diff --git a/CHANGELOG.md b/CHANGELOG.md
index 8d7d430..f019be1 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -64,6 +64,8 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 - Add an explicit research-compatibility rule requiring parser, emitter,
   validation, and typed conversion work to start from PureYAMLResearch behavior
   without copying implementation code.
+- Add a fixture-backed scalar and explicit-tag compatibility corpus with exact
+  success, string-preservation, unsupported-spelling, and invalid-tag errors.
 
 ### Changed
 
@@ -76,3 +78,5 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
   written in a different order than they were requested.
 - Make keyed default `superEncoder()` and `superDecoder()` use the standard
   `super` mapping key instead of the current mapping.
+- Resolve Yams-compatible plain scalar spellings for `yes`/`no` booleans,
+  radix-prefixed integers, numeric separators, and `.inf`/`.nan` floats.
diff --git a/README.md b/README.md
index dbd2739..c3b6024 100644
--- a/README.md
+++ b/README.md
@@ -63,6 +63,27 @@ flowchart TB
 
 #10 Typed Decoding and Encoding is complete in main.
 
+#11 YAML Compatibility Corpus is active:
+
+```mermaid
+flowchart TB
+  classDef done fill:#ddf9e4,stroke:#34c759,color:#111827
+  classDef review fill:#fff7d6,stroke:#ffcc00,color:#111827
+  classDef epic fill:#f2e5ff,stroke:#af52de,color:#111827
+  classDef todo fill:#f2f4f7,stroke:#8e8e93,color:#111827
+  Epic11["#11 YAML Compatibility Corpus"]:::epic
+  Scalar24["#24 Scalar and Tag Corpus"]:::done
+  Collection25["#25 Collection and Anchor Corpus"]:::todo
+  Gaps27["#27 Unsupported YAML Gaps"]:::todo
+  Literal19["#19 Literal Block Emission"]:::todo
+  Downstream26["#26 Downstream Document Fixtures"]:::todo
+  Epic11 --> Scalar24
+  Scalar24 --> Collection25
+  Collection25 --> Gaps27
+  Gaps27 --> Literal19
+  Literal19 --> Downstream26
+```
+
 ## Status
 
 This repository starts with the first real parser milestone: block mappings,
diff --git a/Sources/Parsing/EventComposer.swift b/Sources/Parsing/EventComposer.swift
index eab4cf2..1940374 100644
--- a/Sources/Parsing/EventComposer.swift
+++ b/Sources/Parsing/EventComposer.swift
@@ -163,12 +163,12 @@ extension PureYAML.Parsing.EventComposer {
         case "tag:yaml.org,2002:str":
             return .string(value)
         case "tag:yaml.org,2002:int":
-            guard let int = Int(scalarParser.trim(value)) else {
+            guard let int = scalarParser.parseInteger(scalarParser.trim(value)) else {
                 throw invalidTaggedScalar(tag: "tag:yaml.org,2002:int", value: value, mark: mark)
             }
             return .int(int)
         case "tag:yaml.org,2002:float":
-            guard let double = Double(scalarParser.trim(value)) else {
+            guard let double = scalarParser.parseDouble(scalarParser.trim(value)) else {
                 throw invalidTaggedScalar(tag: "tag:yaml.org,2002:float", value: value, mark: mark)
             }
             return .double(double)
@@ -185,14 +185,10 @@ extension PureYAML.Parsing.EventComposer {
         _ value: String,
         mark: PureYAML.Parsing.Mark,
     ) throws -> PureYAML.Model.Value {
-        switch scalarParser.trim(value) {
-        case "true", "True", "TRUE":
-            return .bool(true)
-        case "false", "False", "FALSE":
-            return .bool(false)
-        default:
+        guard let bool = scalarParser.parseBool(scalarParser.trim(value)) else {
             throw invalidTaggedScalar(tag: "tag:yaml.org,2002:bool", value: value, mark: mark)
         }
+        return .bool(bool)
     }
 
     func normalizedScalarTag(_ tag: String?) -> String? {
diff --git a/Sources/Parsing/Scalar.swift b/Sources/Parsing/Scalar.swift
index 9ced40e..74aa966 100644
--- a/Sources/Parsing/Scalar.swift
+++ b/Sources/Parsing/Scalar.swift
@@ -17,31 +17,92 @@ extension PureYAML.Parsing.Parser {
         switch value {
         case "", "~", "null", "Null", "NULL":
             return .null
-        case "true", "True", "TRUE":
-            return .bool(true)
-        case "false", "False", "FALSE":
-            return .bool(false)
         default:
             break
         }
 
+        if let bool = parseBool(value) {
+            return .bool(bool)
+        }
         if value.hasPrefix("\"") {
             return try .string(parseDoubleQuoted(value, line: line))
         }
         if value.hasPrefix("'") {
             return try .string(parseSingleQuoted(value, line: line))
         }
-        if let int = Int(value), !value.contains(".") {
+        if let int = parseInteger(value), !value.contains(".") {
             return .int(int)
         }
         if value.contains(".") || value.contains("e") || value.contains("E") {
-            if let double = Double(value) {
+            if let double = parseDouble(value) {
                 return .double(double)
             }
         }
         return .string(value)
     }
 
+    func parseBool(_ text: String) -> Bool? {
+        switch text {
+        case "true", "True", "TRUE", "yes", "Yes", "YES", "on", "On", "ON":
+            true
+        case "false", "False", "FALSE", "no", "No", "NO", "off", "Off", "OFF":
+            false
+        default:
+            nil
+        }
+    }
+
+    func parseInteger(_ text: String) -> Int? {
+        let value = removingNumericSeparators(from: text)
+        let negative = value.hasPrefix("-")
+        let hasSign = negative || value.hasPrefix("+")
+        let unsigned = hasSign ? String(value.dropFirst()) : value
+
+        guard !unsigned.isEmpty else {
+            return nil
+        }
+        guard unsigned != "0" else {
+            return 0
+        }
+
+        let radixPrefixes: [(prefix: String, radix: Int)] = [
+            ("0x", 16),
+            ("0X", 16),
+            ("0b", 2),
+            ("0B", 2),
+            ("0o", 8),
+            ("0O", 8),
+            ("0", 8),
+        ]
+
+        for radixPrefix in radixPrefixes where unsigned.hasPrefix(radixPrefix.prefix) {
+            let digits = String(unsigned.dropFirst(radixPrefix.prefix.count))
+            guard !digits.isEmpty, let magnitude = Int(digits, radix: radixPrefix.radix) else {
+                return nil
+            }
+            return negative ? -magnitude : magnitude
+        }
+
+        return Int(value)
+    }
+
+    func parseDouble(_ text: String) -> Double? {
+        switch text {
+        case ".inf", ".Inf", ".INF", "+.inf", "+.Inf", "+.INF":
+            .infinity
+        case "-.inf", "-.Inf", "-.INF":
+            -.infinity
+        case ".nan", ".NaN", ".NAN", "+.nan", "+.NaN", "+.NAN", "-.nan", "-.NaN", "-.NAN":
+            .nan
+        default:
+            Double(removingNumericSeparators(from: text))
+        }
+    }
+
+    func removingNumericSeparators(from text: String) -> String {
+        text.filter { $0 != "_" }
+    }
+
     func parseSingleQuoted(
         _ text: String,
         line: Int,
diff --git a/Tests/ParsingCompatibilityTests.swift b/Tests/ParsingCompatibilityTests.swift
index 9bf686a..9a82d28 100644
--- a/Tests/ParsingCompatibilityTests.swift
+++ b/Tests/ParsingCompatibilityTests.swift
@@ -3,6 +3,67 @@ import Testing
 
 @Suite("Parsing Compatibility")
 struct ParsingCompatibilityTests {
+    @Test(
+        "Resolves selected Yams-compatible scalar spellings",
+        arguments: ScalarCompatibilityFixtures.resolvedScalars,
+    )
+    func test_selectedScalarResolution(testCase: ScalarCompatibilityFixtures.SuccessCase) throws {
+        let root = try requireMapping(PureYAML.parse(testCase.yaml))
+
+        expectScalar(root?["value"], testCase.expected)
+        #expect(root?["missing"] == nil)
+        if let forbiddenString = testCase.forbiddenString {
+            #expect(root?["value"] != .string(forbiddenString))
+        }
+    }
+
+    @Test(
+        "Applies explicit built-in scalar tags",
+        arguments: ScalarCompatibilityFixtures.explicitScalarTags,
+    )
+    func test_explicitBuiltInScalarTags(testCase: ScalarCompatibilityFixtures.SuccessCase) throws {
+        let root = try requireMapping(PureYAML.parse(testCase.yaml))
+
+        expectScalar(root?["value"], testCase.expected)
+        #expect(root?["missing"] == nil)
+        if let forbiddenString = testCase.forbiddenString {
+            #expect(root?["value"] != .string(forbiddenString))
+        }
+    }
+
+    @Test(
+        "Keeps explicit and quoted strings from resolving",
+        arguments: ScalarCompatibilityFixtures.stringScalars,
+    )
+    func test_stringScalarsDoNotResolve(testCase: ScalarCompatibilityFixtures.SuccessCase) throws {
+        let root = try requireMapping(PureYAML.parse(testCase.yaml))
+
+        expectScalar(root?["value"], testCase.expected)
+        #expect(root?["value"] != .bool(true))
+        #expect(root?["value"] != .bool(false))
+        #expect(root?["missing"] == nil)
+    }
+
+    @Test(
+        "Pins unsupported scalar spellings as strings",
+        arguments: ScalarCompatibilityFixtures.unsupportedScalars,
+    )
+    func test_unsupportedScalarSpellingsStayStrings(testCase: ScalarCompatibilityFixtures.SuccessCase) throws {
+        let root = try requireMapping(PureYAML.parse(testCase.yaml))
+
+        expectScalar(root?["value"], testCase.expected)
+        #expect(root?["value"] != .null)
+        #expect(root?["missing"] == nil)
+    }
+
+    @Test(
+        "Reports exact invalid explicit scalar tag errors",
+        arguments: ScalarCompatibilityFixtures.invalidExplicitScalarTags,
+    )
+    func test_invalidExplicitScalarTags(testCase: ScalarCompatibilityFixtures.ErrorCase) {
+        expectParseError(testCase.yaml, testCase.expected)
+    }
+
     @Test("Parses directives document markers and explicit scalar tags")
     func test_directivesDocumentMarkersAndExplicitScalarTags() throws {
         let root = try requireMapping(PureYAML.parse(
@@ -27,4 +88,32 @@ struct ParsingCompatibilityTests {
         #expect(root?["missing"] == .null)
         #expect(root?["custom"] == .bool(true))
     }
+
+    private func expectScalar(
+        _ value: PureYAML.Model.Value?,
+        _ expected: ScalarCompatibilityFixtures.Expected,
+    ) {
+        switch expected {
+        case .null:
+            #expect(value == .null)
+        case let .bool(expected):
+            #expect(value == .bool(expected))
+        case let .int(expected):
+            #expect(value == .int(expected))
+        case let .double(expected):
+            guard case let .double(actual)? = value else {
+                recordIssue("expected double \(expected), got \(String(describing: value))")
+                return
+            }
+            #expect(actual == expected)
+        case .nan:
+            guard case let .double(actual)? = value else {
+                recordIssue("expected NaN double, got \(String(describing: value))")
+                return
+            }
+            #expect(actual.isNaN)
+        case let .string(expected):
+            #expect(value == .string(expected))
+        }
+    }
 }
diff --git a/Tests/ScalarCompatibilityFixtures.swift b/Tests/ScalarCompatibilityFixtures.swift
new file mode 100644
index 0000000..86f57c2
--- /dev/null
+++ b/Tests/ScalarCompatibilityFixtures.swift
@@ -0,0 +1,151 @@
+@testable import PureYAML
+
+enum ScalarCompatibilityFixtures {
+    enum Expected {
+        case null
+        case bool(Bool)
+        case int(Int)
+        case double(Double)
+        case nan
+        case string(String)
+    }
+
+    struct SuccessCase {
+        var yaml: String
+        var expected: Expected
+        var forbiddenString: String?
+
+        init(
+            _ yaml: String,
+            _ expected: Expected,
+            forbiddenString: String? = nil,
+        ) {
+            self.yaml = yaml
+            self.expected = expected
+            self.forbiddenString = forbiddenString
+        }
+    }
+
+    struct ErrorCase {
+        var yaml: String
+        var expected: PureYAML.Parsing.ParseError
+    }
+
+    static let resolvedScalars: [SuccessCase] = [
+        SuccessCase("value:", .null),
+        SuccessCase("value: ~", .null, forbiddenString: "~"),
+        SuccessCase("value: null", .null, forbiddenString: "null"),
+        SuccessCase("value: Null", .null, forbiddenString: "Null"),
+        SuccessCase("value: NULL", .null, forbiddenString: "NULL"),
+        SuccessCase("value: true", .bool(true), forbiddenString: "true"),
+        SuccessCase("value: True", .bool(true), forbiddenString: "True"),
+        SuccessCase("value: TRUE", .bool(true), forbiddenString: "TRUE"),
+        SuccessCase("value: yes", .bool(true), forbiddenString: "yes"),
+        SuccessCase("value: Yes", .bool(true), forbiddenString: "Yes"),
+        SuccessCase("value: YES", .bool(true), forbiddenString: "YES"),
+        SuccessCase("value: on", .bool(true), forbiddenString: "on"),
+        SuccessCase("value: On", .bool(true), forbiddenString: "On"),
+        SuccessCase("value: ON", .bool(true), forbiddenString: "ON"),
+        SuccessCase("value: false", .bool(false), forbiddenString: "false"),
+        SuccessCase("value: False", .bool(false), forbiddenString: "False"),
+        SuccessCase("value: FALSE", .bool(false), forbiddenString: "FALSE"),
+        SuccessCase("value: no", .bool(false), forbiddenString: "no"),
+        SuccessCase("value: No", .bool(false), forbiddenString: "No"),
+        SuccessCase("value: NO", .bool(false), forbiddenString: "NO"),
+        SuccessCase("value: off", .bool(false), forbiddenString: "off"),
+        SuccessCase("value: Off", .bool(false), forbiddenString: "Off"),
+        SuccessCase("value: OFF", .bool(false), forbiddenString: "OFF"),
+        SuccessCase("value: 12345", .int(12345), forbiddenString: "12345"),
+        SuccessCase("value: +12345", .int(12345), forbiddenString: "+12345"),
+        SuccessCase("value: -7", .int(-7), forbiddenString: "-7"),
+        SuccessCase("value: 0o14", .int(12), forbiddenString: "0o14"),
+        SuccessCase("value: 014", .int(12), forbiddenString: "014"),
+        SuccessCase("value: 0xC", .int(12), forbiddenString: "0xC"),
+        SuccessCase("value: 0b1010", .int(10), forbiddenString: "0b1010"),
+        SuccessCase("value: 1_000", .int(1000), forbiddenString: "1_000"),
+        SuccessCase("value: 1.23015e+3", .double(1230.15), forbiddenString: "1.23015e+3"),
+        SuccessCase("value: 12.3015e+02", .double(1230.15), forbiddenString: "12.3015e+02"),
+        SuccessCase("value: 1230.15", .double(1230.15), forbiddenString: "1230.15"),
+        SuccessCase("value: 1_000.25", .double(1000.25), forbiddenString: "1_000.25"),
+        SuccessCase("value: -.inf", .double(-.infinity), forbiddenString: "-.inf"),
+        SuccessCase("value: +.INF", .double(.infinity), forbiddenString: "+.INF"),
+        SuccessCase("value: .NaN", .nan, forbiddenString: ".NaN"),
+    ]
+
+    static let explicitScalarTags: [SuccessCase] = [
+        SuccessCase("value: !!str true", .string("true")),
+        SuccessCase("value: !<tag:yaml.org,2002:str> 0xC", .string("0xC")),
+        SuccessCase("value: !!int 0xC", .int(12), forbiddenString: "0xC"),
+        SuccessCase("value: !!int \"1_000\"", .int(1000), forbiddenString: "1_000"),
+        SuccessCase("value: !<tag:yaml.org,2002:int> 0b1010", .int(10), forbiddenString: "0b1010"),
+        SuccessCase("value: !!float .NaN", .nan, forbiddenString: ".NaN"),
+        SuccessCase("value: !!float \"-.inf\"", .double(-.infinity), forbiddenString: "-.inf"),
+        SuccessCase("value: !!bool YES", .bool(true), forbiddenString: "YES"),
+        SuccessCase("value: !!bool \"off\"", .bool(false), forbiddenString: "off"),
+        SuccessCase("value: !!null ignored", .null, forbiddenString: "ignored"),
+        SuccessCase(
+            """
+            %YAML 1.2
+            %TAG !yaml! tag:yaml.org,2002:
+            ---
+            value: !yaml!bool On
+            """,
+            .bool(true),
+            forbiddenString: "On",
+        ),
+    ]
+
+    static let stringScalars: [SuccessCase] = [
+        SuccessCase("value: \"true\"", .string("true")),
+        SuccessCase("value: 'false'", .string("false")),
+        SuccessCase("value: \"0xC\"", .string("0xC")),
+        SuccessCase("value: '1_000'", .string("1_000")),
+        SuccessCase("value: !!str yes", .string("yes")),
+        SuccessCase("value: !<tag:yaml.org,2002:str> .nan", .string(".nan")),
+    ]
+
+    static let unsupportedScalars: [SuccessCase] = [
+        SuccessCase("value: 1:20", .string("1:20")),
+        SuccessCase("value: 2002-04-28", .string("2002-04-28")),
+        SuccessCase("value: 09", .string("09")),
+    ]
+
+    static let invalidExplicitScalarTags: [ErrorCase] = [
+        ErrorCase(
+            yaml: "value: !!int nope",
+            expected: .invalidTaggedScalar(
+                tag: "tag:yaml.org,2002:int",
+                value: "nope",
+                line: 1,
+                column: 8,
+            ),
+        ),
+        ErrorCase(
+            yaml: "value: !!int 0xG",
+            expected: .invalidTaggedScalar(
+                tag: "tag:yaml.org,2002:int",
+                value: "0xG",
+                line: 1,
+                column: 8,
+            ),
+        ),
+        ErrorCase(
+            yaml: "value: !!float nope",
+            expected: .invalidTaggedScalar(
+                tag: "tag:yaml.org,2002:float",
+                value: "nope",
+                line: 1,
+                column: 8,
+            ),
+        ),
+        ErrorCase(
+            yaml: "value: !!bool maybe",
+            expected: .invalidTaggedScalar(
+                tag: "tag:yaml.org,2002:bool",
+                value: "maybe",
+                line: 1,
+                column: 8,
+            ),
+        ),
+    ]
+}