diff --git a/README.md b/README.md
index e0ae7ae..c8f5651 100644
--- a/README.md
+++ b/README.md
@@ -19,9 +19,10 @@ Cacheability of response depends on how it was requested, so both request and re
 
 ```js
 const request = {
+    url: '/',
     method: 'GET',
     headers: {
-        'accept': '*/*',
+        accept: '*/*',
     },
 };
 
@@ -39,6 +40,12 @@ const options = {
 
 If `options.shared` is true (default), then response is evaluated from perspective of a shared cache (i.e. `private` is not cacheable and `s-maxage` is respected). If `options.shared` is false, then response is evaluated from perspective of a single-user cache (i.e. `private` is cacheable and `s-maxage` is ignored).
 
+### `satisfiesWithoutRevalidation(request)`
+
+If it returns `true`, then the given `request` matches the response this cache policy has been created with, and the existing response can be used without contacting the server.
+
+If it returns `false`, then the response may not be matching at all (e.g. it's different URL or method), or may require to be refreshed first.
+
 ### `storable()`
 
 Returns `true` if the response can be stored in a cache. If it's `false` then you MUST NOT store either request or the response.
diff --git a/index.js b/index.js
index c6c0830..6eb1c6c 100644
--- a/index.js
+++ b/index.js
@@ -88,21 +88,50 @@ CachePolicy.prototype = {
             this._res.headers.expires;
     },
 
+    satisfiesWithoutRevalidation(req) {
+        if (!req || !req.headers) {
+            throw Error("Request headers missing");
+        }
+
+        // When presented with a request, a cache MUST NOT reuse a stored response, unless:
+        // the presented request does not contain the no-cache pragma (Section 5.4), nor the no-cache cache directive,
+        // unless the stored response is successfully validated (Section 4.3), and
+        const requestCC = parseCacheControl(req.headers['cache-control']);
+        if (requestCC['no-cache'] || /no-cache/.test(req.headers.pragma)) {
+            return false;
+        }
+
+        // The presented effective request URI and that of the stored response match, and
+        return (!this._req.url || this._req.url === req.url) &&
+            // the request method associated with the stored response allows it to be used for the presented request, and
+            (!this._req.method || this._req.method === req.method) &&
+            // selecting header fields nominated by the stored response (if any) match those presented, and
+            this._varyMatches(req) &&
+            // the stored response is either:
+            // fresh, or allowed to be served stale
+            !this.stale() // TODO: allow stale
+    },
+
     _allowsStoringAuthenticated() {
         //  following Cache-Control response directives (Section 5.2.2) have such an effect: must-revalidate, public, and s-maxage.
         return this._rescc['must-revalidate'] || this._rescc['public'] || this._rescc['s-maxage'];
     },
 
-    _varyKeyForRequest(req) {
-        if (!this._res.headers.vary) return '';
+    _varyMatches(req) {
+        if (!this._res.headers.vary) {
+            return true;
+        }
+
+        // A Vary header field-value of "*" always fails to match
+        if (this._req.headers.vary === '*') {
+            return false;
+        }
 
-        let key = '';
         const fields = this._res.headers.vary.toLowerCase().split(/\s*,\s*/);
-        fields.sort();
         for(const name of fields) {
-            key += `${name}:${req.headers[name] || '÷'}\n`;
+            if (req.headers[name] !== this._req.headers[name]) return false;
         }
-        return key;
+        return true;
     },
 
     /**
diff --git a/test/varytest.js b/test/varytest.js
index 4396bc7..a23ac68 100644
--- a/test/varytest.js
+++ b/test/varytest.js
@@ -5,71 +5,63 @@ const CachePolicy = require('..');
 
 describe('Vary', function() {
     it('Basic', function() {
-        const cache1 = new CachePolicy({method:'GET',headers:{'weather': 'nice'}}, {headers:{'vary':'weather'}});
-        const cache2 = new CachePolicy({method:'GET',headers:{'weather': 'bad'}}, {headers:{'vary':'WEATHER'}});
+        const policy = new CachePolicy({headers:{'weather': 'nice'}}, {headers:{'cache-control':'max-age=5','vary':'weather'}});
 
-        assert.equal(cache1.cacheKey(), cache1.cacheKey());
-        assert.equal(cache2.cacheKey(), cache2.cacheKey());
-        assert.notEqual(cache1.cacheKey(), cache2.cacheKey());
+        assert(policy.satisfiesWithoutRevalidation({headers:{'weather': 'nice'}}));
+        assert(!policy.satisfiesWithoutRevalidation({headers:{'weather': 'bad'}}));
     });
 
-    it("* doesn't match other", function() {
-        const cache1 = new CachePolicy({method:'GET',headers:{'weather': 'ok'}}, {headers:{'vary':'*'}});
-        const cache2 = new CachePolicy({method:'GET',headers:{'weather': 'ok'}}, {headers:{'vary':'weather'}});
+    it("* doesn't match", function() {
+        const policy = new CachePolicy({headers:{'weather': 'ok'}}, {headers:{'cache-control':'max-age=5','vary':'*'}});
 
-        assert.equal(cache2.cacheKey(), cache2.cacheKey());
-        assert.notEqual(cache1.cacheKey(), cache2.cacheKey());
+        assert(!policy.satisfiesWithoutRevalidation({headers:{'weather': 'ok'}}));
     });
 
     it("* is stale", function() {
-        const cache1 = new CachePolicy({method:'GET',headers:{'weather': 'ok'}}, {headers:{'cache-control':'public,max-age=99', 'vary':'*'}});
-        const cache2 = new CachePolicy({method:'GET',headers:{'weather': 'ok'}}, {headers:{'cache-control':'public,max-age=99', 'vary':'weather'}});
+        const policy1 = new CachePolicy({headers:{'weather': 'ok'}}, {headers:{'cache-control':'public,max-age=99', 'vary':'*'}});
+        const policy2 = new CachePolicy({headers:{'weather': 'ok'}}, {headers:{'cache-control':'public,max-age=99', 'vary':'weather'}});
 
-        assert.notEqual(cache1.cacheKey(), cache2.cacheKey());
-
-        assert(cache1.stale());
-        assert(!cache2.stale());
+        assert(policy1.stale());
+        assert(!policy2.stale());
     });
 
     it('Values are case-sensitive', function() {
-        const cache1 = new CachePolicy({method:'GET',headers:{'weather': 'BAD'}}, {headers:{'vary':'weather'}});
-        const cache2 = new CachePolicy({method:'GET',headers:{'weather': 'bad'}}, {headers:{'vary':'weather'}});
+        const policy = new CachePolicy({headers:{'weather': 'BAD'}}, {headers:{'cache-control':'max-age=5','vary':'Weather'}});
 
-        assert.notEqual(cache1.cacheKey(), cache2.cacheKey());
+        assert(policy.satisfiesWithoutRevalidation({headers:{'weather': 'BAD'}}));
+        assert(!policy.satisfiesWithoutRevalidation({headers:{'weather': 'bad'}}));
     });
 
     it('Irrelevant headers ignored', function() {
-        const cache1 = new CachePolicy({method:'GET',headers:{'weather': 'nice'}}, {headers:{'vary':'moon-phase'}});
-        const cache2 = new CachePolicy({method:'GET',headers:{'weather': 'bad'}}, {headers:{'vary':'moon-phase'}});
+        const policy = new CachePolicy({headers:{'weather': 'nice'}}, {headers:{'cache-control':'max-age=5','vary':'moon-phase'}});
 
-        assert.equal(cache1.cacheKey(), cache1.cacheKey());
-        assert.equal(cache1.cacheKey(), cache2.cacheKey());
+        assert(policy.satisfiesWithoutRevalidation({headers:{'weather': 'bad'}}));
+        assert(policy.satisfiesWithoutRevalidation({headers:{'sun': 'shining'}}));
+        assert(!policy.satisfiesWithoutRevalidation({headers:{'moon-phase': 'full'}}));
     });
 
     it('Absence is meaningful', function() {
-        const cache1 = new CachePolicy({method:'GET',headers:{'weather': 'nice'}}, {headers:{'vary':'moon-phase'}});
-        const cache2 = new CachePolicy({method:'GET',headers:{'weather': 'bad'}}, {headers:{'vary':'sunshine'}});
+        const policy = new CachePolicy({headers:{'weather': 'nice'}}, {headers:{'cache-control':'max-age=5','vary':'moon-phase, weather'}});
 
-        assert.equal(cache2.cacheKey(), cache2.cacheKey());
-        assert.notEqual(cache1.cacheKey(), cache2.cacheKey());
+        assert(policy.satisfiesWithoutRevalidation({headers:{'weather': 'nice'}}));
+        assert(!policy.satisfiesWithoutRevalidation({headers:{'weather': 'nice', 'moon-phase': ''}}));
+        assert(!policy.satisfiesWithoutRevalidation({headers:{}}));
     });
 
     it('All values must match', function() {
-        const cache1 = new CachePolicy({method:'GET',headers:{'sun': 'shining', 'weather': 'nice'}}, {headers:{'vary':'weather, sun'}});
-        const cache2 = new CachePolicy({method:'GET',headers:{'sun': 'shining', 'weather': 'bad'}}, {headers:{'vary':'weather, sun'}});
-        assert.notEqual(cache1.cacheKey(), cache2.cacheKey());
+        const policy = new CachePolicy({headers:{'sun': 'shining', 'weather': 'nice'}}, {headers:{'cache-control':'max-age=5','vary':'weather, sun'}});
+
+        assert(policy.satisfiesWithoutRevalidation({headers:{'sun': 'shining', 'weather': 'nice'}}));
+        assert(!policy.satisfiesWithoutRevalidation({headers:{'sun': 'shining', 'weather': 'bad'}}));
     });
 
     it('Order is irrelevant', function() {
-        const cache1 = new CachePolicy({method:'GET',headers:{'weather': 'nice'}}, {headers:{'vary':'moon-phase, SUNSHINE'}});
-        const cache2 = new CachePolicy({method:'GET',headers:{'weather': 'bad'}}, {headers:{'vary':'sunshine, moon-phase'}});
-        assert.equal(cache1.cacheKey(), cache2.cacheKey());
-
-        const cache3 = new CachePolicy({method:'GET',headers:{'weather': 'nice'}}, {headers:{'vary':'moon-phase, weather'}});
-        const cache4 = new CachePolicy({method:'GET',headers:{'weather': 'nice'}}, {headers:{'vary':'weather, moon-phase'}});
-        assert.equal(cache3.cacheKey(), cache4.cacheKey());
+        const policy1 = new CachePolicy({headers:{'sun': 'shining', 'weather': 'nice'}}, {headers:{'cache-control':'max-age=5','vary':'weather, sun'}});
+        const policy2 = new CachePolicy({headers:{'sun': 'shining', 'weather': 'nice'}}, {headers:{'cache-control':'max-age=5','vary':'sun, weather'}});
 
-        assert.notEqual(cache1.cacheKey(), cache3.cacheKey());
-        assert.notEqual(cache2.cacheKey(), cache4.cacheKey());
+        assert(policy1.satisfiesWithoutRevalidation({headers:{'weather': 'nice', 'sun': 'shining'}}));
+        assert(policy1.satisfiesWithoutRevalidation({headers:{'sun': 'shining', 'weather': 'nice'}}));
+        assert(policy2.satisfiesWithoutRevalidation({headers:{'weather': 'nice', 'sun': 'shining'}}));
+        assert(policy2.satisfiesWithoutRevalidation({headers:{'sun': 'shining', 'weather': 'nice'}}));
     });
 });