diff --git a/Cargo.lock b/Cargo.lock
index fcf55f4..1cd28e4 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -2,6 +2,34 @@
 # It is not intended for manual editing.
 version = 4
 
+[[package]]
+name = "ahash"
+version = "0.8.12"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "5a15f179cd60c4584b8a8c596927aadc462e27f2ca70c04e0071964a73ba7a75"
+dependencies = [
+ "cfg-if",
+ "getrandom 0.3.4",
+ "once_cell",
+ "version_check",
+ "zerocopy",
+]
+
+[[package]]
+name = "aho-corasick"
+version = "1.1.4"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "ddd31a130427c27518df266943a5308ed92d4b226cc639f5a8f1002816174301"
+dependencies = [
+ "memchr",
+]
+
+[[package]]
+name = "allocator-api2"
+version = "0.2.21"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "683d7910e743518b0e34f1186f92494becacb047c7b6bf616c96772180fef923"
+
 [[package]]
 name = "android_system_properties"
 version = "0.1.5"
@@ -67,6 +95,12 @@ version = "1.5.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "c08606f8c3cbf4ce6ec8e28fb0014a2c086708fe954eaa885384a6165172e7e8"
 
+[[package]]
+name = "base64"
+version = "0.22.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "72b3254f16251a8381aa12e40e3c4d2f0199f8c6508fbecb9d91f575e0fbb8c6"
+
 [[package]]
 name = "bitflags"
 version = "2.10.0"
@@ -129,6 +163,15 @@ dependencies = [
  "windows-link",
 ]
 
+[[package]]
+name = "chumsky"
+version = "0.9.3"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "8eebd66744a15ded14960ab4ccdbfb51ad3b81f51f3f04a80adac98c985396c9"
+dependencies = [
+ "hashbrown 0.14.5",
+]
+
 [[package]]
 name = "clap"
 version = "4.5.55"
@@ -237,6 +280,18 @@ dependencies = [
  "syn",
 ]
 
+[[package]]
+name = "dyn-clone"
+version = "1.0.20"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "d0881ea181b1df73ff77ffaaf9c7544ecc11e82fba9b5f27b262a3c73a332555"
+
+[[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"
@@ -360,12 +415,34 @@ dependencies = [
  "wasip2",
 ]
 
+[[package]]
+name = "hashbrown"
+version = "0.14.5"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "e5274423e17b7c9fc20b6e7e208532f9b19825d82dfd615708b70edd83df41f1"
+dependencies = [
+ "ahash",
+ "allocator-api2",
+]
+
+[[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 = "hifijson"
+version = "0.2.3"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "0a7763b98ba8a24f59e698bf9ab197e7676c640d6455d1580b4ce7dc560f0f0d"
+
 [[package]]
 name = "http"
 version = "1.4.0"
@@ -508,6 +585,16 @@ dependencies = [
  "icu_properties",
 ]
 
+[[package]]
+name = "indexmap"
+version = "2.13.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "7714e70437a7dc3ac8eb7e6f8df75fd8eb422675fc7678aff7364301092b1017"
+dependencies = [
+ "equivalent",
+ "hashbrown 0.16.1",
+]
+
 [[package]]
 name = "is_terminal_polyfill"
 version = "1.70.2"
@@ -520,6 +607,66 @@ version = "1.0.17"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "92ecc6618181def0457392ccd0ee51198e065e016d1d527a7ac1b6dc7c1f09d2"
 
+[[package]]
+name = "jaq-core"
+version = "1.5.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "d6fda09ee08c84c81293fdf811d9ebaa87b327557b5391f290c926d728c2ddd4"
+dependencies = [
+ "aho-corasick",
+ "base64",
+ "chrono",
+ "hifijson",
+ "jaq-interpret",
+ "libm",
+ "log",
+ "regex",
+ "urlencoding",
+]
+
+[[package]]
+name = "jaq-interpret"
+version = "1.5.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "2fe95ec3c24af3fd9f3dd1091593f5e49b003a66c496a8aa39d764d0a06ae17b"
+dependencies = [
+ "ahash",
+ "dyn-clone",
+ "hifijson",
+ "indexmap",
+ "jaq-syn",
+ "once_cell",
+ "serde_json",
+]
+
+[[package]]
+name = "jaq-parse"
+version = "1.0.3"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "0346d7d3146cdda8acd929581f3d6626a332356c74d5c95aeaffaac2eb6dee82"
+dependencies = [
+ "chumsky",
+ "jaq-syn",
+]
+
+[[package]]
+name = "jaq-std"
+version = "1.6.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "bfbaa55578fd3b70433b594a370741e0c364e4afff92cc0099623fce87311bc1"
+dependencies = [
+ "jaq-syn",
+]
+
+[[package]]
+name = "jaq-syn"
+version = "1.6.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "1ba44fe4428c71304604261ecbae047ee9cfb60c4f1a6bd222ebbb31726d3948"
+dependencies = [
+ "serde",
+]
+
 [[package]]
 name = "js-sys"
 version = "0.3.85"
@@ -542,6 +689,12 @@ version = "0.2.180"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "bcc35a38544a891a5f7c865aca548a982ccb3b8650a5b06d0fd33a10283c56fc"
 
+[[package]]
+name = "libm"
+version = "0.2.16"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "b6d2cec3eae94f9f509c767b45932f1ada8350c4bdb85af2fcab4a3c14807981"
+
 [[package]]
 name = "linux-raw-sys"
 version = "0.11.0"
@@ -569,6 +722,12 @@ version = "0.4.29"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "5e5032e24019045c762d3c0f28f5b6b8bbf38563a65908389bf7978758920897"
 
+[[package]]
+name = "memchr"
+version = "2.7.6"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "f52b00d39961fc5b2736ea853c9cc86238e165017a493d1d5c8eac6bdc4cc273"
+
 [[package]]
 name = "mio"
 version = "1.1.1"
@@ -799,6 +958,35 @@ dependencies = [
  "bitflags",
 ]
 
+[[package]]
+name = "regex"
+version = "1.12.3"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "e10754a14b9137dd7b1e3e5b0493cc9171fdd105e0ab477f51b72e7f3ac0e276"
+dependencies = [
+ "aho-corasick",
+ "memchr",
+ "regex-automata",
+ "regex-syntax",
+]
+
+[[package]]
+name = "regex-automata"
+version = "0.4.14"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "6e1dd4122fc1595e8162618945476892eefca7b88c52820e74af6262213cae8f"
+dependencies = [
+ "aho-corasick",
+ "memchr",
+ "regex-syntax",
+]
+
+[[package]]
+name = "regex-syntax"
+version = "0.8.9"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "a96887878f22d7bad8a3b6dc5b7440e0ada9a245242924394987b21cf2210a4c"
+
 [[package]]
 name = "rustix"
 version = "1.1.3"
@@ -863,6 +1051,7 @@ source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "9a8e94ea7f378bd32cbbd37198a4a91436180c5bb472411e48b5ec2e2124ae9e"
 dependencies = [
  "serde_core",
+ "serde_derive",
 ]
 
 [[package]]
@@ -885,6 +1074,19 @@ dependencies = [
  "syn",
 ]
 
+[[package]]
+name = "serde_json"
+version = "1.0.149"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "83fc039473c5595ace860d8c4fafa220ff474b3fc6bfdb4293327f1a37e94d86"
+dependencies = [
+ "itoa",
+ "memchr",
+ "serde",
+ "serde_core",
+ "zmij",
+]
+
 [[package]]
 name = "sha1"
 version = "0.10.6"
@@ -1182,6 +1384,12 @@ dependencies = [
  "serde",
 ]
 
+[[package]]
+name = "urlencoding"
+version = "2.1.3"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "daf8dba3b7eb870caf1ddeed7bc9d2a049f3cfdfae7cb521b087cc33ae4c49da"
+
 [[package]]
 name = "utf-8"
 version = "0.7.6"
@@ -1285,6 +1493,11 @@ dependencies = [
  "chrono",
  "clap",
  "futures-util",
+ "jaq-core",
+ "jaq-interpret",
+ "jaq-parse",
+ "jaq-std",
+ "serde_json",
  "tokio",
  "tokio-tungstenite",
  "tracing",
@@ -1542,3 +1755,9 @@ dependencies = [
  "quote",
  "syn",
 ]
+
+[[package]]
+name = "zmij"
+version = "1.0.19"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "3ff05f8caa9038894637571ae6b9e29466c1f4f829d26c9b28f869a29cbe3445"
diff --git a/Cargo.toml b/Cargo.toml
index 89e0c57..dbdf883 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -12,3 +12,8 @@ clap = { version = "4", features = ["derive"] }
 futures-util = "0.3"
 chrono = "0.4"
 url = "2"
+jaq-core = "1"
+jaq-interpret = "1"
+jaq-parse = "1"
+jaq-std = "1"
+serde_json = "1"
diff --git a/src/main.rs b/src/main.rs
index 661cb38..d28ef19 100644
--- a/src/main.rs
+++ b/src/main.rs
@@ -1,10 +1,11 @@
 use std::fs;
 use std::path::PathBuf;
+use std::sync::Arc;
 
 use chrono::Local;
 use clap::Parser;
-use url::{form_urlencoded, Url};
 use futures_util::StreamExt;
+use jaq_interpret::{Ctx, Filter, FilterT, ParseCtx, RcIter, Val};
 use tokio::task::JoinSet;
 use tokio_tungstenite::{
     connect_async_with_config,
@@ -15,6 +16,7 @@ use tokio_tungstenite::{
     },
 };
 use tracing::{debug, error, info, warn, Level};
+use url::{form_urlencoded, Url};
 
 #[derive(Parser)]
 #[command(name = "websocket-debug")]
@@ -35,6 +37,10 @@ struct Args {
     /// Query string parameters to add to all URLs (pre-encoded, e.g., "name=First%20Last&key=value")
     #[arg(short = 'q', long = "query-string-all")]
     query_string_all: Option<String>,
+
+    /// jq expression to evaluate on JSON text messages for logging (e.g., ".message" or ".data.id")
+    #[arg(short = 'j', long = "jaq")]
+    jaq: Option<String>,
 }
 
 #[tokio::main]
@@ -58,6 +64,37 @@ async fn main() -> Result<(), Box<dyn std::error::Error>> {
     fs::create_dir_all(&session_dir)?;
     info!("Created session directory: {}", session_dir.display());
 
+    // Compile jaq filter if provided
+    let jaq_filter: Option<Arc<Filter>> = if let Some(ref expr) = args.jaq {
+        let mut defs = ParseCtx::new(Vec::new());
+        defs.insert_natives(jaq_core::core());
+        defs.insert_defs(jaq_std::std());
+
+        let (parsed, errs) = jaq_parse::parse(expr, jaq_parse::main());
+        if !errs.is_empty() {
+            let err_msgs: Vec<String> = errs.iter().map(|e| format!("{:?}", e)).collect();
+            return Err(format!("Failed to parse jaq expression: {}", err_msgs.join(", ")).into());
+        }
+
+        let parsed = parsed.ok_or("Failed to parse jaq expression")?;
+        let filter = defs.compile(parsed);
+
+        if !defs.errs.is_empty() {
+            return Err(
+                format!(
+                    "Failed to compile jaq expression ({} error(s))",
+                    defs.errs.len()
+                )
+                .into(),
+            );
+        }
+
+        info!("Using jaq filter: {}", expr);
+        Some(Arc::new(filter))
+    } else {
+        None
+    };
+
     // Parse extra query params once if specified
     let extra_params: Vec<(String, String)> = args
         .query_string_all
@@ -216,6 +253,7 @@ async fn main() -> Result<(), Box<dyn std::error::Error>> {
 
     for (letter, url, ws_stream) in connections {
         let session_dir = session_dir.clone();
+        let jaq_filter = jaq_filter.clone();
 
         join_set.spawn(async move {
             let (_, mut read) = ws_stream.split();
@@ -226,10 +264,55 @@ async fn main() -> Result<(), Box<dyn std::error::Error>> {
                     Ok(message) => {
                         match message {
                             Message::Text(text) => {
-                                let preview: String = text.chars().take(50).collect();
-                                let truncated = if text.len() > 50 { "..." } else { "" };
-                                info!("[{}:{}] Text: {}{}", letter, seq_num, preview, truncated);
+                                // Determine what to log based on jaq filter
+                                let log_content = if let Some(ref filter) = jaq_filter {
+                                    match serde_json::from_str::<serde_json::Value>(&text) {
+                                        Ok(json_val) => {
+                                            let inputs = RcIter::new(core::iter::empty());
+                                            let ctx = Ctx::new([], &inputs);
+                                            let out =
+                                                filter.run((ctx, Val::from(json_val)));
+                                            let results: Vec<Result<Val, _>> = out.collect();
 
+                                            let mut output_parts = Vec::new();
+                                            for result in results {
+                                                match result {
+                                                    Ok(val) => {
+                                                        output_parts.push(val.to_string());
+                                                    }
+                                                    Err(e) => {
+                                                        warn!(
+                                                            "[{}:{}] jaq error: {}",
+                                                            letter, seq_num, e
+                                                        );
+                                                    }
+                                                }
+                                            }
+                                            if output_parts.is_empty() {
+                                                "(no output)".to_string()
+                                            } else {
+                                                output_parts.join(", ")
+                                            }
+                                        }
+                                        Err(e) => {
+                                            warn!(
+                                                "[{}:{}] JSON parse error: {}",
+                                                letter, seq_num, e
+                                            );
+                                            let preview: String = text.chars().take(50).collect();
+                                            let truncated = if text.len() > 50 { "..." } else { "" };
+                                            format!("{}{}", preview, truncated)
+                                        }
+                                    }
+                                } else {
+                                    let preview: String = text.chars().take(50).collect();
+                                    let truncated = if text.len() > 50 { "..." } else { "" };
+                                    format!("{}{}", preview, truncated)
+                                };
+
+                                info!("[{}:{}] Text: {}", letter, seq_num, log_content);
+
+                                // Always write full message to file
                                 let filename =
                                     session_dir.join(format!("{}{}.txt", letter, seq_num));
                                 if let Err(e) = fs::write(&filename, &text) {