oeis-mcp-server

Get OEIS Cross-References

oeis_get_cross_refs

Read-onlyIdempotent

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 Schema

TableJSON Schema

Name	Required	Description	Default
`start`	No	Row offset: 0, 10, … 100 (at most 110 rows are reachable per entry and direction). Pass nextStart from the previous page.
`aNumber`	Yes	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. Legacy M/N book numbers (e.g. "M1459") are not A-numbers: find them with oeis_search_sequences.
`direction`	No	outgoing (default): the A-numbers this entry cross-references. incoming: the entries that mention this A-number.	outgoing

Output Schema

TableJSON Schema

Name	Required	Description
`cap`	No	Page size: 10, fixed by OEIS.
`error`	No	Present when the call failed. Absent on success.
`lines`	No	Outgoing only: the entry's cross-reference lines verbatim, written by OEIS contributors; lineIndex points into this list.
`shown`	No	Rows on this page.
`start`	No	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).
`notice`	No	Guidance: why nothing matched, how to narrow the query, or how to reach the next page.
`aNumber`	No	The entry whose relations are listed, e.g. "A000045".
`related`	No	Related sequences on this page: outgoing in order of first mention, incoming in OEIS relevance order.
`direction`	No	The direction listed.
`nextStart`	No	Pass as start for the next page; absent on the last reachable page.
`truncated`	No	True when more rows exist than this page shows.
`totalCount`	No	Total rows: the match count OEIS reported, or for outgoing cross-references the number of distinct A-numbers the entry names.
`effectiveQuery`	No	The query as OEIS parsed it (lowercased upstream), e.g. seq:1,2,5,14,42.

Schema Changelog

Changes observed during successful MCP inspections.

First observedOct 2, 2026

TDQS

A4/5.0

Behavior4/5

Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?

Annotations already declare readOnly/idempotent/openWorld, so the bar is lower, yet the description still adds real behavior: page size ('10 rows per page'), what each row contains, and what the outgoing mode includes (parenthetical notes). It does not mention rate limits or auth, but for a read-only lookup tool that is a minor omission.

Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.

Conciseness5/5

Is the description appropriately sized, front-loaded, and free of redundancy?

Four short sentences, zero filler, and the core capability is front-loaded before the mode semantics. The pagination fact is included economically rather than as its own paragraph.

Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.

Completeness4/5

Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?

With an output schema present the description need not explain return values, and it nonetheless sketches the row shape. Combined with the direction semantics and page-size note, an agent has enough to call this correctly; only sibling disambiguation is absent.

Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.

Parameters3/5

Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?

Schema coverage is 100% and the schema itself already documents start, aNumber normalization, and the direction enum, so baseline is 3. The description adds only marginal detail beyond that, mainly the parenthetical-note behavior for outgoing, which the schema does not state.

Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.

Purpose4/5

Does the description clearly state what the tool does and how it differs from similar tools?

States a specific verb and resource ('List sequences related to an OEIS entry') and splits the behavior into two clearly defined modes, so an agent can tell it apart from oeis_get_sequence or oeis_get_terms. It never names a sibling tool to sharpen the boundary, which keeps it short of a 5.

Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.

Usage Guidelines4/5

Does the description explain when to use this tool, when not to, or what alternatives exist?

The direction semantics ('outgoing returns the A-numbers named in the Cf. lines' vs 'incoming returns entries that mention this A-number anywhere') give clear context for choosing the right mode. It offers no guidance about when to prefer this tool over sibling tools such as oeis_list_reference or oeis_search_sequences, and states no exclusions.

Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.

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