Teach the model to call your APIs
Describe your private API as a skill, fine-tune the model on when and how to call it, and Harness bounds every call with scopes and an audit trail.
{
"type": "tool_use",
"name": "lookup_order",
"input": { "order_id": "SO-4471" }
}
# the model asked; Harness checked the key's scopeSkills carry the contract
A skill definition holds the endpoint, the authentication, the parameters and the schema, so the model knows what it may call and what the call returns.
Fine-tuning teaches judgement
The model learns from examples when to reach for a skill and how to populate its parameters, so tool calls follow the patterns your data carries.
Harness bounds every call
The same four gates that govern every request check the scope on the key before a tool call executes, and the call lands in the audit trail.
From skill to tool call
A skill definition carries the HTTP method, the endpoint, the authentication pattern, the parameters with their types and the response schema. The model reads the definition at inference time, so adding a skill is a data change with no retraining.
Results from LLMs powered by Nucleus
monthly revenue re-attributed in marketing
rerouted in a single fleet optimisation
of downtime prevented in manufacturing
prediction accuracy on equipment failures
Models that call the tools your teams use
47 trucks rerouted while they were still moving
Every incident past its four-hour SLA, escalated by name
Line 3's next failure, booked into the maintenance window
What tool use includes
Skills
- Define skills as structured JSON
- HTTP method, endpoint, auth, parameters and schema
- Add or update a skill with no retraining
- Response schema validates what the model returns
Training
- Fine-tune on tool-call examples in JSONL
- Positive and negative examples teach judgement
- Same training meters, same base model pricing
- 25 open base models across six modalities
Governance
- Harness checks the infer scope on every call
- Project-bound keys limit blast radius
- Every tool call in the append-only audit trail
- Four gates: organisation, authority, project, allowed
Two meters, usage-based
Training and inference tokens
Fine-tuning jobs from $0.22 / 1M tokens. Inference from $0.15 / 1M tokens. See pricing for the full model catalogue.
Pick your path
Harness
Permissions, scoped keys and audit
On-Premise Deployment
Our GPU servers, your site
MCP
Your model in your tools
RAG
Answers from your documents
Webhooks
Signed events to your systems
Go deeper
Teach the model to call your APIs.
Describe a skill, fine-tune on examples, and let Harness govern every call.