How to assert response header postman

PostmanHow-ToBeginner · 3 min read

How to Assert Response Header in Postman Tests

In Postman, you can assert response headers using the pm.response.headers.get('Header-Name') method inside the Tests tab. Use pm.expect() to write assertions, for example, pm.expect(pm.response.headers.get('Content-Type')).to.equal('application/json') to verify a header value.

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Syntax

Use pm.response.headers.get('Header-Name') to get the value of a specific response header. Then use pm.expect() to assert its value.

pm.response.headers.get('Header-Name'): Retrieves the value of the header named 'Header-Name'.
pm.expect(value).to.equal(expectedValue): Checks if the actual header value matches the expected value.

javascript

pm.test('Check Content-Type header', () => {
    const contentType = pm.response.headers.get('Content-Type');
    pm.expect(contentType).to.equal('application/json');
});

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Example

This example shows how to assert that the Content-Type header is application/json and the Cache-Control header contains no-cache.

javascript

pm.test('Validate response headers', () => {
    const contentType = pm.response.headers.get('Content-Type');
    const cacheControl = pm.response.headers.get('Cache-Control');

    pm.expect(contentType).to.equal('application/json');
    pm.expect(cacheControl).to.include('no-cache');
});

Output

PASS Validate response headers

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Common Pitfalls

Common mistakes when asserting response headers in Postman include:

Using incorrect header names (header names are case-insensitive but must be exact strings).
Not checking if the header exists before asserting, which can cause errors if the header is missing.
Using pm.response.headers.get() incorrectly by passing an undefined or empty string.

Always verify the header name and consider adding a check for header presence.

javascript

pm.test('Check header exists before asserting', () => {
    const headerName = 'X-Custom-Header';
    const headerValue = pm.response.headers.get(headerName);
    pm.expect(headerValue, `${headerName} should be present`).to.not.be.undefined;
    pm.expect(headerValue).to.equal('expected-value');
});

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Quick Reference

Action	Code Snippet	Description
Get header value	pm.response.headers.get('Header-Name')	Retrieve the value of a response header
Assert header equals	pm.expect(value).to.equal('expected')	Check if header value matches exactly
Assert header contains	pm.expect(value).to.include('text')	Check if header value contains a substring
Check header exists	pm.expect(value).to.not.be.undefined	Verify header is present in response

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Key Takeaways

Use pm.response.headers.get('Header-Name') to access response headers in Postman tests.

Always assert header values with pm.expect() for clear pass/fail results.

Check if a header exists before asserting its value to avoid errors.

Header names are case-insensitive but must be spelled correctly in get().

Use .to.equal() for exact matches and .to.include() for partial matches.