← API reference
Structure prediction · Protein Design

Chai-1 API

Predict protein or protein-ligand complex structures with Chai-1.

Builds Chai's typed FASTA input and runs the official chai-lab folding CLI.

Web form Home page ↗ Source code ↗
Submit POST /api/chai1/

Queues a run and returns 202 with the job.

Schema GET /api/chai1/

Returns this tool's metadata and the fields below, as JSON.

Runtime

Linux and a CUDA GPU with bfloat16 support are required; model weights download on first use · Python app (uv) · Expensive (min or hours)

License

Permissive. Apache 2.0 for both the code and the model weights; upstream states this covers commercial use including drug discovery. Earlier releases used the narrower Chai Discovery Community Licence.

Tasks

Pick a mode with task

Fields belonging to another task are ignored, so send only the ones for the task you chose.

taskMode
sequence default Sequence
list Chain list
molecules Molecules (JSON)
Request body

Fields

The same names the web form posts. See the field type table for what each kind means over HTTP.

Name Type Required Default Description
job_name string text no chai1-demo Job name
sequence_molecules sequence string (JSON array) molecule_builder yes [{"type": "protein", "sequence": "MSTNPKPQRKTKRNTNRRPQDVKFPGG", "cyclic": false, "modifica … Molecules Add one box per chain: Protein, Ligand, DNA, or RNA. Ligands take a SMILES string (Chai-1 does not accept CCD codes). A modification applies a CCD residue code at a given position. Chai-1 does not support cyclic chains. One of: protein, ligand, dna, rna. A JSON array, sent as a string. See molecule entries.
proteins list string textarea yes MSTNPKPQRKTKRNTNRRPQDVKFPGG Protein chains One protein chain sequence per line.
dnas list string textarea no — DNA chains (optional) One DNA chain sequence per line.
rnas list string textarea no — RNA chains (optional) One RNA chain sequence per line.
molecules molecules string textarea yes [{"type": "protein", "chain": "A", "sequence": "MSTNPKPQRKTKRNTNRRPQDVKFPGG"}] Molecules JSON list of {"type": "protein"|"dna"|"rna", "chain": "A", "sequence": "..."}.
ligands list molecules string textarea no — Ligands (optional) One ligand SMILES per line.
use_msa_server boolean checkbox no false Use the public MSA server Opt in to a network call to ColabFold's MMseqs2 server for better accuracy.
use_templates_server boolean checkbox no false Use the public pdb100 template server
pocket_restraints string textarea no — Pocket restraints (optional) JSON list, e.g. [{"chainA":"A","res_idxA":1,"chainB":"B"}] (any residue on chainB near residue res_idxA on chainA).
contact_restraints string textarea no — Contact restraints (optional) JSON list, e.g. [{"chainA":"A","res_idxA":1,"chainB":"B","res_idxB":1}].
covalent_restraints string textarea no — Covalent restraints (optional) JSON list, e.g. [{"chainA":"A","res_idxA":1,"covalentAtomA":"C","chainB":"B","res_idxB":1,"covalentAtomB":"C"}]. Chai-1 was not trained on intra-chain bonds; use inter-chain pairs.
restraints_min_distance number number no 0 Restraints minimum distance, angstrom minimum 0, maximum 20, step 0.1.
restraints_max_distance number number no 5 Restraints maximum distance, angstrom minimum 0, maximum 20, step 0.1.
num_samples number number no 5 Diffusion samples minimum 1, maximum 25.
num_trunk_samples number number no 1 Trunk samples minimum 1, maximum 10.
num_recycles number number no 3 Recycles minimum 1, maximum 20.
num_diffn_timesteps number number no 200 Diffusion timesteps minimum 10, maximum 1000.
seed number number no 0 Random seed minimum 0, maximum 2147483647.

Molecule entry keys

KeyMeaning
type Which of the field's molecule types this entry is.
sequence The residues, for a protein, dna, or rna entry.
ligand A SMILES string or a CCD_ code, for a ligand entry.
ion An ion code, for an ion entry.
cyclic Whether a polymer chain is cyclic. Tools that cannot model one reject it rather than ignoring it.
modifications Substitutions, as {"position": <1-indexed integer>, "residue": "<CCD code>"} objects.
Example

A request that runs

These are the defaults, exactly as the web form would post them.

curl -X POST https://www.athanortools.com/api/chai1/ \
  -H 'Content-Type: application/json' \
  -d '{
  "task": "sequence",
  "job_name": "chai1-demo",
  "sequence_molecules": "[{\"type\": \"protein\", \"sequence\": \"MSTNPKPQRKTKRNTNRRPQDVKFPGG\", \"cyclic\": false, \"modifications\": []}]",
  "use_msa_server": false,
  "use_templates_server": false,
  "pocket_restraints": "",
  "contact_restraints": "",
  "covalent_restraints": "",
  "restraints_min_distance": 0,
  "restraints_max_distance": 5,
  "num_samples": 5,
  "num_trunk_samples": 1,
  "num_recycles": 3,
  "num_diffn_timesteps": 200,
  "seed": 0
}'

The reply is 202 with a queued job; poll its status_url until status is succeeded or failed. See the quick start for the whole exchange.

Responses

What comes back

statusMeaning
queued Accepted, waiting for the jobs ahead of it. `position` counts how many those are.
running The tool is executing now.
succeeded Finished; `result` holds the tool's output and `license` the terms it came under.
failed Finished; `error` holds a code and a message.

Errors

codeMeaning
invalid_input The client supplied invalid or incomplete input.
tool_unavailable The requested third-party dependency is not available on this host.
execution_failed A configured third-party process exited unsuccessfully.
internal_error An adapter failed in a way it does not describe. The detail is in the server log, not the response.
not_found No job has that id. Finished jobs are dropped eventually.