Composable Workflows

Martha workflows support conditional routing, LLM-based classification, sub-workflows, and parallel execution. This lets you build complex multi-step processes from simple building blocks.

This guide covers:

• Workflow designers — how to use choice, LLM router, sub-workflow, and parallel nodes
• Developers — how the executor processes these nodes and what to expect

---

Node Types

Choice Node (Conditional Routing)

A choice node evaluates a variable against a list of conditions and routes to the first matching branch.

{
  "id": "route_by_priority",
  "type": "CHOICE",
  "config": {
    "eval_variable": "{{inputs.priority}}",
    "conditions": [
      { "operator": "equals", "value": "urgent" },
      { "operator": "equals", "value": "normal" }
    ]
  }
}

The executor evaluates conditions top-to-bottom. The first match routes to branch-0, the second to branch-1, etc. If nothing matches, the default branch is taken.

Edges

Connect choice outputs to downstream nodes using source_handle:

[
  { "from": "route_by_priority", "to": "urgent_handler", "source_handle": "branch-0" },
  { "from": "route_by_priority", "to": "normal_handler", "source_handle": "branch-1" },
  { "from": "route_by_priority", "to": "fallback_handler", "source_handle": "default" }
]

Operators

Operator	Description	Example
equals	Exact string match	"urgent" matches "urgent"
not_equals	Inverse of equals
contains	Substring check	"error" matches "connection error"
not_contains	Inverse of contains
greater_than	Numeric comparison	"100" > "50"
less_than	Numeric comparison
matches_regex	Regex pattern match	"^ERR-\\d+$" matches "ERR-404"
is_empty	None, "", [], {}
is_not_empty	Inverse of is_empty

Template Values

Both eval_variable and condition value support {{...}} templates:

• {{inputs.field}} — user inputs passed to the workflow
• {{inputs.nested.path}} — nested input fields

!!! warning "Condition values cannot reference {{nodes.*}}" For security, condition values are restricted to {{inputs.*}} templates. Referencing other node outputs in conditions is not allowed.

---

LLM Router (AI Classification)

An LLM router uses an AI model to classify text input and route to the matching branch.

{
  "id": "classify_intent",
  "type": "CHOICE_LLM",
  "config": {
    "eval_variable": "{{inputs.message}}",
    "llm_config": {
      "model": "anthropic/claude-sonnet-4-5-20250929",
      "temperature": 0
    },
    "conditions": [
      { "operator": "equals", "value": "billing" },
      { "operator": "equals", "value": "support" },
      { "operator": "equals", "value": "sales" }
    ]
  }
}

The LLM receives a classification prompt with the configured categories and input text. Its response is matched against conditions using the same operators as choice nodes.

LLM Config

Field	Default	Description
model	gpt-4o-mini	Any model supported by LiteLLM
temperature	0	Lower = more deterministic classification
prompt	(built-in)	Custom classification prompt. Use {input} and {categories} placeholders.

If the LLM returns an unrecognized category, the default branch is taken. If the LLM call fails, the default branch is also taken (with an error dict).

---

Sub-Workflow (Composition)

A sub-workflow node executes another workflow as a child, with input/output mapping between parent and child.

{
  "id": "run_validation",
  "type": "SUB_WORKFLOW",
  "config": {
    "workflow_name": "validation_workflow",
    "input_mapping": {
      "document_id": "{{inputs.doc_id}}",
      "strict_mode": true
    },
    "output_mapping": {
      "validation_result": "nodes.validator.output"
    },
    "timeout_seconds": 120,
    "on_error": "abort"
  }
}

Config Fields

Field	Required	Default	Description
workflow_name	Yes	—	Name of the child workflow to execute
input_mapping	No	{}	Map parent context values to child inputs. Supports {{...}} templates.
output_mapping	No	{}	Map child result paths back to parent. Uses dot-notation (e.g., nodes.step.output).
timeout_seconds	No	300	Maximum execution time for the child workflow
on_error	No	abort	abort = propagate error, fallback = use fallback_value
fallback_value	No	{}	Value returned if on_error is fallback and the child fails

Cycle Detection

Martha prevents recursive loops. If workflow A calls workflow B which calls workflow A, the cycle is detected at runtime and returns an error:

Recursive sub-workflow detected: wf_b -> wf_a -> wf_b

Maximum nesting depth is 3 levels. Deeper nesting returns an error immediately.

---

Parallel Execution

A parallel node executes multiple branches concurrently and merges results.

Edge-Based Branches (Recommended)

Define parallel branches through edges with source_handle: parallel-*:

[
  { "from": "parallel_start", "to": "branch_a", "source_handle": "parallel-0" },
  { "from": "parallel_start", "to": "branch_b", "source_handle": "parallel-1" }
]

Branches discovered from edges run concurrently and merge into a single dict keyed by branch node ID.

!!! note "Branch limit" A maximum of 20 parallel branches are allowed per node. This prevents resource exhaustion from malformed workflow definitions.

---

Combining Node Types

These node types compose naturally:

• Choice -> Parallel: Route to different parallel execution groups based on input
• Sub-workflow with Choice: A child workflow can contain its own choice routing
• LLM Router -> Sub-workflow: Classify intent, then run the appropriate sub-workflow
• Parallel -> Choice: Run branches in parallel, then route based on merged results

Diamond Convergence

Multiple branches can converge back to a single node:

Start -> Choice -> Branch A -> End
                -> Branch B -> End

Both branches connect to End, but only the taken branch executes. The end node sees results from whichever branch ran.

---

Related

• Iteration Nodes — For-each, filter, and reduce for array processing within workflows