---
title: "Look up a chemical compound's canonical properties from PubChem"
method: POST
path: "/v1/chemistry/compound/lookup"
tags: ["chemistry"]
---

# Look up a chemical compound's canonical properties from PubChem

`POST /v1/chemistry/compound/lookup`

## Request

- Base URL: `https://api.snipget.ai` (the document declares no server; this is the origin it was published from)
- URL: `https://api.snipget.ai/v1/chemistry/compound/lookup`
- Auth: none declared

Resolves any common identifier (name, CAS, CID, SMILES, InChI, InChIKey) to a compound and returns formula, molecular weight, IUPAC name, canonical/isomeric SMILES, InChI, InChIKey, and the PubChem CID. Backed by PubChem (NIH/NLM), Redis-cached 30 days. Unknown compound -> confidence 0.0; PubChem outage -> 503. For the full synonym list use /chemistry/synonyms. Charges 2 cost_units; 1 when the query is empty (rejected locally before PubChem is called); an unknown query_type is a request-shape error, rejected unbilled (INVALID_INPUT).

## Query parameters

- `include_receipt` boolean

## Headers

- `authorization` string, nullable
- `X-API-Key` string, nullable

## Request body

- CompoundLookupRequest
  - `query` string, required: The compound identifier to look up (e.g. 'aspirin').
  - `query_type` string: Identifier type: name, cas, cid, smiles, inchi, or inchikey. A CAS number resolves as a PubChem name synonym. Default 'name'.
  - `include_trace` boolean

## Response `200`

Successful Response

- ChemistryCompoundLookupResponse: Success envelope for `/v1/chemistry/compound/lookup` — `result` carries this utility's precise shape.
  - `status` string
  - `confidence` number, required
  - `result` object, required: Result of :func:`compound_lookup`. ``input``, ``query_type`` and ``is_valid`` are always present; the compound fields appear on a match and ``why_invalid`` on a miss.
    - `input` string, required
    - `query_type` string, required
    - `is_valid` boolean, required
    - `why_invalid` string
    - `cid` integer
    - `iupac_name` string
    - `formula` string
    - `molecular_weight` number
    - `canonical_smiles` string
    - `isomeric_smiles` string
    - `inchi` string
    - `inchikey` string
    - `source` string
  - `meta` ResponseMeta: Metadata attached to every successful response.
    - `version` string
    - `build` string
    - `elapsed_ms` integer
    - `cost_units` integer: Cost units charged for this call: one per item processed (a batch of N items = N; live-registry lookups bill 2 per item). A call is one request; cost units are the billing measure.
    - `request_id` string, nullable
    - `trace` string[], nullable
    - `rate_limit_remaining` integer, nullable
    - `rate_limit_reset` integer, nullable
    - `quota_remaining` integer, nullable: Cost units left in the plan's monthly included bucket before this call's charge lands (None on unlimited tiers).
    - `quota_reset` integer, nullable: Unix timestamp when the monthly included bucket resets.
    - `credit_remaining_usd` number, nullable: Prepaid overage-allowance balance in USD, populated once the included cost units are used up and this call is drawing on it.
    - `receipt` ReceiptMeta: Opt-in execution receipt (ADR #68 B1) — caller-verifiable hashes. Requested with the ``include_receipt=true`` query parameter (free, like ``include_trace``). Reproduce either hash with any RFC 8785 (JCS) library: ``input_hash = sha256(jcs({"tool": <request path>, "args": <your JSON body minus include_trace/include_receipt>}))``; ``result_hash = sha256(jcs(result))``. For deterministic tools (everything except the generators) the same input on the same ``build`` reproduces ``result_hash`` — disputes are honored by replay.
      - `receipt_id` string, required
      - `build` string, required
      - `input_hash` string, nullable
      - `result_hash` string, nullable
      - `error` string, nullable
      - `message` string, nullable

## Other responses

- `400`: Input was syntactically valid but semantically unusable (`INVALID_INPUT`). Not retryable without changing the input.
- `401`: Missing or unrecognized API key. Send it as `Authorization: Bearer <key>` or `X-API-Key: <key>`. Keys are issued at https://snipget.ai.
- `403`: The key is valid but this caller may not use it: the request IP is outside the key's allowlist (`IP_NOT_ALLOWED`) or the account is deactivated (`ACCOUNT_DEACTIVATED`).
- `422`: The request body failed schema validation (`INVALID_REQUEST`). `details` lists the per-field errors. Not retryable without changing the request.
- `429`: Two distinct conditions share this status — branch on `error_code`. **`RATE_LIMITED`** is a per-second throughput throttle: retry after `retry_after_seconds` (the precise float; the `Retry-After` header is the same value rounded up). **`QUOTA_EXCEEDED`** is monthly capacity and is NOT retryable: recovery depends on `limit_type` — upgrade (`monthly_quota`), buy an overage allowance (`included_exhausted`), or top up (`overage_balance_exhausted`).
- `503`: A transient, retryable service condition — branch on `error_code`. **`MAINTENANCE_MODE`**: an admin-toggled maintenance window (auth, portal, and webhook surfaces stay up). **`UPSTREAM_UNAVAILABLE`**: a utility's external data source (PubChem, RxNorm, ClinicalTrials.gov, the FX feed, NPPES…) is down, blocking us, or timed out. **`UPSTREAM_RATE_LIMITED`**: that external source is throttling Snipget (it returned a 429) — the caller's own rate is fine, so this is NOT our `RATE_LIMITED` (429); it's a service-side throttle. All three are retryable; wait for `retry_after_seconds` / the `Retry-After` header when present.

---

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