diff --git a/lib/ex_ucan.ex b/lib/ex_ucan.ex
index 28a3c47..41e141e 100644
--- a/lib/ex_ucan.ex
+++ b/lib/ex_ucan.ex
@@ -2,17 +2,20 @@ defmodule ExUcan do
   @moduledoc """
   Documentation for `ExUcan`.
   """
+  alias ExUcan.Core.Token
+  alias ExUcan.Core.Structs.Ucan
 
-  @doc """
-  Hello world.
-
-  ## Examples
-
-      iex> ExUcan.hello()
-      :world
+  @spec build(struct(), map()) :: {:ok, Ucan.t()} | {:error, String.t()}
+  def build(keypair, _params) do
+    Token.build(%{
+      issuer: keypair,
+      audience: "did:key:z6MkwDK3M4PxU1FqcSt4quXghquH1MoWXGzTrNkNWTSy2NLD",
+      expiration: 86400
+    })
+  end
 
-  """
-  def hello do
-    :world
+  @spec encode(Ucan.t()) :: String.t()
+  def encode(ucan) do
+    Token.encode(ucan)
   end
 end
diff --git a/lib/ex_ucan/core/plugins.ex b/lib/ex_ucan/core/plugins.ex
index 108da09..bf56774 100644
--- a/lib/ex_ucan/core/plugins.ex
+++ b/lib/ex_ucan/core/plugins.ex
@@ -3,18 +3,18 @@ defmodule ExUcan.Core.Plugins do
 
   @spec verify_issuer_alg(String.t(), String.t()) :: boolean()
   def verify_issuer_alg(did, jwt_alg) do
-
   end
 
   @spec parseDidMethod(String.t()) :: String.t()
   defp parseDidMethod(did) do
     parts = String.split(did, ":")
+
     with {true, _} <- {Enum.at(parts, 0) == "did", 0},
-         {true, _} <- {String.length(Enum.at(parts, 1)) >=1, 1} do
-          {:ok, Enum.at(parts, 2)}
-         else
-          {false, 0} -> {:error, "Not a DID: #{did}"}
-          {false, 1} -> {:error, "No DID method included: #{did}"}
+         {true, _} <- {String.length(Enum.at(parts, 1)) >= 1, 1} do
+      {:ok, Enum.at(parts, 2)}
+    else
+      {false, 0} -> {:error, "Not a DID: #{did}"}
+      {false, 1} -> {:error, "No DID method included: #{did}"}
     end
   end
 end
diff --git a/lib/ex_ucan/core/structs.ex b/lib/ex_ucan/core/structs.ex
index 878848d..722ce08 100644
--- a/lib/ex_ucan/core/structs.ex
+++ b/lib/ex_ucan/core/structs.ex
@@ -1,3 +1,13 @@
+defmodule ExUcan.Core.Structs.Capability do
+  # TODO: All the docs needed
+  @type t :: %__MODULE__{
+          resource: String.t(),
+          ability: String.t(),
+          caveat: list(map())
+        }
+  defstruct [:resource, :ability, :caveat]
+end
+
 defmodule ExUcan.Core.Structs.UcanHeader do
   @moduledoc """
   Ucan header
@@ -9,17 +19,14 @@ defmodule ExUcan.Core.Structs.UcanHeader do
         }
 
   @derive Jason.Encoder
-  defstruct(
-    alg: "",
-    typ: ""
-  )
-
+  defstruct [:alg, :typ]
 end
 
 defmodule ExUcan.Core.Structs.UcanPayload do
   @moduledoc """
   Ucan Payload
   """
+  alias ExUcan.Core.Structs.Capability
 
   @type t :: %__MODULE__{
           ucv: String.t(),
@@ -29,22 +36,12 @@ defmodule ExUcan.Core.Structs.UcanPayload do
           exp: integer(),
           nnc: String.t(),
           fct: map(),
-          cap: map(),
+          cap: list(Capability.t()),
           prf: list(String.t())
         }
 
   @derive Jason.Encoder
-  defstruct(
-    ucv: "",
-    iss: "",
-    aud: "",
-    nbf: 0,
-    exp: nil,
-    nnc: "",
-    fct: %{},
-    cap: %{},
-    prf: []
-  )
+  defstruct [:ucv, :iss, :aud, :nbf, :exp, :nnc, :fct, :cap, :prf]
 end
 
 defmodule ExUcan.Core.Structs.Ucan do
@@ -62,10 +59,5 @@ defmodule ExUcan.Core.Structs.Ucan do
         }
 
   @derive Jason.Encoder
-  defstruct(
-    header: nil,
-    payload: nil,
-    signed_data: "",
-    signature: ""
-  )
+  defstruct [:header, :payload, :signed_data, :signature]
 end
diff --git a/lib/ex_ucan/core/token.ex b/lib/ex_ucan/core/token.ex
index f971270..d34ead0 100644
--- a/lib/ex_ucan/core/token.ex
+++ b/lib/ex_ucan/core/token.ex
@@ -11,19 +11,21 @@ defmodule ExUcan.Core.Token do
   @token_type "JWT"
   @version %{major: 0, minor: 10, patch: 0}
 
-  @spec build(params::%{
-    issuer: struct(),
-    audience: String.t(),
-    # Add capabilities struct later
-    capabilities: list(),
-    life_time_in_seconds: number(),
-    expiration: number(),
-    not_before: number(),
-    # Add Facts struct later
-    facts: list(),
-    proofs: list(String.t()),
-    add_nonce?: boolean()
-  }) :: Ucan.t()
+  @spec build(
+          params :: %{
+            issuer: struct(),
+            audience: String.t(),
+            # Add capabilities struct later
+            capabilities: list(),
+            life_time_in_seconds: number(),
+            expiration: number(),
+            not_before: number(),
+            # Add Facts struct later
+            facts: list(),
+            proofs: list(String.t()),
+            add_nonce?: boolean()
+          }
+        ) :: Ucan.t()
   def build(params) do
     {:ok, payload} = build_payload(%{params | issuer: Keymaterial.did(params.issuer)})
     sign_with_payload(payload, params.issuer)
@@ -74,12 +76,15 @@ defmodule ExUcan.Core.Token do
     "#{ucan.signed_data}.#{ucan.signature}"
   end
 
+  @spec validate(String.t()) :: {:ok, Ucan.t()} | {:error, String.t()}
+  def validate(encoded_ucan) do
+  end
+
   defp add_nonce(true), do: Utils.generate_nonce()
   defp add_nonce(false), do: nil
 
   @spec sign_with_payload(payload :: UcanPayload.t(), keypair :: struct()) :: Ucan.t()
   defp sign_with_payload(payload, keypair) do
-
     # TODO ExUcan.Core.Plugins.verify_issuer_alg
     header = %UcanHeader{alg: keypair.jwt_alg, typ: @token_type}
     encoded_header = encode_ucan_parts(header)
@@ -87,6 +92,7 @@ defmodule ExUcan.Core.Token do
 
     signed_data = "#{encoded_header}.#{encoded_payload}"
     signature = Keymaterial.sign(keypair, signed_data)
+
     %Ucan{
       header: header,
       payload: payload,
@@ -102,4 +108,34 @@ defmodule ExUcan.Core.Token do
     |> Base.url_encode64(padding: false)
   end
 
+  @spec is_expired?() :: boolean()
+  defp is_expired?() do
+  end
+
+  @spec parse_encoded_ucan(String.t()) ::
+          {:ok, {UcanHeader.t(), UcanPayload.t()}} | {:error, String.t()}
+  def parse_encoded_ucan(encoded_ucan) do
+    opts = [padding: false]
+
+    with {:ok, {header, payload, sign}} <- tear_into_parts(encoded_ucan),
+         {:ok, decoded_header} <- Base.url_decode64(header, opts) |> IO.inspect(),
+         {:ok, header} <- Jason.decode(decoded_header, keys: :atoms) |> IO.inspect(),
+         {:ok, decoded_payload} <- Base.url_decode64(payload, opts),
+         {:ok, payload} <- Jason.decode(decoded_payload, keys: :atoms) do
+      {:ok, struct(UcanHeader, header), struct(UcanPayload, payload)}
+    end
+  end
+
+  @spec tear_into_parts(String.t()) :: {:ok, tuple()} | {:error, String.t()}
+  defp tear_into_parts(encoded_ucan) do
+    err_msg =
+      "Can't parse UCAN: #{encoded_ucan}: Expected JWT format: 3 dot-separated base64url-encoded values."
+
+    case String.split(encoded_ucan, ".") |> List.to_tuple() do
+      {"", _, _} -> {:error, err_msg}
+      {_, "", _} -> {:error, err_msg}
+      {_, _, ""} -> {:error, err_msg}
+      ucan_parts -> {:ok, ucan_parts}
+    end
+  end
 end
diff --git a/lib/ex_ucan/plugins/ed25519/keypair.ex b/lib/ex_ucan/plugins/ed25519/keypair.ex
index 2af4062..ffd5165 100644
--- a/lib/ex_ucan/plugins/ed25519/keypair.ex
+++ b/lib/ex_ucan/plugins/ed25519/keypair.ex
@@ -4,7 +4,6 @@ defmodule ExUcan.Plugins.Ed25519.Keypair do
   """
   alias ExUcan.Core.Keymaterial
   alias ExUcan.Plugins.Ed25519.Crypto
-  @behaviour Keymaterial
   # TODO: more doc..
 
   # TODO: Need type doc
@@ -27,6 +26,7 @@ defmodule ExUcan.Plugins.Ed25519.Keypair do
 
   def create(exportable?) do
     {pub, priv} = :crypto.generate_key(:eddsa, :ed25519)
+
     %__MODULE__{
       jwt_alg: "EdDSA",
       secret_key: priv,
@@ -41,7 +41,12 @@ defmodule ExUcan.Plugins.Ed25519.Keypair do
     end
 
     def sign(keypair, payload) do
-      :public_key.sign(payload, :ignored, {:ed_pri, :ed25519, keypair.public_key, keypair.secret_key}, [])
+      :public_key.sign(
+        payload,
+        :ignored,
+        {:ed_pri, :ed25519, keypair.public_key, keypair.secret_key},
+        []
+      )
     end
   end
 end