# /reactome/pathways/participants

`POST /api/reactome/pathways/participants`

Price: 20 credits

List the molecules taking part in one Reactome pathway or reaction

## How to use it

Participants are collected over the whole event tree below the id, not only its immediate steps, so a top-level pathway returns everything its sub-pathways touch. Cross-references come back inline in `reference_entities`, which is what you join to UniProt or ChEBI on `identifier`, but a few uncurated entities carry none, so read it as a list that can be empty; set `with_reference_entities` only when you also need the sequence, gene names and description behind them. An id Reactome does not know comes back as 412 rather than an empty list.

## Parameters

- `access-token` (string, required)

## Request body

- `timeout` (integer) — Max scrapping execution timeout (in seconds) (default: 300; min: 20; max: 1500)
- `pathway` (string, required) — Reactome stable id or numeric dbId of the event whose participants are wanted (examples: "R-HSA-9612973", "9612973", "R-HSA-109581"; minLength: 1)
- `with_reference_entities` (boolean) — Fill in the full outside-database record of every cross-reference — gene names, sequence length, description and comments — instead of its identifier and url alone (default: false)
- `count` (integer, required) — Max number of results (min: 1)

## Response

### 200 — Successful Response

- `@type` (string) (default: "ReactomeParticipant")
- `id` (string, required)
- `db_id` (integer, nullable)
- `display_name` (string) (default: "")
- `names` (array) (default: [])
- `st_id_version` (string) (default: "")
- `species_name` (string) (default: "")
- `schema_class` (string) (default: "")
- `display_class` (string) (default: "")
- `max_depth` (integer, nullable)
- `systematic_name` (string) (default: "")
- `reference_type` (string) (default: "")
- `start_coordinate` (integer, nullable)
- `end_coordinate` (integer, nullable)
- `is_chimeric` (boolean, nullable)
- `in_disease` (boolean, nullable)
- `reference_entities` (array) (default: [])
  - `@type` (string) (default: "ReactomeReferenceEntity")
  - `id` (integer, required)
  - `st_id` (string) (default: "")
  - `display_name` (string) (default: "")
  - `database_name` (string) (default: "")
  - `identifier` (string) (default: "")
  - `secondary_identifier` (array) (default: [])
  - `other_identifier` (array) (default: [])
  - `variant_identifier` (string) (default: "")
  - `names` (array) (default: [])
  - `gene_names` (array) (default: [])
  - `description` (array) (default: [])
  - `comment` (array) (default: [])
  - `keyword` (array) (default: [])
  - `molecule_type` (string) (default: "")
  - `formula` (string) (default: "")
  - `checksum` (string) (default: "")
  - `sequence_length` (integer, nullable)
  - `chain` (array) (default: [])
  - `is_sequence_changed` (boolean, nullable)
  - `schema_class` (string) (default: "")
  - `display_class` (string) (default: "")
  - `url` (string) (default: "")
- `url` (string) (default: "")

## Errors

### 422 — Validation Error

Not a Reactome identifier

What to do: Check the fields against this schema. A URN with the wrong prefix is the most common cause.

- `detail` (array)
  - `loc` (array, required)
  - `msg` (string, required)
  - `type` (string, required)
  - `input` (any)
  - `ctx` (object)

### 408

The request ran past its time limit

What to do: Raise `timeout` in the request body, up to the maximum this endpoint documents. Lowering `count` or turning off the `with_*` flags also helps, because less work finishes sooner.

### 412

No participants for this id

What to do: Retrying will not help: either the entity does not exist, or the input points at a different one.

### 429

Too many requests: a rate limit or a usage window is exhausted

What to do: When the response carries an X-Retry-After header, wait that many seconds and retry: the same number is in the body as `detail.retry_after`, and the limit clears once that window passes. The message in the body names the limit that was hit.

### 500

Something broke on our side

What to do: Retrying will not help. If it keeps happening, send us the X-Request-ID from the response headers.

### 529

Rate limit reached, or the endpoint is overloaded

What to do: Wait at least 30 seconds, then retry.

## Response envelope

Success: Array of objects (may be empty if no results)

Error: Error may coexist with partial results if it occurs mid-execution. Check X-Error header and status code.

Every response carries these headers:

- `X-Error` — Error message text (present only on error)
- `X-Request-ID` — Unique request identifier
- `X-Execution-Time` — Execution time in seconds
- `X-Result-Count` — How many records the body carries. 0 means an empty result, which is a normal answer and not by itself an error. A non-zero count can come back together with X-Error when the failure happened partway through — read this header and X-Error independently.
- `X-Total-Available-Results` — How many records exist for this query, when the endpoint can say. On a `dry_run` request this is the answer and the body is empty. It saturates: the endpoint's documented maximum means 'at least that many', any smaller number is exact.
- `X-Warning` — Present when the request body carried keys this endpoint does not document. They were ignored, so any filter you meant to apply through them did not apply. Check the spelling against this schema and retry.
- `X-Retry-After` — Seconds to wait before retrying. Present only on 429.