REST API Documentation

Base URL: https://pkaatlas.com

All endpoints below use GET and can be accessed without an API key. Responses are JSON, except structure images (SVG) and record exports (CSV).

URL-encode SMILES and other parameter values containing characters such as #, + or &. Search results contain records; one compound may have multiple measurements.

Version and audit endpoints

curl "https://pkaatlas.com/api/v1/release" Open example

Inspect a source record and its representative membership:

curl "https://pkaatlas.com/api/v1/record/49ada355a6a2:2" Open example

Search the complete archive, including quarantined and unresolved rows:

curl "https://pkaatlas.com/api/v1/search?scope=all&limit=10" Open example

GET /api/v1/search

Search pKa measurements by compound, pKa range, solvent, or quality grade.

Parameters

Default scope: representatives (149,189 records). Use scope=all (174,082), scope=eligible (150,994), or scope=quarantine (23,088). Use entity_kind=structure_defined|protein_site_context|unresolved_record to filter an identity class. Every result includes source_row_id, candidate_record_id, qc_status, exclude_reason and review annotations. Count definitions and complete downloads.

Parameter	Type	Description	Example
`q`	string	SMILES, stored identifier, reference, dataset name, or available natural-product name/class. Name coverage depends on the source.	`?q=CCO`
`smiles`	string	Exact parsed canonical structure match	`?smiles=CCO`
`inchi_key`	string	Exact match to a non-null `inchi_key` returned by this API; availability depends on the source.	Use a value from a returned record.
`pka_min`	float	Minimum pKa value	`?pka_min=3.0`
`pka_max`	float	Maximum pKa value	`?pka_max=7.0`
`solvent`	string	Filter by solvent	`?solvent=water`
`confidence`	string	Comma-separated quality grades: Grade A, Grade B, Grade C, Grade D (API values: A,B,C,D)	`?confidence=A,B`
`data_type`	string	experimental / predicted	`?data_type=experimental`
`temperature_min`	float	Minimum temperature in °C; records without temperature are excluded.	`?temperature_min=20`
`temperature_max`	float	Maximum temperature in °C	`?temperature_max=30`
`pka_type`	string	Exact pKa type as stored in a record	`?pka_type=pKaH1`
`reference`	string	Exact reference code	`?reference=B29`
`dataset_name`	string	Exact source dataset name	`?dataset_name=IUPAC_high_confidence_v2.3`
`limit`	int	Measurements per page: use 1–500; default 50.	`?limit=50`
`offset`	int	Number of records to skip; use a non-negative value, default 0.	`?offset=0`

Example

curl "https://pkaatlas.com/api/v1/search?pka_min=3&pka_max=7&solvent=water&confidence=A,B&limit=20" Open example

Response fields: total, limit, offset, page, total_pages, has_next, has_prev and results. Use each result's compound_id for compound details.

GET /api/v1/compound/<id>

Get full compound information with all pKa measurements.

Example

curl "https://pkaatlas.com/api/v1/compound/42" Open example

Returns compound and measurements. An unknown ID returns HTTP 404.

GET /api/v1/stats

Get database statistics, solvent distribution, and NP distribution.

Example

curl "https://pkaatlas.com/api/v1/stats" Open example

Returns stats, solvent_distribution and np_distribution for the current online dataset.

GET /api/v1/compounds/count

Quick endpoint to get total compound count.

Example

curl "https://pkaatlas.com/api/v1/compounds/count" Open example

Current Response

Loading current compound count…

GET /api/v1/substructure

Retrieve matching structures using RDKit with fingerprint pre-screening, up to the requested result limit.

Parameter	Type	Description
`smiles`	string (required)	Query SMILES. The examples use SMILES; SMARTS support is limited.
`max_results`	int	Max hits (default 100, max 500)
`include_pka`	optional	Set to `1` to include pKa range and measurement count. Omit this parameter to leave these fields out.

Example

curl "https://pkaatlas.com/api/v1/substructure?smiles=c1ccccc1O&max_results=50&include_pka=1" Open example

Returns query_smiles, total_hits, max_results and results. total_hits counts returned hits and is subject to the result limit. Missing or invalid query SMILES returns HTTP 400.

GET /api/v1/similarity

Similarity search — Morgan2 fingerprint Tanimoto similarity.

Parameter	Type	Description
`smiles`	string (required)	Query SMILES
`threshold`	float	Minimum Tanimoto similarity, 0–1; default 0.4.
`max_results`	int	Maximum returned hits: default 50, max 200.

Example

curl "https://pkaatlas.com/api/v1/similarity?smiles=CCO&threshold=0.6" Open example

Results are sorted by descending similarity. Missing or invalid query SMILES returns HTTP 400.

GET /api/v1/image/<smiles>

Generate 2D structure SVG image from SMILES or compound ID.

Parameter	Type	Description
`width`	int	Image width (default 400)
`height`	int	Image height (default 200)
`highlight`	string	SMILES substructure to highlight in red

Examples

curl "https://pkaatlas.com/api/v1/image/CCO?width=300&height=150" Open example

curl "https://pkaatlas.com/api/v1/image/compound/42?width=500&height=250" Open example

curl "https://pkaatlas.com/api/v1/image/c1ccccc1O?highlight=c1ccccc1" Open example

Response type: image/svg+xml. A structure that cannot be rendered produces an SVG error message.

GET/api/v1/export

Download filtered source or representative records as UTF-8 CSV. For an uncapped complete layer, use full compressed downloads.

Supported filters: q, smiles, pka_min, pka_max, solvent, confidence, data_type, temperature_min, temperature_max and pka_type. limit defaults to 10,000 and is capped at 50,000 records. Use offset to continue after any non-negative number of matching rows. All search filters, including scope, entity_kind, np_only, inchi_key, reference and dataset_name, are supported.

curl "https://pkaatlas.com/api/v1/export?solvent=DMSO&limit=100" Open example

To save the file from a terminal, append -o pkaatlas_DMSO.csv to the command. Headers X-Total-Count, X-Exported-Count and X-Dataset-Version identify the result size and version. Original full fields remain in the complete archives.

GET/api/v1/structure/stats

Check structure-search readiness. total_compounds counts structures available to RDKit and can be lower than the database compound count; ready indicates initialization status.

curl "https://pkaatlas.com/api/v1/structure/stats" Open example

GET/api/v1/provenance

Get the source-compilation registry, keyed by dataset name. Registry entry counts describe the source compilations and may differ from counts retained in the online dataset.

curl "https://pkaatlas.com/api/v1/provenance" Open example

GET/api/v1/provenance/<dataset_name>

Get compilation metadata and provenance information for an exact dataset name. An unknown name returns HTTP 404.

curl "https://pkaatlas.com/api/v1/provenance/IUPAC_high_confidence_v2.3" Open example

GET/api/v1/documents

Get the document registry as total and documents. This endpoint returns document metadata.

curl "https://pkaatlas.com/api/v1/documents" Open example

GET/health

Get service status, timestamp, loaded compound and measurement counts, and RDKit readiness.

curl "https://pkaatlas.com/health" Open example

Quick Test

Click a button to send a GET request to https://pkaatlas.com.