a 301, and the vendor counts the redirect and the retry as two API calls
2. Send the write token only as `Authorization: Token <token>`. The `auth_token` query parameter works for reads only
3. On page creation send every field key of the page type, with empty strings for fields left blank
4. A 202 means queued, not saved. Read the entry back with `preview=1` to confirm, and check a slug exists before retrying a create
5. Call the REST API directly for writes. The JavaScript SDK 3.0.3 has list, retrieve and search methods only

### Cosmic

1. Send only the read key in the Bearer token unless the task needs writes
2. Use cosmic_agent_signup when the user has no Cosmic account, and hand the human the claim URL within 14 days
3. Fix and don't retry on 400; wait and retry on 429
4. Use props, depth=0 and cursor pagination with `after` to stay under the 6 MB response limit
5. Confirm with the user before cosmic_objects_delete, which deletes permanently

## Questions

### Which is better for AI agents, ButterCMS or Cosmic?

Cosmic scores 72.5 (BB) on agent readiness against ButterCMS's 51.4 (D), and leads in every scored category.

### Do ButterCMS and Cosmic need an API key?

Both need an API key.

### Can an agent call ButterCMS and Cosmic without installing anything?

Yes. ButterCMS has a hosted endpoint at https://api.buttercms.com/v2 and Cosmic at https://mcp.cosmicjs.com/v1/buckets/{bucket_slug}.


## For agents

- This comparison as JSON: https://www.anchorterminal.com/compare/buttercms-vs-cosmic.json, and with the fewest tokens: https://www.anchorterminal.com/compare/buttercms-vs-cosmic.min.md
- Over MCP at https://www.anchorterminal.com/mcp (no key): `compare_tools {"a": "buttercms", "b": "cosmic"}`. From a terminal: `anchor compare buttercms cosmic`
- Each listing in full: https://www.anchorterminal.com/api/v1/tools/buttercms.json and https://www.anchorterminal.com/api/v1/tools/cosmic.json

## Other comparisons with ButterCMS or Cosmic

- [BCMS vs ButterCMS](https://www.anchorterminal.com/compare/bcms-vs-buttercms.md)
- [BCMS vs Cosmic](https://www.anchorterminal.com/compare/bcms-vs-cosmic.md)
- [ButterCMS vs Contentstack](https://www.anchorterminal.com/compare/buttercms-vs-contentstack.md)
- [ButterCMS vs DatoCMS](https://www.anchorterminal.com/compare/buttercms-vs-datocms.md)
- [ButterCMS vs Directus](https://www.anchorterminal.com/compare/buttercms-vs-directus.md)
- [ButterCMS vs dotCMS](https://www.anchorterminal.com/compare/buttercms-vs-dotcms.md)
- [ButterCMS vs Ghost](https://www.anchorterminal.com/compare/buttercms-vs-ghost.md)
- [ButterCMS vs Hygraph](https://www.anchorterminal.com/compare/buttercms-vs-hygraph.md)
- [ButterCMS vs Kontent.ai](https://www.anchorterminal.com/compare/buttercms-vs-kontent-ai.md)
- [ButterCMS vs Payload](https://www.anchorterminal.com/compare/buttercms-vs-payload.md)
- [ButterCMS vs Prismic](https://www.anchorterminal.com/compare/buttercms-vs-prismic.md)
- [ButterCMS vs Sanity](https://www.anchorterminal.com/compare/buttercms-vs-sanity.md)
- [ButterCMS vs Storyblok](https://www.anchorterminal.com/compare/buttercms-vs-storyblok.md)
- [ButterCMS vs Strapi](https://www.anchorterminal.com/compare/buttercms-vs-strapi.md)
- [ButterCMS vs Webflow](https://www.anchorterminal.com/compare/buttercms-vs-webflow.md)
- [ButterCMS vs WordPress](https://www.anchorterminal.com/compare/buttercms-vs-wordpress.md)
- [Contentstack vs Cosmic](https://www.anchorterminal.com/compare/contentstack-vs-cosmic.md)
- [Cosmic vs DatoCMS](https://www.anchorterminal.com/compare/cosmic-vs-datocms.md)
- [Cosmic vs Directus](https://www.anchorterminal.com/compare/cosmic-vs-directus.md)
- [Cosmic vs dotCMS](https://www.anchorterminal.com/compare/cosmic-vs-dotcms.md)
- [Cosmic vs Ghost](https://www.anchorterminal.com/compare/cosmic-vs-ghost.md)
- [Cosmic vs Hygraph](https://www.anchorterminal.com/compare/cosmic-vs-hygraph.md)
- [Cosmic vs Kontent.ai](https://www.anchorterminal.com/compare/cosmic-vs-kontent-ai.md)
- [Cosmic vs Payload](https://www.anchorterminal.com/compare/cosmic-vs-payload.md)
- [Cosmic vs Prismic](https://www.anchorterminal.com/compare/cosmic-vs-prismic.md)
- [Cosmic vs Sanity](https://www.anchorterminal.com/compare/cosmic-vs-sanity.md)
- [Cosmic vs Storyblok](https://www.anchorterminal.com/compare/cosmic-vs-storyblok.md)
- [Cosmic vs Strapi](https://www.anchorterminal.com/compare/cosmic-vs-strapi.md)
- [Cosmic vs Webflow](https://www.anchorterminal.com/compare/cosmic-vs-webflow.md)
- [Cosmic vs WordPress](https://www.anchorterminal.com/compare/cosmic-vs-wordpress.md)

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Query this catalogue directly over MCP: https://www.anchorterminal.com/mcp (Streamable HTTP, no key). How: https://www.anchorterminal.com/agents/#mcp