diff --git a/Cargo.lock b/Cargo.lock
index 9fd8dfb..71896d5 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -58,6 +58,44 @@ version = "1.0.102"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "7f202df86484c868dbad7eaa557ef785d5c66295e41b460ef922eca0723b842c"
 
+[[package]]
+name = "assert_cmd"
+version = "2.2.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "9a686bbee5efb88a82df0621b236e74d925f470e5445d3220a5648b892ec99c9"
+dependencies = [
+ "anstyle",
+ "bstr",
+ "libc",
+ "predicates",
+ "predicates-core",
+ "predicates-tree",
+ "wait-timeout",
+]
+
+[[package]]
+name = "bitflags"
+version = "2.11.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "843867be96c8daad0d758b57df9392b6d8d271134fce549de6ce169ff98a92af"
+
+[[package]]
+name = "bstr"
+version = "1.12.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "63044e1ae8e69f3b5a92c736ca6269b8d12fa7efe39bf34ddb06d102cf0e2cab"
+dependencies = [
+ "memchr",
+ "regex-automata",
+ "serde",
+]
+
+[[package]]
+name = "cfg-if"
+version = "1.0.4"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "9330f8b2ff13f34540b44e946ef35111825727b38d33286ef986142615121801"
+
 [[package]]
 name = "clap"
 version = "4.6.0"
@@ -104,23 +142,105 @@ version = "1.0.5"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "1d07550c9036bf2ae0c684c4297d503f838287c83c53686d05370d0e139ae570"
 
+[[package]]
+name = "difflib"
+version = "0.4.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "6184e33543162437515c2e2b48714794e37845ec9851711914eec9d308f6ebe8"
+
+[[package]]
+name = "equivalent"
+version = "1.0.2"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "877a4ace8713b0bcf2a4e7eec82529c029f1d0619886d18145fea96c3ffe5c0f"
+
+[[package]]
+name = "errno"
+version = "0.3.14"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "39cab71617ae0d63f51a36d69f866391735b51691dbda63cf6f96d042b63efeb"
+dependencies = [
+ "libc",
+ "windows-sys",
+]
+
+[[package]]
+name = "fastrand"
+version = "2.4.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "9f1f227452a390804cdb637b74a86990f2a7d7ba4b7d5693aac9b4dd6defd8d6"
+
+[[package]]
+name = "foldhash"
+version = "0.1.5"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "d9c4f5dac5e15c24eb999c26181a6ca40b39fe946cbe4c263c7209467bc83af2"
+
+[[package]]
+name = "getrandom"
+version = "0.4.2"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "0de51e6874e94e7bf76d726fc5d13ba782deca734ff60d5bb2fb2607c7406555"
+dependencies = [
+ "cfg-if",
+ "libc",
+ "r-efi",
+ "wasip2",
+ "wasip3",
+]
+
 [[package]]
 name = "gitea-pr-review"
 version = "0.1.0"
 dependencies = [
  "anyhow",
+ "assert_cmd",
  "clap",
  "serde",
  "serde_json",
+ "tempfile",
  "thiserror",
 ]
 
+[[package]]
+name = "hashbrown"
+version = "0.15.5"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "9229cfe53dfd69f0609a49f65461bd93001ea1ef889cd5529dd176593f5338a1"
+dependencies = [
+ "foldhash",
+]
+
+[[package]]
+name = "hashbrown"
+version = "0.16.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "841d1cc9bed7f9236f321df977030373f4a4163ae1a7dbfe1a51a2c1a51d9100"
+
 [[package]]
 name = "heck"
 version = "0.5.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "2304e00983f87ffb38b55b444b5e3b60a884b5d30c0fca7d82fe33449bbe55ea"
 
+[[package]]
+name = "id-arena"
+version = "2.3.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "3d3067d79b975e8844ca9eb072e16b31c3c1c36928edf9c6789548c524d0d954"
+
+[[package]]
+name = "indexmap"
+version = "2.13.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "45a8a2b9cb3e0b0c1803dbb0758ffac5de2f425b23c28f518faabd9d805342ff"
+dependencies = [
+ "equivalent",
+ "hashbrown 0.16.1",
+ "serde",
+ "serde_core",
+]
+
 [[package]]
 name = "is_terminal_polyfill"
 version = "1.70.2"
@@ -133,18 +253,85 @@ version = "1.0.18"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "8f42a60cbdf9a97f5d2305f08a87dc4e09308d1276d28c869c684d7777685682"
 
+[[package]]
+name = "leb128fmt"
+version = "0.1.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "09edd9e8b54e49e587e4f6295a7d29c3ea94d469cb40ab8ca70b288248a81db2"
+
+[[package]]
+name = "libc"
+version = "0.2.184"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "48f5d2a454e16a5ea0f4ced81bd44e4cfc7bd3a507b61887c99fd3538b28e4af"
+
+[[package]]
+name = "linux-raw-sys"
+version = "0.12.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "32a66949e030da00e8c7d4434b251670a91556f4144941d37452769c25d58a53"
+
+[[package]]
+name = "log"
+version = "0.4.29"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "5e5032e24019045c762d3c0f28f5b6b8bbf38563a65908389bf7978758920897"
+
 [[package]]
 name = "memchr"
 version = "2.8.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "f8ca58f447f06ed17d5fc4043ce1b10dd205e060fb3ce5b979b8ed8e59ff3f79"
 
+[[package]]
+name = "once_cell"
+version = "1.21.4"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "9f7c3e4beb33f85d45ae3e3a1792185706c8e16d043238c593331cc7cd313b50"
+
 [[package]]
 name = "once_cell_polyfill"
 version = "1.70.2"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "384b8ab6d37215f3c5301a95a4accb5d64aa607f1fcb26a11b5303878451b4fe"
 
+[[package]]
+name = "predicates"
+version = "3.1.4"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "ada8f2932f28a27ee7b70dd6c1c39ea0675c55a36879ab92f3a715eaa1e63cfe"
+dependencies = [
+ "anstyle",
+ "difflib",
+ "predicates-core",
+]
+
+[[package]]
+name = "predicates-core"
+version = "1.0.10"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "cad38746f3166b4031b1a0d39ad9f954dd291e7854fcc0eed52ee41a0b50d144"
+
+[[package]]
+name = "predicates-tree"
+version = "1.0.13"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "d0de1b847b39c8131db0467e9df1ff60e6d0562ab8e9a16e568ad0fdb372e2f2"
+dependencies = [
+ "predicates-core",
+ "termtree",
+]
+
+[[package]]
+name = "prettyplease"
+version = "0.2.37"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "479ca8adacdd7ce8f1fb39ce9ecccbfe93a3f1344b3d0d97f20bc0196208f62b"
+dependencies = [
+ "proc-macro2",
+ "syn",
+]
+
 [[package]]
 name = "proc-macro2"
 version = "1.0.106"
@@ -163,6 +350,37 @@ dependencies = [
  "proc-macro2",
 ]
 
+[[package]]
+name = "r-efi"
+version = "6.0.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "f8dcc9c7d52a811697d2151c701e0d08956f92b0e24136cf4cf27b57a6a0d9bf"
+
+[[package]]
+name = "regex-automata"
+version = "0.4.14"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "6e1dd4122fc1595e8162618945476892eefca7b88c52820e74af6262213cae8f"
+
+[[package]]
+name = "rustix"
+version = "1.1.4"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "b6fe4565b9518b83ef4f91bb47ce29620ca828bd32cb7e408f0062e9930ba190"
+dependencies = [
+ "bitflags",
+ "errno",
+ "libc",
+ "linux-raw-sys",
+ "windows-sys",
+]
+
+[[package]]
+name = "semver"
+version = "1.0.28"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "8a7852d02fc848982e0c167ef163aaff9cd91dc640ba85e263cb1ce46fae51cd"
+
 [[package]]
 name = "serde"
 version = "1.0.228"
@@ -223,6 +441,25 @@ dependencies = [
  "unicode-ident",
 ]
 
+[[package]]
+name = "tempfile"
+version = "3.27.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "32497e9a4c7b38532efcdebeef879707aa9f794296a4f0244f6f69e9bc8574bd"
+dependencies = [
+ "fastrand",
+ "getrandom",
+ "once_cell",
+ "rustix",
+ "windows-sys",
+]
+
+[[package]]
+name = "termtree"
+version = "0.5.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "8f50febec83f5ee1df3015341d8bd429f2d1cc62bcba7ea2076759d315084683"
+
 [[package]]
 name = "thiserror"
 version = "1.0.69"
@@ -249,12 +486,79 @@ version = "1.0.24"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "e6e4313cd5fcd3dad5cafa179702e2b244f760991f45397d14d4ebf38247da75"
 
+[[package]]
+name = "unicode-xid"
+version = "0.2.6"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "ebc1c04c71510c7f702b52b7c350734c9ff1295c464a03335b00bb84fc54f853"
+
 [[package]]
 name = "utf8parse"
 version = "0.2.2"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "06abde3611657adf66d383f00b093d7faecc7fa57071cce2578660c9f1010821"
 
+[[package]]
+name = "wait-timeout"
+version = "0.2.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "09ac3b126d3914f9849036f826e054cbabdc8519970b8998ddaf3b5bd3c65f11"
+dependencies = [
+ "libc",
+]
+
+[[package]]
+name = "wasip2"
+version = "1.0.2+wasi-0.2.9"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "9517f9239f02c069db75e65f174b3da828fe5f5b945c4dd26bd25d89c03ebcf5"
+dependencies = [
+ "wit-bindgen",
+]
+
+[[package]]
+name = "wasip3"
+version = "0.4.0+wasi-0.3.0-rc-2026-01-06"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "5428f8bf88ea5ddc08faddef2ac4a67e390b88186c703ce6dbd955e1c145aca5"
+dependencies = [
+ "wit-bindgen",
+]
+
+[[package]]
+name = "wasm-encoder"
+version = "0.244.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "990065f2fe63003fe337b932cfb5e3b80e0b4d0f5ff650e6985b1048f62c8319"
+dependencies = [
+ "leb128fmt",
+ "wasmparser",
+]
+
+[[package]]
+name = "wasm-metadata"
+version = "0.244.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "bb0e353e6a2fbdc176932bbaab493762eb1255a7900fe0fea1a2f96c296cc909"
+dependencies = [
+ "anyhow",
+ "indexmap",
+ "wasm-encoder",
+ "wasmparser",
+]
+
+[[package]]
+name = "wasmparser"
+version = "0.244.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "47b807c72e1bac69382b3a6fb3dbe8ea4c0ed87ff5629b8685ae6b9a611028fe"
+dependencies = [
+ "bitflags",
+ "hashbrown 0.15.5",
+ "indexmap",
+ "semver",
+]
+
 [[package]]
 name = "windows-link"
 version = "0.2.1"
@@ -270,6 +574,94 @@ dependencies = [
  "windows-link",
 ]
 
+[[package]]
+name = "wit-bindgen"
+version = "0.51.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "d7249219f66ced02969388cf2bb044a09756a083d0fab1e566056b04d9fbcaa5"
+dependencies = [
+ "wit-bindgen-rust-macro",
+]
+
+[[package]]
+name = "wit-bindgen-core"
+version = "0.51.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "ea61de684c3ea68cb082b7a88508a8b27fcc8b797d738bfc99a82facf1d752dc"
+dependencies = [
+ "anyhow",
+ "heck",
+ "wit-parser",
+]
+
+[[package]]
+name = "wit-bindgen-rust"
+version = "0.51.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "b7c566e0f4b284dd6561c786d9cb0142da491f46a9fbed79ea69cdad5db17f21"
+dependencies = [
+ "anyhow",
+ "heck",
+ "indexmap",
+ "prettyplease",
+ "syn",
+ "wasm-metadata",
+ "wit-bindgen-core",
+ "wit-component",
+]
+
+[[package]]
+name = "wit-bindgen-rust-macro"
+version = "0.51.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "0c0f9bfd77e6a48eccf51359e3ae77140a7f50b1e2ebfe62422d8afdaffab17a"
+dependencies = [
+ "anyhow",
+ "prettyplease",
+ "proc-macro2",
+ "quote",
+ "syn",
+ "wit-bindgen-core",
+ "wit-bindgen-rust",
+]
+
+[[package]]
+name = "wit-component"
+version = "0.244.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "9d66ea20e9553b30172b5e831994e35fbde2d165325bec84fc43dbf6f4eb9cb2"
+dependencies = [
+ "anyhow",
+ "bitflags",
+ "indexmap",
+ "log",
+ "serde",
+ "serde_derive",
+ "serde_json",
+ "wasm-encoder",
+ "wasm-metadata",
+ "wasmparser",
+ "wit-parser",
+]
+
+[[package]]
+name = "wit-parser"
+version = "0.244.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "ecc8ac4bc1dc3381b7f59c34f00b67e18f910c2c0f50015669dde7def656a736"
+dependencies = [
+ "anyhow",
+ "id-arena",
+ "indexmap",
+ "log",
+ "semver",
+ "serde",
+ "serde_derive",
+ "serde_json",
+ "unicode-xid",
+ "wasmparser",
+]
+
 [[package]]
 name = "zmij"
 version = "1.0.21"
diff --git a/Cargo.toml b/Cargo.toml
index a12c835..8816971 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -9,3 +9,7 @@ clap = { version = "4.5", features = ["derive"] }
 serde = { version = "1.0", features = ["derive"] }
 serde_json = "1.0"
 thiserror = "1.0"
+
+[dev-dependencies]
+assert_cmd = "2.0"
+tempfile = "3.10"
diff --git a/src/lib.rs b/src/lib.rs
index b2e6849..9937178 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -1,9 +1,33 @@
+use std::path::Path;
+
+use clap::Parser;
+
 pub mod cli;
 pub mod error;
 pub mod model;
 pub mod output;
 pub mod render;
 
+use crate::cli::{Cli, Commands, OutputFormat};
+use crate::output::write_output;
+use crate::render::json::{parse_json, render_json};
+use crate::render::markdown::render_markdown;
+
 pub fn run() -> anyhow::Result<()> {
+    let cli = Cli::parse();
+
+    match cli.command {
+        Commands::RenderMd(args) => {
+            let raw = std::fs::read_to_string(&args.input)?;
+            let doc = parse_json(&raw)?;
+            let md = render_markdown(&doc);
+            write_output(args.out.as_deref().map(Path::new), &md)?;
+        }
+        Commands::Fetch(_args) => {
+            let _ = OutputFormat::Markdown;
+            let _ = render_json;
+        }
+    }
+
     Ok(())
 }
diff --git a/src/render/json.rs b/src/render/json.rs
new file mode 100644
index 0000000..56f90f3
--- /dev/null
+++ b/src/render/json.rs
@@ -0,0 +1,9 @@
+use crate::model::PrReviewDocument;
+
+pub fn render_json(doc: &PrReviewDocument) -> anyhow::Result<String> {
+    Ok(serde_json::to_string_pretty(doc)?)
+}
+
+pub fn parse_json(input: &str) -> anyhow::Result<PrReviewDocument> {
+    Ok(serde_json::from_str(input)?)
+}
diff --git a/src/render/mod.rs b/src/render/mod.rs
index 163a4fb..b495aed 100644
--- a/src/render/mod.rs
+++ b/src/render/mod.rs
@@ -1 +1,2 @@
+pub mod json;
 pub mod markdown;
diff --git a/tests/cli_parse_tests.rs b/tests/cli_parse_tests.rs
index 508b07c..6aedaf0 100644
--- a/tests/cli_parse_tests.rs
+++ b/tests/cli_parse_tests.rs
@@ -16,13 +16,7 @@ fn parse_fetch_default_format() {
 
 #[test]
 fn parse_render_md_requires_input() {
-    let cli = Cli::try_parse_from([
-        "gitea-pr-review",
-        "render-md",
-        "--in",
-        "sample.json",
-    ])
-    .unwrap();
+    let cli = Cli::try_parse_from(["gitea-pr-review", "render-md", "--in", "sample.json"]).unwrap();
 
     match cli.command {
         Commands::RenderMd(args) => {
diff --git a/tests/e2e_smoke_tests.rs b/tests/e2e_smoke_tests.rs
new file mode 100644
index 0000000..a024bc4
--- /dev/null
+++ b/tests/e2e_smoke_tests.rs
@@ -0,0 +1,94 @@
+use assert_cmd::Command;
+use tempfile::NamedTempFile;
+
+#[test]
+fn render_md_reads_json_and_outputs_markdown_to_stdout() {
+    let input = NamedTempFile::new().unwrap();
+    std::fs::write(
+        input.path(),
+        r#"{
+  "meta": {
+    "repo": "org/repo",
+    "pr_index": 1,
+    "title": "t",
+    "state": "open",
+    "author": "a",
+    "base_branch": "main",
+    "head_branch": "f",
+    "created_at": "2026-04-08T10:00:00Z",
+    "updated_at": "2026-04-08T11:00:00Z",
+    "merged_at": null
+  },
+  "commits": [],
+  "diff_stat": {
+    "files_changed": 0,
+    "additions": 0,
+    "deletions": 0,
+    "files": []
+  },
+  "reviews": [],
+  "threads": []
+}"#,
+    )
+    .unwrap();
+
+    let mut cmd = Command::cargo_bin("gitea-pr-review").unwrap();
+    let assert = cmd
+        .args(["render-md", "--in", input.path().to_str().unwrap()])
+        .assert()
+        .success();
+
+    let stdout = String::from_utf8(assert.get_output().stdout.clone()).unwrap();
+    assert!(stdout.contains("# org/repo `#1` t"));
+    assert!(stdout.contains("## Metadata"));
+}
+
+#[test]
+fn render_md_writes_to_out_file_when_requested() {
+    let input = NamedTempFile::new().unwrap();
+    std::fs::write(
+        input.path(),
+        r#"{
+  "meta": {
+    "repo": "org/repo",
+    "pr_index": 2,
+    "title": "t2",
+    "state": "open",
+    "author": "a",
+    "base_branch": "main",
+    "head_branch": "f",
+    "created_at": "2026-04-08T10:00:00Z",
+    "updated_at": "2026-04-08T11:00:00Z",
+    "merged_at": null
+  },
+  "commits": [],
+  "diff_stat": {
+    "files_changed": 0,
+    "additions": 0,
+    "deletions": 0,
+    "files": []
+  },
+  "reviews": [],
+  "threads": []
+}"#,
+    )
+    .unwrap();
+
+    let output = NamedTempFile::new().unwrap();
+
+    Command::cargo_bin("gitea-pr-review")
+        .unwrap()
+        .args([
+            "render-md",
+            "--in",
+            input.path().to_str().unwrap(),
+            "--out",
+            output.path().to_str().unwrap(),
+        ])
+        .assert()
+        .success();
+
+    let written = std::fs::read_to_string(output.path()).unwrap();
+    assert!(written.contains("# org/repo `#2` t2"));
+    assert!(written.contains("## Metadata"));
+}
diff --git a/tests/render_json_tests.rs b/tests/render_json_tests.rs
index 9e77cea..95fa8a6 100644
--- a/tests/render_json_tests.rs
+++ b/tests/render_json_tests.rs
@@ -1,4 +1,6 @@
-use gitea_pr_review::model::{CommentItem, CommentThread, DiffStat, FileStat, PrMeta, PrReviewDocument};
+use gitea_pr_review::model::{
+    CommentItem, CommentThread, DiffStat, FileStat, PrMeta, PrReviewDocument,
+};
 
 #[test]
 fn model_json_roundtrip() {