# io.github.cyanheads/oeis-mcp-server (remote · oeis.caseyjhand.com)

Identify integer sequences by terms, search the OEIS, read formulas, programs, b-files, cross-refs.

- Trust score: 87/100 (high trust)
- Change this week: +1
- Registry status: active
- Liveness: live
- Owner verified: no
- Last scored: 2026-11-05

## Components

- remote · `oeis.caseyjhand.com`: 87/100 (this document), [markdown](https://verifymcp.io/servers/cyanheads-oeis-mcp-server/oeis.md), [page](https://verifymcp.io/servers/cyanheads-oeis-mcp-server/oeis)
- npm · `@cyanheads/oeis-mcp-server`: 82/100, [markdown](https://verifymcp.io/servers/cyanheads-oeis-mcp-server/cyanheads-oeis-mcp-server.md), [page](https://verifymcp.io/servers/cyanheads-oeis-mcp-server/cyanheads-oeis-mcp-server)

## Channel facts

- Endpoint: `https://oeis.caseyjhand.com/mcp`
- Transports: `streamable-http`
- Auth: `none`
- Version: `0.1.3`

## Trust breakdown

How this component scores in each security and reliability category. Every signal is checked automatically against the live server, and we only credit what we can confirm. Scores are 0–100 per category. Scoring method: https://verifymcp.io/docs/scoring (what has changed: https://verifymcp.io/docs/scoring/changelog)

Scored 2026-11-05.

- **Endpoint Security**: 83/100
  - The endpoint's TLS certificate is valid, in date, and uses a strong key.
  - No authorisation is required to call this server. Nothing on it is marked destructive, but we can't show that an anonymous caller can only read: full credit needs the server to list at least one tool and every tool to be verifiably read-only. We use a best-effort check of tool names and descriptions to tell read-only tools from tools that change things, so some genuinely read-only tools may not get full credit. Names that start with a read verb (get, list, read, search and similar) and accurate readOnlyHint annotations help. Meet that to earn full credit, or require authorisation.
  - HTTPS is enforced; there's no plaintext access path.
  - The HSTS (Strict-Transport-Security) header is present.
  - DNSSEC is configured correctly; the domain's records validate against the full chain to the root.
- **Transport & Reachability**: 100/100
  - Verified streamable-http transport via a live MCP handshake.
- **Schema Quality & AI Usability**: 66/100
  - AI-judged instruction clarity (excellent).
  - Context-footprint check failed: tool/resource definitions use about 1801 tokens (~300/item across 6 items; 6 tools + 0 resources), over budget; trim descriptions and params.
  - Usage-examples check failed: none of the tools include examples.
- **Stability & Change Management**: 100/100
  - No destabilizing schema changes in the last 30 days.
- **Tool Coverage**: 100/100
  - 100% of tools have a non-trivial description (not blank, and not just the tool's name).
  - 100% of tool parameters carry a description.
  - Structured output schemas are declared (100% of tools); any adoption earns full credit.
- **Tool Safety**: 100/100
  - No prompt-injection markers were found in the server instructions, tool names or descriptions we captured.
  - We read all 6 captured tool definition(s), and no name or description among them implies an irreversible operation.
  - An AI judge read all 7 captured unit(s) of tool text and found none that tries to manipulate the model reading it.
- **Capabilities**: 100/100
  - Implements a current MCP spec version (2026-07-28).

## Install

### How do I install the io.github.cyanheads/oeis-mcp-server server?

io.github.cyanheads/oeis-mcp-server is a hosted endpoint at https://oeis.caseyjhand.com/mcp, so there is nothing to install locally. Ready-made configuration for Claude, Cursor, VS Code, Codex and 5 more is on this page, copied from each client's own documentation.

### Claude

```bash
claude mcp add --transport http cyanheads-oeis-mcp-server 'https://oeis.caseyjhand.com/mcp'
```

### Cursor

```json
{
  "mcpServers": {
    "cyanheads-oeis-mcp-server": {
      "url": "https://oeis.caseyjhand.com/mcp"
    }
  }
}
```

### VS Code

```json
{
  "servers": {
    "cyanheads-oeis-mcp-server": {
      "type": "http",
      "url": "https://oeis.caseyjhand.com/mcp"
    }
  }
}
```

### Codex

```toml
[mcp_servers.cyanheads-oeis-mcp-server]
url = "https://oeis.caseyjhand.com/mcp"
```

### opencode

```json
{
  "$schema": "https://opencode.ai/config.json",
  "mcp": {
    "cyanheads-oeis-mcp-server": {
      "type": "remote",
      "url": "https://oeis.caseyjhand.com/mcp",
      "enabled": true
    }
  }
}
```

### OpenClaw

```bash
openclaw mcp add cyanheads-oeis-mcp-server --url 'https://oeis.caseyjhand.com/mcp' --transport streamable-http
```

### Hermes

```yaml
mcp_servers:
  cyanheads-oeis-mcp-server:
    url: "https://oeis.caseyjhand.com/mcp"
```

### Netclaw

```json
{
  "McpServers": {
    "cyanheads-oeis-mcp-server": {
      "Transport": "http",
      "Url": "https://oeis.caseyjhand.com/mcp"
    }
  }
}
```

### Vellum

```bash
assistant mcp add cyanheads-oeis-mcp-server -t streamable-http -u 'https://oeis.caseyjhand.com/mcp'
```

### Other

```json
{
  "mcpServers": {
    "cyanheads-oeis-mcp-server": {
      "type": "http",
      "url": "https://oeis.caseyjhand.com/mcp"
    }
  }
}
```

The mcpServers block is a cross-client convention. Remote transports vary, so check your client's docs.

## Changelog

Every change recorded for this component, newest first. Days that predate change tracking, or that we cannot explain, say so: "we were watching and nothing happened" and "we were not watching" are different claims.

### 2026-11-01 (score 87, 0)

- [security] Stability: 0.97 → pass

### 2026-10-31 (score 87, +1)

No change was recorded against any check on this day. Stability & Change Management went from 93 to 97. That category is still filling its 30-day observation window: 28 days of observed history at the previous scan, 29 at this one. The score rises as the window fills, whether or not the server changes.

### 2026-10-29 (score 86, +1)

No change was recorded against any check on this day. Stability & Change Management went from 87 to 90. That category is still filling its 30-day observation window: 26 days of observed history at the previous scan, 27 at this one. The score rises as the window fills, whether or not the server changes.

### 2026-10-27 (score 85, +1)

No change was recorded against any check on this day. Stability & Change Management went from 80 to 83. That category is still filling its 30-day observation window: 24 days of observed history at the previous scan, 25 at this one. The score rises as the window fills, whether or not the server changes.

### 2026-10-25 (score 84, +1)

No change was recorded against any check on this day. Stability & Change Management went from 73 to 77. That category is still filling its 30-day observation window: 22 days of observed history at the previous scan, 23 at this one. The score rises as the window fills, whether or not the server changes.

### 2026-10-23 (score 83, +1)

No change was recorded against any check on this day. Stability & Change Management went from 67 to 70. That category is still filling its 30-day observation window: 20 days of observed history at the previous scan, 21 at this one. The score rises as the window fills, whether or not the server changes.

### 2026-10-21 (score 82, +1)

No change was recorded against any check on this day. Stability & Change Management went from 60 to 63. That category is still filling its 30-day observation window: 18 days of observed history at the previous scan, 19 at this one. The score rises as the window fills, whether or not the server changes.

### 2026-10-18 (score 81, +1)

- [security] Tool “oeis_get_terms” rewrote its description, which is the text the model reads
- [functional] Server version: 0.1.2 → 0.1.3
- [cosmetic] “oeis_search_sequences” reworded the description of “query”
- [cosmetic] “oeis_get_terms” reworded the description of “limit”

## MCP tools (6)

### `oeis_identify_sequence` (~298 tokens)

Identify OEIS Sequence

Identify integer sequences that contain a run of consecutive terms, e.g. "1, 2, 5, 14, 42". Returns up to 10 matches per page in OEIS relevance order, each with the index n at which the supplied run begins. For the best hit rate supply about 6 terms and leave off the first one or two, since sources disagree on where a sequence starts. OEIS matches only the first terms of each entry (its data line, at most about 270 characters), not its b-file, so a run from far into a sequence is not found. Takes up to 60 terms, each an integer of at most 200 digits or the wildcard _ for one unknown term.

Input parameters:

- `matchSigns` (boolean): false (default) matches ignoring signs, so a sign-convention difference does not hide the sequence; true requires the signs to match.
- `start` (integer): Result offset: 0, 10, … 100 (OEIS shows at most 110 results per query). Pass nextStart from the previous page.
- `terms` (string, required): Up to 60 consecutive terms separated by commas or spaces, e.g. "1, 2, 5, 14, 42" (a bracketed list or a trailing ... is accepted). Each term is an integer of at most 200 digits, or _ for a single unk…

Output parameters:

- `cap` (number): Page size: 10, fixed by OEIS.
- `effectiveQuery` (string): The query as OEIS parsed it (lowercased upstream), e.g. seq:1,2,5,14,42.
- `error` (object): Present when the call failed. Absent on success.
- `nextStart` (number): Pass as start for the next page; absent on the last reachable page.
- `notice` (string): Guidance: why nothing matched, how to narrow the query, or how to reach the next page.
- `results` (array): Candidate sequences on this page, in OEIS relevance order.
- `shown` (number): Rows on this page.
- `start` (number): The result offset of this page as OEIS served it; below the requested start when that start was past the last result (OEIS then serves the last page).
- `totalCount` (number): Total rows: the match count OEIS reported, or for outgoing cross-references the number of distinct A-numbers the entry names.
- `truncated` (boolean): True when more rows exist than this page shows.

### `oeis_search_sequences` (~250 tokens)

Search OEIS Sequences

Search the OEIS using its query syntax: plain words, "quoted phrases", comma-separated terms, prefixes (keyword:, author:, name:, comment:, formula:, program:, xref:, id:), | for OR, and a leading - to exclude. Returns up to 10 summaries per page. For identifying a sequence from its terms, oeis_identify_sequence is the direct route.

Input parameters:

- `query` (string, required): OEIS query, sent as written. Examples: keyword:core fibonacci; author:Sloane; "Catalan numbers" (a quoted phrase); 1,2,5,14,42 (separate terms with commas: with spaces alone, a negative term after th…
- `sort` (string): Result order: relevance (default), number (ascending A-number), created (newest entry first), or modified (most recently edited first).
- `start` (integer): Result offset: 0, 10, … 100 (OEIS shows at most 110 results per query). Pass nextStart from the previous page.

Output parameters:

- `cap` (number): Page size: 10, fixed by OEIS.
- `effectiveQuery` (string): The query as OEIS parsed it (lowercased upstream), e.g. seq:1,2,5,14,42.
- `error` (object): Present when the call failed. Absent on success.
- `nextStart` (number): Pass as start for the next page; absent on the last reachable page.
- `notice` (string): Guidance: why nothing matched; that OEIS split the numbers into separate searches, and how to join them with commas into one run; how to narrow the query; or how to reach the next page.
- `results` (array): Matching sequences on this page, in the applied order.
- `shown` (number): Rows on this page.
- `sort` (string): The result order applied.
- `start` (number): The result offset of this page as OEIS served it; below the requested start when that start was past the last result (OEIS then serves the last page).
- `totalCount` (number): Total rows: the match count OEIS reported, or for outgoing cross-references the number of distinct A-numbers the entry names.
- `truncated` (boolean): True when more rows exist than this page shows.

### `oeis_get_sequence` (~356 tokens)

Get OEIS Sequence

Fetch one OEIS entry by A-number. Returns the name, data-line terms, offset, keywords, author, dates, and the sections: comments, formulas (recurrences and generating functions), examples, programs (Maple, Mathematica, PARI, Python, …), references, links, cross-references, and extensions. When the sections together exceed 24,000 characters of serialized JSON, the core fields come back with a section outline instead; call again with sections to pick what to read. A selection past 100,000 bytes comes back in parts cut between items: pass nextFromItem as fromItem, with the same sections, for the next part.

Input parameters:

- `aNumber` (string, required): OEIS A-number, e.g. "A000045"; oeis_identify_sequence and oeis_search_sequences return them. Also accepts "a000045", "A45", "45", and an oeis.org sequence URL; all normalize to the zero-padded form.…
- `fromItem` (object): Where to resume a cut selection: the previous response's nextFromItem, passed unchanged with the same sections. The selected sections before fromItem.section are left out. Omit to start at the beginn…
- `sections` (array): Sections to return with the core fields, e.g. ["formulas", "programs"]. A selection past the 100,000-byte response budget is cut between items; fromItem continues it. Omit (or pass []) for the full e…

Output parameters:

- `aNumber` (string): A-number, e.g. "A000045".
- `author` (string): Author line as OEIS records it; absent when the entry has none.
- `bFileUrl` (string): URL of the entry's b-file of extended terms; oeis_get_terms reads it.
- `comments` (array): Comment lines, one element per upstream line, written by OEIS contributors. Present on a full entry or when selected; a cut selection carries only this part's lines.
- `created` (string): When the entry was created, ISO 8601 with offset.
- `crossReferences` (array): Cross-reference lines naming related A-numbers, one element per upstream line, written by OEIS contributors. Present on a full entry or when selected; a cut selection carries only this part's lines.
- `error` (object): Present when the call failed. Absent on success.
- `examples` (array): Example lines; whitespace matters for triangles and tables, one element per upstream line, written by OEIS contributors. Present on a full entry or when selected; a cut selection carries only this pa…
- `extensions` (array): Extension lines: who added terms or corrections, and when, one element per upstream line, written by OEIS contributors. Present on a full entry or when selected; a cut selection carries only this par…
- `firstIndex` (number): The index n of the first term (the first number of offset); absent with offset.
- `formulas` (array): Formula lines: recurrences, generating functions, closed forms, one element per upstream line, written by OEIS contributors. Present on a full entry or when selected; a cut selection carries only thi…
- `keywords` (array): Keyword flags such as nonn, core, tabl; oeis_list_reference topic keywords decodes them.
- `kind` (string): full: every section, or the selected ones (a selection past the 100,000-byte response budget is cut between items, and nextFromItem continues it). outline: the entry is too large, so sections lists t…
- `legacyIds` (array): Legacy book numbers, e.g. ["M0692", "N0256"]; absent on entries that have none.
- `links` (array): Link lines. Present on a full entry or when selected; a cut selection carries only this part's lines.
- `modified` (string): When the entry was last edited, ISO 8601 with offset.
- `name` (string): Sequence name, written by OEIS contributors.
- `nextFromItem` (object): Present when the selection was cut at the 100,000-byte response budget: the first item left out. Pass it unchanged as fromItem, with the same sections, to continue.
- `notice` (string): Guidance: the entry is withdrawn (dead) or its A-number reserved or recycled; where a cut selection stopped and the call that continues it; or that fromItem lies past the end of its section.
- `offset` (string): Offset "i,p": i is the index n of the first term, p the 1-based position of the first term with |a(n)| > 1. Absent on a reserved or recycled A-number (keyword allocated or recycled).
- `outlineNotice` (string): Outline only: how to request sections, and how a large selection continues.
- `programs` (array): Programs that compute the terms. Present on a full entry or when selected; a cut selection carries only this part's blocks.
- `referenceCount` (number): How many OEIS entries mention this A-number, the entry itself included.
- `references` (array): Reference lines (books and papers), one element per upstream line, written by OEIS contributors. Present on a full entry or when selected; a cut selection carries only this part's lines.
- `revision` (number): Revision number of the entry.
- `sections` (array): Outline only: the sections of the entry, largest first.
- `terms` (array): Data-line terms as exact decimal strings, signs kept; the first is a(firstIndex).
- `url` (string): Sequence page on oeis.org; cite it wherever the entry is reused.

### `oeis_get_terms` (~306 tokens)

Get OEIS Sequence Terms

List terms a(n) of a sequence with their indices n. Reads the entry's b-file when it has one — often thousands of terms beyond the data line — and otherwise the data line itself. Values are exact decimal strings of any size. A slice stops at limit terms (at most 1000 per call), at about 100,000 bytes, or at the end of one 1 MiB part of a larger b-file, whichever comes first; nextFromIndex continues it.

Input parameters:

- `aNumber` (string, required): OEIS A-number, e.g. "A000045"; oeis_identify_sequence and oeis_search_sequences return them. Also accepts "a000045", "A45", "45", and an oeis.org sequence URL; all normalize to the zero-padded form.…
- `fromIndex` (integer): First index n to return; defaults to the first available index. Pass nextFromIndex from the previous call to continue.
- `limit` (integer): Maximum number of terms to return (default 100). One call returns at most 1000, so a larger limit is served as 1000. A slice stops sooner at about 100,000 bytes of large terms or at the end of one 1…

Output parameters:

- `aNumber` (string): A-number, e.g. "A000045".
- `bFileCut` (boolean): True while the b-file goes on past lastAvailableIndex. Its later terms are at bFileUrl; nextFromIndex or a larger fromIndex reaches them unless the notice says only the first 1 MiB was read.
- `bFileSizeInBytes` (number): Full size of the b-file as OEIS reported it; absent when not reported.
- `bFileUrl` (string): URL of the b-file the terms came from; absent when source is data.
- `cap` (number): The limit that was applied: limit, or 1000 when limit is larger.
- `error` (object): Present when the call failed. Absent on success.
- `firstAvailableIndex` (number): Lowest index n read for this entry; absent when no terms were read.
- `lastAvailableIndex` (number): Highest index n read so far for this entry; when bFileCut is true the b-file goes on past it. Absent when no terms were read.
- `nextFromIndex` (number): Pass as fromIndex for the next slice. Absent when no slice follows this one: the terms ended, or the notice says how to reach the rest.
- `notice` (string): Guidance: where the next slice starts and whether the byte budget ended this one, why no terms came back (past the last index, or not yet reached in a large b-file), that a b-file line too long to re…
- `shown` (number): Terms in this slice.
- `source` (string): bfile: read from the entry's b-file of extended terms. data: the entry has no b-file, so these are its data-line terms.
- `terms` (array): Terms in index order, from the first index at or after fromIndex (or the first available index).
- `truncated` (boolean): True when nextFromIndex is set.
- `url` (string): Sequence page on oeis.org; cite it wherever the terms are reused.

### `oeis_get_cross_refs` (~237 tokens)

Get OEIS Cross-References

List sequences related to an OEIS entry. direction outgoing returns the A-numbers named in the entry's cross-reference (Cf.) lines, with any parenthetical note beside each; direction incoming returns entries that mention this A-number anywhere. Each row carries the related sequence's name and first terms. 10 rows per page.

Input parameters:

- `aNumber` (string, required): OEIS A-number, e.g. "A000045"; oeis_identify_sequence and oeis_search_sequences return them. Also accepts "a000045", "A45", "45", and an oeis.org sequence URL; all normalize to the zero-padded form.…
- `direction` (string): outgoing (default): the A-numbers this entry cross-references. incoming: the entries that mention this A-number.
- `start` (integer): Row offset: 0, 10, … 100 (at most 110 rows are reachable per entry and direction). Pass nextStart from the previous page.

Output parameters:

- `aNumber` (string): The entry whose relations are listed, e.g. "A000045".
- `cap` (number): Page size: 10, fixed by OEIS.
- `direction` (string): The direction listed.
- `effectiveQuery` (string): The query as OEIS parsed it (lowercased upstream), e.g. seq:1,2,5,14,42.
- `error` (object): Present when the call failed. Absent on success.
- `lines` (array): Outgoing only: the entry's cross-reference lines verbatim, written by OEIS contributors; lineIndex points into this list.
- `nextStart` (number): Pass as start for the next page; absent on the last reachable page.
- `notice` (string): Guidance: why nothing matched, how to narrow the query, or how to reach the next page.
- `related` (array): Related sequences on this page: outgoing in order of first mention, incoming in OEIS relevance order.
- `shown` (number): Rows on this page.
- `start` (number): The row offset of this page. For incoming, as OEIS served it: below the requested start when that start was past the last entry (OEIS then serves the last page).
- `totalCount` (number): Total rows: the match count OEIS reported, or for outgoing cross-references the number of distinct A-numbers the entry names.
- `truncated` (boolean): True when more rows exist than this page shows.

### `oeis_list_reference` (~123 tokens)

List OEIS Reference

Look up OEIS vocabulary used by the other tools: keyword flags (nonn, core, tabl, cons, …), search syntax (prefixes, operators, wildcards, sort orders, paging window), and identifier conventions (A-numbers, legacy M/N numbers, offsets, b-files).

Input parameters:

- `topic` (string, required): keywords: keyword flags such as nonn, core, tabl. search_syntax: prefixes, operators, wildcards, sort orders, and paging. identifiers: A-numbers, legacy M/N numbers, offsets, and b-files.

Output parameters:

- `entries` (array): Vocabulary entries for the topic.
- `error` (object): Present when the call failed. Absent on success.
- `notes` (array): Usage notes that apply across the topic.
- `topic` (string): The topic listed.

## Diagnostics

Captured diagnostic sections: TLS, DNSSEC, Authorisation, Transports. The full working is on the page: https://verifymcp.io/servers/cyanheads-oeis-mcp-server/oeis#diagnostics

## Score history

- 2026-11-05: 87
- 2026-11-04: 87
- 2026-11-03: 87
- 2026-11-02: 87
- 2026-11-01: 87
- 2026-10-31: 87
- 2026-10-30: 86
- 2026-10-29: 86
- 2026-10-28: 85
- 2026-10-27: 85
- 2026-10-26: 84
- 2026-10-25: 84
- 2026-10-24: 83
- 2026-10-23: 83
- 2026-10-22: 82
- 2026-10-21: 82
- 2026-10-20: 81
- 2026-10-19: 81
- 2026-10-18: 81
- 2026-10-17: 80
- 2026-10-16: 80
- 2026-10-15: 79
- 2026-10-14: 79
- 2026-10-13: 78
- 2026-10-12: 78
- 2026-10-10: 77
- 2026-10-07: 75
- 2026-10-04: 74
- 2026-10-03: 74
- 2026-10-02: 73

## Common questions

### What is the io.github.cyanheads/oeis-mcp-server server?

io.github.cyanheads/oeis-mcp-server is listed in the public MCP registry as io.github.cyanheads/oeis-mcp-server. Identify integer sequences by terms, search the OEIS, read formulas, programs, b-files, cross-refs. This page covers its hosted endpoint (https://oeis.caseyjhand.com/mcp).

### Is the io.github.cyanheads/oeis-mcp-server server safe to use?

io.github.cyanheads/oeis-mcp-server scores 87 out of 100 on VerifyMCP. That is a record of what we were able to check automatically, not an endorsement. The category breakdown on this page shows every signal behind the number, including the ones we could not confirm.

### What tools does the io.github.cyanheads/oeis-mcp-server server expose?

io.github.cyanheads/oeis-mcp-server exposes 6 tools: oeis_identify_sequence, oeis_search_sequences, oeis_get_sequence, oeis_get_terms, oeis_get_cross_refs, oeis_list_reference. Their descriptions and schemas cost roughly 1,570 tokens of context every time the server is loaded.

### Does the io.github.cyanheads/oeis-mcp-server server require authentication?

No. We connected to io.github.cyanheads/oeis-mcp-server without credentials and it answered, so anything it exposes is reachable by anyone who knows the address.

### Is the io.github.cyanheads/oeis-mcp-server server still maintained?

io.github.cyanheads/oeis-mcp-server is still listed as active in the MCP registry. We last reached this channel on 5 November 2026. Those dates come from our own scans of the registry and the channel itself, not from anything the publisher announced.

### What did VerifyMCP test on the io.github.cyanheads/oeis-mcp-server server?

VerifyMCP ran 13 checks on io.github.cyanheads/oeis-mcp-server, covering TLS certificate, Authorization, HTTPS, HSTS header and 9 more. Supply Chain Security and Provenance & Transparency do not apply to a hosted endpoint, so they were not tested. The score does not measure everything, and the scoring documentation lists what it leaves out.

## Links

- Remote endpoint: https://oeis.caseyjhand.com/mcp
- Repository: https://github.com/cyanheads/oeis-mcp-server
- Changelog RSS feed: https://verifymcp.io/servers/cyanheads-oeis-mcp-server/oeis.xml
- Changelog JSON feed: https://verifymcp.io/servers/cyanheads-oeis-mcp-server/oeis/changelog.json
- Trust report (JSON): https://verifymcp.io/servers/cyanheads-oeis-mcp-server/oeis.json
- HTML version of this page: https://verifymcp.io/servers/cyanheads-oeis-mcp-server/oeis