Merge pull request #13 from PolicyEngine/bot/issue-11

Improve MCP workflow for policy analysis

Author: nikhilwoodruff

src/policyengine_api/api/analysis.py

@@ -6,6 +6,13 @@
 
 This is an async operation - the endpoint returns immediately with a report_id,
 and you poll /analysis/economic-impact/{report_id} until status is "completed".
+
+WORKFLOW for full economic analysis:
+1. Create a policy with parameter changes: POST /policies
+2. Get a dataset: GET /datasets (look for UK/US datasets)
+3. Start analysis: POST /analysis/economic-impact with policy_id and dataset_id
+4. Check status: GET /analysis/economic-impact/{report_id} - repeat until status="completed"
+5. Review results: The completed response includes decile_impacts and program_statistics
 """
 
 import math

src/policyengine_api/api/datasets.py

@@ -23,6 +23,10 @@ def list_datasets(session: Session = Depends(get_session)):
 
     Returns datasets that can be used with the /analysis/economic-impact endpoint.
     Each dataset represents population microdata for a specific country and year.
+
+    USAGE: For UK analysis, look for datasets with names containing "uk" or "frs".
+    For US analysis, look for datasets with names containing "us" or "cps".
+    Use the dataset's id when calling /analysis/economic-impact.
     """
     datasets = session.exec(select(Dataset)).all()
     return datasets

src/policyengine_api/api/parameters.py

@@ -21,15 +21,31 @@
 @router.get("/", response_model=List[ParameterRead])
 @cache(expire=3600)  # Cache for 1 hour
 def list_parameters(
-    skip: int = 0, limit: int = 100, session: Session = Depends(get_session)
+    skip: int = 0,
+    limit: int = 100,
+    search: str | None = None,
+    session: Session = Depends(get_session),
 ):
-    """List available parameters with pagination.
+    """List available parameters with pagination and search.
 
     Parameters are policy levers (e.g. tax rates, thresholds, benefit amounts)
     that can be modified in reforms. Use parameter names when creating policies.
+
+    Use the `search` parameter to filter by parameter name, label, or description.
+    For example: search="basic_rate" or search="income tax"
     """
+    query = select(Parameter)
+
+    if search:
+        search_filter = (
+            Parameter.name.contains(search)
+            | Parameter.label.contains(search)
+            | Parameter.description.contains(search)
+        )
+        query = query.where(search_filter)
+
     parameters = session.exec(
-        select(Parameter).order_by(Parameter.name).offset(skip).limit(limit)
+        query.order_by(Parameter.name).offset(skip).limit(limit)
     ).all()
     return parameters
 

src/policyengine_api/api/policies.py

@@ -3,29 +3,109 @@
 Policies represent tax-benefit parameter reforms that can be compared against
 baseline (current law). Create a policy, then use its ID with the household
 calculation or economic impact endpoints to see the reform's effects.
+
+WORKFLOW: To analyze a policy reform (e.g. lowering UK basic income tax rate to 16%):
+
+1. Search for the parameter: GET /parameters?search=basic_rate
+2. Note the parameter_id from the results
+3. Create a policy with parameter values:
+   POST /policies
+   {
+     "name": "Lower basic rate to 16p",
+     "description": "Reduce UK basic income tax rate from 20p to 16p",
+     "parameter_values": [
+       {
+         "parameter_id": "<uuid-from-step-1>",
+         "value_json": 0.16,
+         "start_date": "2026-01-01T00:00:00Z",
+         "end_date": null
+       }
+     ]
+   }
+4. Test on a household: POST /household/impact with the policy_id
+5. Run population analysis: POST /analysis/economic-impact with policy_id and dataset_id
+6. Poll GET /analysis/economic-impact/{report_id} until status="completed"
 """
 
+from datetime import datetime
 from typing import List
 from uuid import UUID
 
 from fastapi import APIRouter, Depends, HTTPException
 from sqlmodel import Session, select
 
-from policyengine_api.models import Policy, PolicyCreate, PolicyRead
+from policyengine_api.models import (
+    Parameter,
+    ParameterValue,
+    Policy,
+    PolicyCreate,
+    PolicyRead,
+)
 from policyengine_api.services.database import get_session
 
 router = APIRouter(prefix="/policies", tags=["policies"])
 
 
 @router.post("/", response_model=PolicyRead)
 def create_policy(policy: PolicyCreate, session: Session = Depends(get_session)):
-    """Create a new policy reform.
+    """Create a new policy reform with parameter values.
 
     Policies define changes to tax-benefit parameters. After creating a policy,
     use its ID with /household/calculate or /analysis/economic-impact to see effects.
+
+    Include parameter_values in the request to specify which parameters to change:
+    {
+        "name": "Lower basic rate to 16p",
+        "description": "Reduce UK basic income tax rate from 20p to 16p",
+        "parameter_values": [
+            {
+                "parameter_id": "uuid-from-parameters-search",
+                "value_json": 0.16,
+                "start_date": "2026-01-01T00:00:00Z",
+                "end_date": null
+            }
+        ]
+    }
     """
-    db_policy = Policy.model_validate(policy)
+    # Create the policy
+    db_policy = Policy(name=policy.name, description=policy.description)
     session.add(db_policy)
+    session.flush()  # Get the policy ID before adding parameter values
+
+    # Create associated parameter values
+    for pv_data in policy.parameter_values:
+        # Validate parameter exists
+        param = session.get(Parameter, pv_data["parameter_id"])
+        if not param:
+            raise HTTPException(
+                status_code=404,
+                detail=f"Parameter {pv_data['parameter_id']} not found",
+            )
+
+        # Parse dates
+        start_date = (
+            datetime.fromisoformat(pv_data["start_date"].replace("Z", "+00:00"))
+            if isinstance(pv_data["start_date"], str)
+            else pv_data["start_date"]
+        )
+        end_date = None
+        if pv_data.get("end_date"):
+            end_date = (
+                datetime.fromisoformat(pv_data["end_date"].replace("Z", "+00:00"))
+                if isinstance(pv_data["end_date"], str)
+                else pv_data["end_date"]
+            )
+
+        # Create parameter value
+        db_pv = ParameterValue(
+            parameter_id=pv_data["parameter_id"],
+            value_json=pv_data["value_json"],
+            start_date=start_date,
+            end_date=end_date,
+            policy_id=db_policy.id,
+        )
+        session.add(db_pv)
+
     session.commit()
     session.refresh(db_policy)
     return db_policy

src/policyengine_api/models/policy.py

@@ -29,9 +29,29 @@ class Policy(PolicyBase, table=True):
 
 
 class PolicyCreate(PolicyBase):
-    """Schema for creating policies."""
-
-    pass
+    """Schema for creating policies.
+
+    When creating a policy with parameter values, provide a list of
+    parameter value definitions. Each parameter value needs:
+    - parameter_id: UUID of the parameter to modify
+    - value_json: The new value (number, string, or nested object)
+    - start_date: When this value takes effect
+    - end_date: Optional end date (null for indefinite)
+
+    Example:
+    {
+        "name": "Lower basic rate to 16p",
+        "description": "Reduce UK basic income tax rate",
+        "parameter_values": [{
+            "parameter_id": "uuid-here",
+            "value_json": 0.16,
+            "start_date": "2026-01-01T00:00:00Z",
+            "end_date": null
+        }]
+    }
+    """
+
+    parameter_values: list[dict] = []
 
 
 class PolicyRead(PolicyBase):