# Scholar Sidekick

> Citation resolver, formatter, and exporter API for scholarly identifiers. Resolves DOI, PMID, ISBN, arXiv IDs, and more into formatted citations and reference-manager export formats.

Scholar Sidekick resolves scholarly identifiers into normalized bibliographic metadata and formatted citations. It supports multiple citation styles and export formats for integration with reference managers and research workflows.

## Supported Identifier Types

- DOI (e.g., 10.1038/nphys1170)
- PMID (PubMed ID, e.g., PMID: 30049270)
- PMCID (PubMed Central ID)
- ISBN (e.g., 9780192854087)
- ISSN / eISSN
- arXiv ID (e.g., arXiv:2301.07041)
- ADS bibcode (NASA Astrophysics Data System)
- WHO IRIS URL

## API Base URL

https://scholar-sidekick.com

## Authentication

Requests may include an API key via the `X-Scholar-API-Key` header. The API is also available on RapidAPI using the `X-RapidAPI-Key` header. Anonymous access is available with rate limits.

## Endpoints

### POST /api/format
Resolve one or more identifiers and return formatted citations.

Request body (JSON):
- `text` (string): A single identifier or free-text string containing identifiers.
- OR `lines` (string[]): An array of identifiers to resolve in batch.
- `style` (string, optional): Citation style ID. Builtin styles: vancouver, ama, apa, ieee, cse. Also supports thousands of CSL styles (e.g., harvard, chicago, nature, lancet). Defaults to vancouver.
- `output` (string, optional): "json" or "text". Defaults to json.

Response (200, JSON):
- `citation`: Formatted citation string (HTML or plain text).
- `styleUsed`: The style that was actually applied.
- `items`: Array of resolved CSL-JSON bibliographic items.

### POST /api/format/stream
Streaming variant of /api/format. Returns NDJSON (one JSON object per line) via `application/x-ndjson`. Useful for large batch requests.

Request body (JSON):
- `lines` (string[]): Array of identifiers.
- `style` (string, optional): Citation style ID.

### POST /api/export
Export resolved citations in reference-manager-friendly formats.

Request body (JSON):
- `text` (string) OR `items` (CSL-JSON[]): Input identifiers or pre-resolved items.
- `format` (string, required): One of: txt, ris, bibtex, csl-json, endnote-xml, refworks, nbib, rdf, csv.
- `style` (string, optional): Citation style ID.

Response: Plain text body in the requested format.

### POST /api/format-items
Format pre-resolved CSL-JSON items without re-resolving identifiers.

Request body (JSON):
- `items` (CSL-JSON[]): Array of CSL-JSON bibliographic items.
- `style` (string, optional): Citation style ID.
- `output` (string, optional): "json" or "text".

### GET /api/csl/styles
Discover available CSL citation styles. Supports search and pagination via query parameters.

### GET /api/health
Service liveness check. Returns `{ "status": "ok", "time": "<ISO timestamp>" }`.

### POST /api/retraction-check
Check a single work's retraction / correction / expression-of-concern status, sourced from Crossref `updated-by` (Retraction Watch).

Request body (JSON):
- `id` (string, required): A DOI, PMID, PMCID, arXiv ID, or ADS bibcode (non-DOI inputs are resolved to a DOI before lookup).

Response (200, JSON): the resolved DOI, the source identifier (when different), and a `result` object (or `null` when no DOI could be resolved).

### POST /api/oa-check
Check a single work's open-access status, sourced from Unpaywall.

Request body (JSON):
- `id` (string, required): A DOI or other identifier (resolved to a DOI before lookup).

Response (200, JSON): OA status (gold/green/hybrid/bronze/closed), the best legal landing/PDF URL, license, and version when available.

### POST /api/verify
Check whether a *claimed* citation matches the record at its identifier — catches the dominant fabrication pattern (real DOI + invented title) that a plain lookup misses.

Request body (JSON):
- `claimed` (object, required): a claimed citation with one identifier, e.g. `{ "title": "...", "authors": [{ "family": "..." }], "year": 2026, "container": "...", "doi": "..." }`.

Response (200, JSON): `verdict` (`matched | mismatch | ambiguous | not_found | parsing_error`), a `confidence` tier (`high | medium | low`), and a per-field similarity diff. Returns 200 on every produced verdict; 4xx/5xx only for protocol errors.

## Export Formats

- `ris` - Research Information Systems (compatible with EndNote, Zotero, Mendeley)
- `bibtex` - BibTeX (compatible with LaTeX, Overleaf, JabRef)
- `csl-json` - CSL-JSON (raw structured metadata)
- `endnote-xml` - EndNote XML
- `refworks` - RefWorks tagged format
- `nbib` - NBIB / MEDLINE format
- `rdf` - Bibliographic RDF
- `csv` - Comma-separated values
- `txt` - Formatted plain text citation

## Rate Limiting

The API uses sliding-window rate limiting. Rate limit status is communicated via standard headers: `X-RateLimit-Limit`, `X-RateLimit-Remaining`, `X-RateLimit-Reset`, `Retry-After`. Plan tiers: anonymous, free, pro, ultra, mega.

## Error Responses

Errors return JSON: `{ "ok": false, "code": "<ERROR_CODE>", "error": "<message>" }`

Common codes: BAD_REQUEST (400), UNAUTHORIZED (401), RATE_LIMITED (429), MAINTENANCE (503).

## OpenAPI Specification

Full OpenAPI 3.1 spec: https://scholar-sidekick.com/openapi/openapi.yml

Also exposed under the canonical discovery path: https://scholar-sidekick.com/.well-known/openapi.yaml

## Provenance & determinism

Scholar Sidekick exposes machine-readable provenance and reproducibility metadata at canonical `.well-known` paths so AI agents can verify data sources, fallback order, and output stability before integrating.

- Data source manifest (resolver chain, fallback order, network safety, `transform_version`): https://scholar-sidekick.com/.well-known/sources.json
- ChatGPT / agent plugin manifest (points at the OpenAPI spec): https://scholar-sidekick.com/.well-known/ai-plugin.json
- OpenAPI 3.1 spec at the discovery path: https://scholar-sidekick.com/.well-known/openapi.yaml
- API catalog (RFC 9727 linkset): https://scholar-sidekick.com/.well-known/api-catalog
- MCP server card (SEP-1649): https://scholar-sidekick.com/.well-known/mcp/server-card.json (also at https://scholar-sidekick.com/.well-known/mcp)
- Agent skills discovery index (with SHA-256 digests): https://scholar-sidekick.com/.well-known/agent-skills/index.json
- Agent discovery card (skills mapped to REST + MCP, identifiers, formats, auth, links): https://scholar-sidekick.com/.well-known/agent-card.json (also at https://scholar-sidekick.com/.well-known/agent.json)
- Machine-readable pricing: https://scholar-sidekick.com/pricing.md

Every API response includes the `x-scholar-transform-version` header. Identical inputs (identifier + style + format) at a fixed `transform_version` produce byte-identical output. The constant is bumped when normalisation, formatter, or resolver-chain changes could alter that.

Self-verification kit (copy-paste curl commands that prove the determinism, provenance, and edge-case claims): https://scholar-sidekick.com/verification (markdown: https://scholar-sidekick.com/verification.md)

Changelog (transform_version / verify_version bumps, each tagged output-affecting, verdict-affecting, breaking, or non-breaking): https://scholar-sidekick.com/changelog (markdown: https://scholar-sidekick.com/changelog.md)

## Documentation

- [Full content (all pages)](https://scholar-sidekick.com/llms-full.txt): Single-file aggregation of all site pages
- [API Docs](https://scholar-sidekick.com/docs.md): Endpoints, parameters, headers, caching, rate limits
- [MCP Server Setup](https://scholar-sidekick.com/mcp.md): Install and configure the MCP server for Claude, Cursor, and others
- [Agent Skills (skills.sh)](https://skills.sh): Install the Scholar Sidekick agent skills for Claude Code, Codex, Cursor, OpenClaw, and other agents — `npx skills add mlava/scholar-sidekick-skills` (the zero-install `scholar-sidekick-api` REST skill plus the `scholar-sidekick-mcp` skill)
- [Browser Extension](https://scholar-sidekick.com/extension): Free Chrome / Firefox / Edge extension. Right-click any DOI, PMID, PMCID, ISBN, arXiv ID, ADS bibcode, or scholarly URL on any web page to format it as a citation in Vancouver, APA, AMA, IEEE, CSE, or any of 10,000+ CSL styles
- [Integrations](https://scholar-sidekick.com/integrations) ([markdown](https://scholar-sidekick.com/integrations.md)): First-party integrations that bring Scholar Sidekick's identifier-first citation formatting, retraction checks, and open-access lookup into the notes and reference workflows you already use. Currently: Obsidian (live in the community plugins store).
- [Obsidian plugin](https://scholar-sidekick.com/integrations/obsidian) ([markdown](https://scholar-sidekick.com/integrations/obsidian.md)): Paste a DOI, PMID, ISBN, arXiv ID, ADS bibcode, or PMCID in an Obsidian note and replace it with a formatted citation. Eleven commands: format selection, replace at caret, insert via modal, per-note BibTeX / RIS export, retraction and open-access checks, single-citation verifier. Vancouver, APA, AMA, IEEE, CSE plus 10,000+ CSL styles. Free, no API key, listed in the Obsidian community plugins store.
- [Help & Limits](https://scholar-sidekick.com/help.md): Supported identifiers, styles, exports, caching, and rate limits
- [Scholarly Glossary](https://scholar-sidekick.com/glossary.md): Plain-language definitions of DOI, PMID, BibTeX, RIS, CSL, open access, retraction, and other terms
- [Scholar Sidekick Explainer](https://scholar-sidekick.com/explainer.md): A moment-of-need citation formatter - what it is, what it isn't, when it's useful.
- [Agent Guide](https://scholar-sidekick.com/AGENTS.md): Integration guide for coding agents (MCP + REST)
- [Sitemap](https://scholar-sidekick.com/sitemap.md): Full site map for agents
- [API Terms](https://scholar-sidekick.com/legal/api-terms): Terms of use for the API

## Comparisons

Honest, source-cited comparisons of Scholar Sidekick against adjacent reference managers and citation APIs. Each page sets out where the alternative wins, where Scholar Sidekick wins, and how to use both together.

- [Comparisons index](https://scholar-sidekick.com/compare) ([markdown](https://scholar-sidekick.com/compare.md)): All available comparisons
- [Best AI Citation Verifier in 2026](https://scholar-sidekick.com/compare/best-ai-citation-verifier) ([markdown](https://scholar-sidekick.com/compare/best-ai-citation-verifier.md)): Honest comparison of ten AI citation verifiers that catch fabricated DOIs and hallucinated references (Scholar Sidekick, Citely, CiteTrue, GPTZero Source Finder, Sourcely, TrueCitation, AiCitationChecker, CiteMe, SwanRef, CiteSure). Per-tool capsules, feature matrix, realistic systematic-review workflow.
- [Scholar Sidekick vs Zotero](https://scholar-sidekick.com/compare/scholar-sidekick-vs-zotero) ([markdown](https://scholar-sidekick.com/compare/scholar-sidekick-vs-zotero.md)): Reference manager vs stateless citation API. Written by a longtime Zotero user.
- [Scholar Sidekick vs ZoteroBib](https://scholar-sidekick.com/compare/scholar-sidekick-vs-zoterobib) ([markdown](https://scholar-sidekick.com/compare/scholar-sidekick-vs-zoterobib.md)): In-browser bibliography builder vs stateless citation API plus nine free tools. Written by a longtime ZoteroBib user.
- [Scholar Sidekick vs Scribbr](https://scholar-sidekick.com/compare/scholar-sidekick-vs-scribbr) ([markdown](https://scholar-sidekick.com/compare/scholar-sidekick-vs-scribbr.md)): Source-accuracy vs style-accuracy. Scribbr's Knowledge Base and expert-verified style examples vs Scholar Sidekick's live Crossref / PubMed / DataCite metadata, retraction-awareness, and deterministic transform versioning.
- [Citation MCP Servers Compared](https://scholar-sidekick.com/compare/citation-mcp-servers) ([markdown](https://scholar-sidekick.com/compare/citation-mcp-servers.md)): Honest roundup of the five citation MCP servers AI assistants currently cite: zotero-mcp, CiteAssist, citecheck, OneCite, and Scholar Sidekick MCP. Per-tool capsules, where each wins, and how to use them together.
- [Scholar Sidekick vs EndNote](https://scholar-sidekick.com/compare/scholar-sidekick-vs-endnote) ([markdown](https://scholar-sidekick.com/compare/scholar-sidekick-vs-endnote.md)): Stateless citation API and nine free tools vs Clarivate's enterprise reference manager. Cite-While-You-Write and group libraries are EndNote's home turf; Scholar Sidekick covers free identifier-first formatting, retraction checks, and a public API EndNote does not have.
- [Scholar Sidekick vs MyBib](https://scholar-sidekick.com/compare/scholar-sidekick-vs-mybib) ([markdown](https://scholar-sidekick.com/compare/scholar-sidekick-vs-mybib.md)): Identifier-first registry resolution vs URL-first in-browser bibliography builder. Both free, both built on citeproc-js, different optimisations: MyBib for in-browser student-essay workflow on URL inputs; Scholar Sidekick for authoritative-registry metadata, retraction checks, broader identifier coverage, and a public API.
- [Scholar Sidekick vs Cite This For Me](https://scholar-sidekick.com/compare/scholar-sidekick-vs-citethisforme) ([markdown](https://scholar-sidekick.com/compare/scholar-sidekick-vs-citethisforme.md)): Friction-free identifier-first API vs URL-paste in-browser bibliography. Cite This For Me's free tier covers many CSL styles but goes through click-throughs, a slow style menu, and frequent plagiarism-check prompts; Word .docx export is Premium. Written from years of personal Cite This For Me use.

## Example Usage

Resolve a DOI to a Vancouver-style citation:

```
POST /api/format
Content-Type: application/json

{ "text": "10.1056/nejmoa2033700", "style": "vancouver", "output": "text" }
```

Export multiple identifiers as BibTeX:

```
POST /api/export
Content-Type: application/json

{ "lines": ["10.1038/nphys1170", "PMID: 30049270"], "format": "bibtex" }
```

## Optional

- [Privacy Policy](https://scholar-sidekick.com/legal/privacy): Data handling, minimal logs, and scrubbed telemetry
- [Accessibility](https://scholar-sidekick.com/accessibility): WCAG compliance statement and known limitations
- [Engineering Principles](https://scholar-sidekick.com/engineering-principles) ([markdown](https://scholar-sidekick.com/engineering-principles.md)): Design philosophy - determinism, contract stability, spec fidelity, edge-case behaviour, reproducibility via `transform_version`
- [Verification](https://scholar-sidekick.com/verification) ([markdown](https://scholar-sidekick.com/verification.md)): Copy-paste curl commands that independently verify reproducibility, provenance headers, and edge-case behaviour against the live API
- [Changelog](https://scholar-sidekick.com/changelog) ([markdown](https://scholar-sidekick.com/changelog.md)): Public record of `transform_version` and `verify_version` bumps, each tagged output-affecting, verdict-affecting, breaking, or non-breaking, so integrators can detect drift and re-baseline pinned output
- [Citation integrity in the age of AI](https://scholar-sidekick.com/citation-integrity) ([markdown](https://scholar-sidekick.com/citation-integrity.md)): How LLM-driven citation fabrication works (1-in-277 biomedical papers per Topaz et al., Lancet 2026), why simple DOI checks miss the dominant pattern, and how the /api/verify endpoint catches it. Includes the three Lancet illustrative cases verbatim, the CITADEL→Scholar Sidekick methodology mapping, an inline verifier demo, and a measured 20/20 precision/recall validation set with downloadable JSON receipts.
- [AI evaluator bias in citation-tool recommendations](https://scholar-sidekick.com/citation-integrity/ai-evaluator-bias) ([markdown](https://scholar-sidekick.com/citation-integrity/ai-evaluator-bias.md)): Observation post documenting that four major AI search engines (Perplexity, Google AI, ChatGPT, Grok), asked on the same day to recommend citation infrastructure, all omitted a verifiable identifier-first option and admitted the omission when pushed - then articulated four different framings of the same structural bias (incumbency, single-purpose categories, primitive building blocks, well-established widely-known tools). Includes verbatim admissions from all four vendors with shareable conversation links, a tool-agnostic criteria checklist for evaluating any citation tool an AI recommends, and a methodology section with the 2-vs-2 retrieval-grounding split that argues the bias is architectural to recommendation logic rather than a RAG artifact.
- [Citation Verifier (web tool)](https://scholar-sidekick.com/tools/citation-verifier) ([markdown](https://scholar-sidekick.com/tools/citation-verifier.md)): User-facing single-citation verifier. Paste a title + identifier (DOI, PMID, PMCID, arXiv, ISBN, ISSN, ADS, WHO IRIS); see verdict (matched / mismatch / ambiguous / not_found), per-field similarity diff, candidate matches from title-search, and full provenance. Same backend as POST /api/verify and the scholar-sidekick MCP `verifyCitation` tool.
- [DOI to BibTeX](https://scholar-sidekick.com/tools/doi-to-bibtex) ([markdown](https://scholar-sidekick.com/tools/doi-to-bibtex.md)): Single-identifier DOI/PMID/PMCID/ISBN/arXiv/ISSN/ADS/WHO IRIS to BibTeX entry. Backend: POST /api/export, format=bibtex.
- [DOI to RIS](https://scholar-sidekick.com/tools/doi-to-ris) ([markdown](https://scholar-sidekick.com/tools/doi-to-ris.md)): Same identifier surface, RIS output for EndNote / Zotero / Mendeley / RefWorks import.
- [DOI Lookup](https://scholar-sidekick.com/tools/doi-lookup) ([markdown](https://scholar-sidekick.com/tools/doi-lookup.md)): Resolve one identifier and inspect the structured metadata (title, authors, container, year, identifiers).
- [PMID / PMCID / DOI Converter](https://scholar-sidekick.com/tools/pubmed-id-converter) ([markdown](https://scholar-sidekick.com/tools/pubmed-id-converter.md)): Swap between PubMed identifier types (PMID, PMCID, DOI) for the same paper.
- [Identifier Detector](https://scholar-sidekick.com/tools/identifier-detector) ([markdown](https://scholar-sidekick.com/tools/identifier-detector.md)): Bulk extract every DOI / PMID / PMCID / arXiv / ISBN / ISSN / ADS bibcode from a text block.
- [Identifier Validator](https://scholar-sidekick.com/tools/identifier-validator) ([markdown](https://scholar-sidekick.com/tools/identifier-validator.md)): Single-ID well-formedness and resolvability check (no metadata fetch).
- [Citation Style Comparator](https://scholar-sidekick.com/tools/citation-style-comparator) ([markdown](https://scholar-sidekick.com/tools/citation-style-comparator.md)): Render the same paper in any of 10,000+ CSL styles side by side.
- [Open Access Checker](https://scholar-sidekick.com/tools/open-access-checker) ([markdown](https://scholar-sidekick.com/tools/open-access-checker.md)): Unpaywall-backed check for a legal free copy of a paper. Backend: POST /api/oa-check, scholar-sidekick MCP `checkOpenAccess` tool.
- [Retraction Checker](https://scholar-sidekick.com/tools/retraction-checker) ([markdown](https://scholar-sidekick.com/tools/retraction-checker.md)): Retraction Watch via Crossref check for retraction / correction / expression of concern. Backend: POST /api/retraction-check, scholar-sidekick MCP `checkRetraction` tool.
- [Explainer](https://scholar-sidekick.com/explainer): How Scholar Sidekick fits into research workflows