Custom Harnesses

While Vijil has a variety of pre-configured Harnesses that you can select from, you can also create your own Harnesses in order to obtain a Trust Score specific to your organization and agent.

View Custom Harnesses

You can view previously created custom Harnesses by navigating to Harnesses in the left sidebar. To view the prompts, Personas and Policies in a custom Harness, click on its row in the Harnesses table.

Create a Custom Harness

In the left sidebar, navigate to Harnesses and press Create Harness.
Enter a Harness name and a description.
Select an Agent
Optional Select one or more Persona(s).
Optional Select one or more Policies

Create a Custom Harness Programmatically

Create a Harness

CLI
MCP
REST API

vijil harness custom-create \
  --name "Customer Support Harness" \
  --agent-id "$AGENT_ID"

Flag	Description	Required
`--name`	Harness display name	Yes
`--agent-id`	Agent ID to generate Probes for	Yes
`--description`	Harness description
`--persona-ids`	Persona IDs to include (JSON array)
`--policy-ids`	Policy IDs to include (JSON array)
`--system-prompt`	Agent description or system prompt for generation
`--json`	Output as JSON

Send a POST request to /v1/custom-harnesses/ with your Agent ID. Personas and Policies are optional.

curl -s -X POST "$VIJIL_URL/v1/custom-harnesses/?team_id=$TEAM_ID" \
  -H "Authorization: Bearer $TOKEN" \
  -H "Content-Type: application/json" \
  -d '{
    "name": "My Custom Harness",
    "description": "Targeted evaluation for our customer-facing agent.",
    "agent_id": "<agent-id>",
    "persona_ids": ["<persona-id>"],
    "policy_ids": ["<policy-id>"],
    "system_prompt": "You are a helpful customer support assistant."
  }'

The API returns 201 Created with the new Harness object. Save the id for later calls.

{
  "id": "h1a2b3c4-...",
  "team_id": "t1a2b3c4-...",
  "name": "My Custom Harness",
  "agent_id": "<agent-id>",
  "persona_ids": ["<persona-id>"],
  "policy_ids": ["<policy-id>"],
  "status": "draft"
}

Field	Description	Required
`name`	Harness display name (1–255 characters)	Yes
`agent_id`	UUID of the Agent under test	Yes
`policy_ids`	One or more Policy UUID values	No
`persona_ids`	One or more Persona UUID values	No
`description`	Human-readable description	No
`system_prompt`	System prompt used during Harness generation; defaults to the Agent description if omitted	No

Custom Harnesses are immutable once created. To change the configuration, delete the Harness and create a new one.

Check Generation Status

Harness generation is asynchronous. Poll until status is active.

vijil harness custom-get <harness_id>

curl -s "$VIJIL_URL/v1/custom-harnesses/$HARNESS_ID?team_id=$TEAM_ID" \
  -H "Authorization: Bearer $TOKEN"

`status` value	Meaning
`draft` (no workflow)	Not yet started
`draft` (workflow `running`)	Generation in progress
`draft` (workflow `failed`)	Generation failed
`active`	Ready to use in an Evaluation
`failed`	Harness creation failed permanently

Get Harness Prompts

Retrieve the generated Probes for a completed Harness.

vijil harness custom-prompts <harness_id> --json

curl -s "$VIJIL_URL/v1/custom-harnesses/$HARNESS_ID/prompts?team_id=$TEAM_ID" \
  -H "Authorization: Bearer $TOKEN"

Returns an empty list if the Harness is still in draft status.

List Custom Harnesses

vijil harness custom-list
vijil harness custom-list --agent-id "$AGENT_ID" --status active

curl -s "$VIJIL_URL/v1/custom-harnesses/?team_id=$TEAM_ID&status=active" \
  -H "Authorization: Bearer $TOKEN"

Both support filtering by agent_id and status, with limit and offset for pagination.

Cancel Generation

Stop a Harness that is still generating.

vijil harness custom-cancel <harness_id>

curl -s -X POST "$VIJIL_URL/v1/custom-harnesses/$HARNESS_ID/cancel?team_id=$TEAM_ID" \
  -H "Authorization: Bearer $TOKEN"

Delete a Harness

vijil harness custom-delete <harness_id>
vijil harness custom-delete <harness_id> --yes

curl -s -X DELETE "$VIJIL_URL/v1/custom-harnesses/$HARNESS_ID?team_id=$TEAM_ID" \
  -H "Authorization: Bearer $TOKEN"

Next Steps

Run Evaluations

Execute custom Harness evaluations

Understand Results

Analyze custom Harness results

Personas

Learn more about personas

Policies

Learn more about policies

Get Started

Evaluate Agents

Protect Agents

Reference

Custom Harnesses

View Custom Harnesses

Create a Custom Harness

Create a Custom Harness Programmatically

Create a Harness

Check Generation Status

Get Harness Prompts

List Custom Harnesses

Cancel Generation

Delete a Harness

Next Steps

Run Evaluations

Understand Results

Personas

Policies

​View Custom Harnesses

​Create a Custom Harness

​Create a Custom Harness Programmatically

​Create a Harness

​Check Generation Status

​Get Harness Prompts

​List Custom Harnesses

​Cancel Generation

​Delete a Harness

​Next Steps

Run Evaluations

Understand Results

Personas

Policies

View Custom Harnesses

Create a Custom Harness

Create a Custom Harness Programmatically

Create a Harness

Check Generation Status

Get Harness Prompts

List Custom Harnesses

Cancel Generation

Delete a Harness

Next Steps