diff --git a/jest.config.js b/jest.config.js
index 35556f3..efd3d7e 100644
--- a/jest.config.js
+++ b/jest.config.js
@@ -4,4 +4,9 @@ module.exports = {
   transform: {
     '^.+\\.(ts)$': 'ts-jest',
   },
+  globals: {
+    'ts-jest': {
+      isolatedModules: true,
+    },
+  },
 };
diff --git a/src/__tests__/checkParameters.spec.ts b/src/__tests__/checkParameters.spec.ts
new file mode 100644
index 0000000..2073e46
--- /dev/null
+++ b/src/__tests__/checkParameters.spec.ts
@@ -0,0 +1,107 @@
+import Client from '../internal';
+import { inputTypes, outputTypes, genomicModalities } from '../internal/internal.config';
+
+interface CheckParametersArguments {
+  inputType: string;
+  outputType: string;
+  // inputSet: string[];
+  genomicModality: string;
+  pValue?: number;
+}
+
+it('should not throw an error', () => {
+  const testObj: CheckParametersArguments = {
+    inputType: 'cell',
+    outputType: 'organ',
+    // inputSet: [],
+    genomicModality: 'fake',
+  };
+  expect(() => Client.checkParameters(testObj)).not.toThrow();
+});
+
+it('should throw an error when output type is not in output types', () => {
+  interface FakeCheckParametersArguments {
+    inputType: string;
+    outputType: string;
+    // inputSet: string[];
+    genomicModality: string;
+    pValue?: number;
+  }
+
+  const outputType: string = 'fake';
+  const testObj: FakeCheckParametersArguments = {
+    inputType: 'cell',
+    outputType,
+    // inputSet: [],
+    genomicModality: 'fake',
+  };
+  expect(() => Client.checkParameters(testObj)).toThrow(`${outputType} not in ${outputTypes}`);
+});
+
+it('should throw an error when input type does correspond to output type', () => {
+  const inputType: string = 'protein';
+  const outputType: string = 'organ';
+  const testObj: CheckParametersArguments = {
+    inputType,
+    outputType,
+    // inputSet: [],
+    genomicModality: 'fake',
+  };
+  expect(() => Client.checkParameters(testObj)).toThrow(`${inputType} not in ${inputTypes[outputType]}`);
+});
+
+it('should not throw an error when input type is gene and output type is cell', () => {
+  const testObj: CheckParametersArguments = {
+    inputType: 'gene',
+    outputType: 'cell',
+    // inputSet: [],
+    genomicModality: 'rna',
+  };
+  expect(() => Client.checkParameters(testObj)).not.toThrow();
+});
+
+it('should throw an error when input type is gene and output type is cell and genomic modality is not rna or atac', () => {
+  const genomicModality: string = 'fake';
+  const testObj: CheckParametersArguments = {
+    inputType: 'gene',
+    outputType: 'cell',
+    // inputSet: [],
+    genomicModality,
+  };
+  expect(() => Client.checkParameters(testObj)).toThrow(`${genomicModality} not in ${genomicModalities}`);
+});
+
+it('should not throw an error when input type is gene and output type is organ and p value within bounds', () => {
+  const testObj: CheckParametersArguments = {
+    inputType: 'gene',
+    outputType: 'cell',
+    // inputSet: [],
+    genomicModality: 'atac',
+    pValue: 0.2,
+  };
+  expect(() => Client.checkParameters(testObj)).not.toThrow();
+});
+
+it('should throw an error when input type is gene and output type is cell and p value is less than 0', () => {
+  const pValue: number = -0.1;
+  const testObj: CheckParametersArguments = {
+    inputType: 'gene',
+    outputType: 'organ',
+    // inputSet: [],
+    genomicModality: 'atac',
+    pValue,
+  };
+  expect(() => Client.checkParameters(testObj)).toThrow(`p_value ${pValue} should be in [0,1]`);
+});
+
+it('should throw an error when input type is cell and output type is gene and p value is greater than 0', () => {
+  const pValue: number = 1.2;
+  const testObj: CheckParametersArguments = {
+    inputType: 'organ',
+    outputType: 'gene',
+    // inputSet: [],
+    genomicModality: 'atac',
+    pValue,
+  };
+  expect(() => Client.checkParameters(testObj)).toThrow(`p_value ${pValue} should be in [0,1]`);
+});
diff --git a/src/__tests__/example.spec.ts b/src/__tests__/example.spec.ts
deleted file mode 100644
index 076d588..0000000
--- a/src/__tests__/example.spec.ts
+++ /dev/null
@@ -1,6 +0,0 @@
-import sum from '../example';
-
-test('Dummy unit test', () => {
-  const actual: number = sum(1, 2);
-  expect(actual).toBe(3);
-});
diff --git a/src/example.ts b/src/example.ts
deleted file mode 100644
index 3cc090d..0000000
--- a/src/example.ts
+++ /dev/null
@@ -1,5 +0,0 @@
-const sum = (a: number, b: number) => {
-  return a + b;
-};
-
-export default sum;
diff --git a/src/index.ts b/src/index.ts
index 5091123..655bdbb 100644
--- a/src/index.ts
+++ b/src/index.ts
@@ -1,2 +1,4 @@
-// eslint-disable-next-line
-export const greet = () => console.log('Hello, world!');
+import Client from './internal';
+
+// eslint-disable-next-line import/prefer-default-export
+export { Client };
diff --git a/src/internal/index.ts b/src/internal/index.ts
new file mode 100644
index 0000000..8bcccec
--- /dev/null
+++ b/src/internal/index.ts
@@ -0,0 +1,63 @@
+import { CheckParametersTypes } from './internal.types';
+import { outputTypes, inputTypes, genomicModalities } from './internal.config';
+
+class Client {
+  baseUrl: string;
+
+  constructor(baseUrl: string) {
+    // https://cells.dev.hubmapconsortium.org/api/'
+    this.baseUrl = baseUrl;
+  }
+
+  static checkParameters({
+    inputType,
+    outputType,
+    // inputSet,
+    genomicModality,
+    pValue = 0.05,
+  }: CheckParametersTypes): void {
+    if (!outputTypes.includes(outputType)) {
+      throw new Error(`${outputType} not in ${outputTypes}`);
+    }
+
+    if (!inputTypes[outputType].includes(inputType)) {
+      throw new Error(`${inputType} not in ${inputTypes[outputType]}`);
+    }
+
+    if (inputType === 'gene' && outputType === 'cell' && !genomicModalities.includes(genomicModality)) {
+      throw new Error(`${genomicModality} not in ${genomicModalities}`);
+    }
+
+    if (
+      (((inputType === 'organ' && outputType === 'gene') || (inputType === 'gene' && outputType === 'organ')) &&
+        pValue < 0) ||
+      pValue > 1
+    ) {
+      throw new Error(`p_value ${pValue} should be in [0,1]`);
+    }
+  }
+
+  /*
+  fillRequestObject() {}
+
+  hubmapQuery() {}
+
+  setIntersection() {}
+
+  setUnion() {}
+
+  setDifference() {}
+
+  operation() {}
+
+  checkDetailParameters() {}
+
+  setCount() {}
+
+  setListEvaluation() {}
+
+  setDetailEvaluation() {}
+  */
+}
+
+export default Client;
diff --git a/src/internal/internal.config.ts b/src/internal/internal.config.ts
new file mode 100644
index 0000000..0abd1a4
--- /dev/null
+++ b/src/internal/internal.config.ts
@@ -0,0 +1,15 @@
+import { InputTypes } from './internal.types';
+
+const outputTypes: string[] = ['cell', 'organ', 'gene', 'cluster'];
+
+const inputTypes: InputTypes = {
+  // Allowed input types vary depending on output type
+  cell: ['gene', 'organ', 'protein', 'dataset'],
+  organ: ['cell', 'gene'],
+  gene: ['organ', 'cluster'],
+  cluster: ['gene'],
+};
+
+const genomicModalities: string[] = ['rna', 'atac']; // Used for quantitative gene->cell queries
+
+export { outputTypes, inputTypes, genomicModalities };
diff --git a/src/internal/internal.types.ts b/src/internal/internal.types.ts
new file mode 100644
index 0000000..d072c14
--- /dev/null
+++ b/src/internal/internal.types.ts
@@ -0,0 +1,16 @@
+interface InputTypes {
+  cell: string[];
+  organ: string[];
+  gene: string[];
+  cluster: string[];
+}
+
+interface CheckParametersTypes {
+  inputType: string;
+  outputType: keyof InputTypes;
+  // inputSet: string[];
+  genomicModality: string;
+  pValue?: number;
+}
+
+export { InputTypes, CheckParametersTypes };