Skip to content

Output is truncated at 65536 bytes when piped to another process #23

Open
Open
Output is truncated at 65536 bytes when piped to another process#23
#246 (+2)

Description

@ZoltanLajosKis
ZoltanLajosKis
opened on Jan 28, 2026

When I pipe the output of an MCP tool call to another process, it gets truncated at 65536 bytes. When the output is a tty or a file, the whole output is received.

❯ mcp-cli call dummy-mcp text 2>/dev/null | wc -c
65536
❯ mcp-cli call dummy-mcp text 2>/dev/null > /tmp/dummy-mcp-text; wc -c /tmp/dummy-mcp-text
200141 /tmp/dummy-mcp-text

Dummy MCP server (FastMCP 3.0.0b1) for testing:

fromfastmcpimportFastMCPmcp=FastMCP("dummy-mcp")
@mcp.tooldeftext() ->str:
return"x"*100000if__name__=="__main__":
mcp.run()

Metadata

Metadata

Assignees

No one assigned

    Labels

    No labels
    No labels

    Projects

    No projects

      Milestone

      No milestone

      Relationships

      None yet

      Development

      No branches or pull requests

      Issue actions

      , 'i'); if (__m === '*' || __re.test(location.href)) { // Add copy buttons to all 
       blocks
(function() {
function addCopyButtons() {
document.querySelectorAll('pre code').forEach(function(codeBlock) {
if (codeBlock.parentElement.hasAttribute('data-copy-added')) return;
codeBlock.parentElement.setAttribute('data-copy-added', 'true');
var btn = document.createElement('button');
btn.textContent = 'Copy';
btn.style.cssText = 'position:absolute;top:4px;right:4px;padding:2px 8px;font-size:11px;background:#4ecdc4;border:none;border-radius:4px;color:#1a1a2e;cursor:pointer;opacity:0.7;transition:opacity 0.2s;';
btn.onmouseover = function() { this.style.opacity = '1'; };
btn.onmouseout = function() { this.style.opacity = '0.7'; };
btn.onclick = function() {
navigator.clipboard.writeText(codeBlock.textContent).then(function() {
btn.textContent = 'Copied!';
setTimeout(function() { btn.textContent = 'Copy'; }, 1500);
});
};
codeBlock.parentElement.style.position = 'relative';
codeBlock.parentElement.appendChild(btn);
});
}
addCopyButtons();
// Re-run on dynamic content
var observer = new MutationObserver(addCopyButtons);
observer.observe(document.body, { childList: true, subtree: true });
})();
}
} catch(__e) { console.warn('[Userscript:Add Copy Buttons to Code Blocks]', __e); }
})();
(function(){
try {
var __m = "github.com";
var __re = new RegExp('^' + "github\\.com" + '
Output is truncated at 65536 bytes when piped to another process · Issue #23 · philschmid/mcp-cli · GitHub
      Skip to content
      Output is truncated at 65536 bytes when piped to another process #23
      Open
      Open
      Output is truncated at 65536 bytes when piped to another process#23
      #246 (+2)
      Description
      @ZoltanLajosKis
      ZoltanLajosKis
      opened on Jan 28, 2026
      When I pipe the output of an MCP tool call to another process, it gets truncated at 65536 bytes. When the output is a tty or a file, the whole output is received.
      ❯ mcp-cli call dummy-mcp text 2>/dev/null | wc -c
65536
❯ mcp-cli call dummy-mcp text 2>/dev/null > /tmp/dummy-mcp-text; wc -c /tmp/dummy-mcp-text
200141 /tmp/dummy-mcp-text
      Dummy MCP server (FastMCP 3.0.0b1) for testing:
      fromfastmcpimportFastMCPmcp=FastMCP("dummy-mcp")
@mcp.tooldeftext() ->str:
return"x"*100000if__name__=="__main__":
mcp.run()
      Metadata
      Metadata
      Assignees
      No one assigned
        Labels
        No labels
        No labels
        Projects
        No projects
          Milestone
          No milestone
          Relationships
          None yet
          Development
          No branches or pull requests
          Issue actions
          
, 'i');
if (__m === '*' || __re.test(location.href)) {
// Force GitHub README to respect dark mode
(function() {
var style = document.createElement('style');
style.textContent = '
.markdown-body {
color-scheme: dark light;
}
.markdown-body pre { background: #161b22 !important; }
.markdown-body code { background: rgba(110, 118, 129, 0.4) !important; }
.markdown-body table th, .markdown-body table td { border-color: #30363d !important; }
.markdown-body img { background: #0d1117; }
.markdown-body blockquote { border-left-color: #8b949e; }
.markdown-body hr { border-color: #30363d; }
';
document.head.appendChild(style);
})();
}
} catch(__e) { console.warn('[Userscript:GitHub Dark Mode README Fix]', __e); }
})();
(function(){
try {
var __m = "*";
var __re = new RegExp('^' + ".*" + '
Output is truncated at 65536 bytes when piped to another process · Issue #23 · philschmid/mcp-cli · GitHub
          Skip to content
          Output is truncated at 65536 bytes when piped to another process #23
          Open
          Open
          Output is truncated at 65536 bytes when piped to another process#23
          #246 (+2)
          Description
          @ZoltanLajosKis
          ZoltanLajosKis
          opened on Jan 28, 2026
          When I pipe the output of an MCP tool call to another process, it gets truncated at 65536 bytes. When the output is a tty or a file, the whole output is received.
          ❯ mcp-cli call dummy-mcp text 2>/dev/null | wc -c
65536
❯ mcp-cli call dummy-mcp text 2>/dev/null > /tmp/dummy-mcp-text; wc -c /tmp/dummy-mcp-text
200141 /tmp/dummy-mcp-text
          Dummy MCP server (FastMCP 3.0.0b1) for testing:
          fromfastmcpimportFastMCPmcp=FastMCP("dummy-mcp")
@mcp.tooldeftext() ->str:
return"x"*100000if__name__=="__main__":
mcp.run()
          Metadata
          Metadata
          Assignees
          No one assigned
            Labels
            No labels
            No labels
            Projects
            No projects
              Milestone
              No milestone
              Relationships
              None yet
              Development
              No branches or pull requests
              Issue actions
              
, 'i');
if (__m === '*' || __re.test(location.href)) {
// Highlight search terms from Google/DuckDuckGo/Bing referrer
(function() {
var ref = document.referrer;
var terms = [];
if (ref.includes('google.com') || ref.includes('duckduckgo.com') || ref.includes('bing.com')) {
var url = new URL(ref);
var q = url.searchParams.get('q') || url.searchParams.get('p');
if (q) {
terms = q.split(/\s+/).filter(function(t) { return t.length > 2; });
}
}
if (terms.length === 0) return;
var style = document.createElement('style');
style.textContent = '.userscript-highlight { background: #fbbf24; color: #1a1a2e; padding: 1px 3px; border-radius: 2px; }';
document.head.appendChild(style);
function highlight(node) {
if (node.nodeType === 3) { // text node
var text = node.textContent;
var found = false;
terms.forEach(function(term) {
var regex = new RegExp('(' + term.replace(/[.*+?^${}()|[\]\\]/g, '\\') + ')', 'gi');
if (regex.test(text)) {
found = true;
var frag = document.createDocumentFragment();
var parts = text.split(regex);
parts.forEach(function(part, i) {
if (i % 2 === 0) {
frag.appendChild(document.createTextNode(part));
} else {
var span = document.createElement('span');
span.className = 'userscript-highlight';
span.textContent = part;
frag.appendChild(span);
}
});
node.parentNode.replaceChild(frag, node);
}
});
} else if (node.nodeType === 1 && node.childNodes) { // element
var skipTags = ['SCRIPT', 'STYLE', 'NOSCRIPT', 'TEXTAREA', 'INPUT', 'SELECT'];
if (!skipTags.includes(node.tagName)) {
Array.from(node.childNodes).forEach(highlight);
}
}
}
highlight(document.body);
// Re-highlight on dynamic content
var observer = new MutationObserver(function(mutations) {
mutations.forEach(function(m) {
m.addedNodes.forEach(function(node) {
if (node.nodeType === 1 || node.nodeType === 3) highlight(node);
});
});
});
observer.observe(document.body, { childList: true, subtree: true });
})();
}
} catch(__e) { console.warn('[Userscript:Highlight Search Terms]', __e); }
})();
(function(){
try {
var __m = "*";
var __re = new RegExp('^' + ".*" + '
Output is truncated at 65536 bytes when piped to another process · Issue #23 · philschmid/mcp-cli · GitHub
              Skip to content
              Output is truncated at 65536 bytes when piped to another process #23
              Open
              Open
              Output is truncated at 65536 bytes when piped to another process#23
              #246 (+2)
              Description
              @ZoltanLajosKis
              ZoltanLajosKis
              opened on Jan 28, 2026
              When I pipe the output of an MCP tool call to another process, it gets truncated at 65536 bytes. When the output is a tty or a file, the whole output is received.
              ❯ mcp-cli call dummy-mcp text 2>/dev/null | wc -c
65536
❯ mcp-cli call dummy-mcp text 2>/dev/null > /tmp/dummy-mcp-text; wc -c /tmp/dummy-mcp-text
200141 /tmp/dummy-mcp-text
              Dummy MCP server (FastMCP 3.0.0b1) for testing:
              fromfastmcpimportFastMCPmcp=FastMCP("dummy-mcp")
@mcp.tooldeftext() ->str:
return"x"*100000if__name__=="__main__":
mcp.run()
              Metadata
              Metadata
              Assignees
              No one assigned
                Labels
                No labels
                No labels
                Projects
                No projects
                  Milestone
                  No milestone
                  Relationships
                  None yet
                  Development
                  No branches or pull requests
                  Issue actions
                  
, 'i');
if (__m === '*' || __re.test(location.href)) {
// Strip utm_, fbclid, gclid, etc. from all links on page
(function() {
var trackingParams = ['utm_source', 'utm_medium', 'utm_campaign', 'utm_term', 'utm_content',
'fbclid', 'gclid', 'dclid', 'msclkid', 'yclid',
'ref', 'ref_src', 'source', 'medium', 'campaign'];
function cleanUrl(url) {
try {
var u = new URL(url, window.location.origin);
var changed = false;
trackingParams.forEach(function(p) {
if (u.searchParams.has(p)) {
u.searchParams.delete(p);
changed = true;
}
});
return changed ? u.toString() : url;
} catch (e) {
return url;
}
}
function cleanLinks() {
document.querySelectorAll('a[href]').forEach(function(a) {
var clean = cleanUrl(a.href);
if (clean !== a.href) a.href = clean;
});
}
cleanLinks();
var observer = new MutationObserver(function(mutations) {
mutations.forEach(function(m) {
m.addedNodes.forEach(function(node) {
if (node.nodeType === 1) {
if (node.tagName === 'A') cleanLinks();
node.querySelectorAll('a[href]').forEach(function(a) {
var clean = cleanUrl(a.href);
if (clean !== a.href) a.href = clean;
});
}
});
});
});
observer.observe(document.body, { childList: true, subtree: true });
})();
}
} catch(__e) { console.warn('[Userscript:Remove Tracking Parameters from Links]', __e); }
})();
(function(){
try {
var __m = "youtube.com";
var __re = new RegExp('^' + "youtube\\.com" + '
Output is truncated at 65536 bytes when piped to another process · Issue #23 · philschmid/mcp-cli · GitHub
                  Skip to content
                  Output is truncated at 65536 bytes when piped to another process #23
                  Open
                  Open
                  Output is truncated at 65536 bytes when piped to another process#23
                  #246 (+2)
                  Description
                  @ZoltanLajosKis
                  ZoltanLajosKis
                  opened on Jan 28, 2026
                  When I pipe the output of an MCP tool call to another process, it gets truncated at 65536 bytes. When the output is a tty or a file, the whole output is received.
                  ❯ mcp-cli call dummy-mcp text 2>/dev/null | wc -c
65536
❯ mcp-cli call dummy-mcp text 2>/dev/null > /tmp/dummy-mcp-text; wc -c /tmp/dummy-mcp-text
200141 /tmp/dummy-mcp-text
                  Dummy MCP server (FastMCP 3.0.0b1) for testing:
                  fromfastmcpimportFastMCPmcp=FastMCP("dummy-mcp")
@mcp.tooldeftext() ->str:
return"x"*100000if__name__=="__main__":
mcp.run()
                  Metadata
                  Metadata
                  Assignees
                  No one assigned
                    Labels
                    No labels
                    No labels
                    Projects
                    No projects
                      Milestone
                      No milestone
                      Relationships
                      None yet
                      Development
                      No branches or pull requests
                      Issue actions
                      
, 'i');
if (__m === '*' || __re.test(location.href)) {
// Auto-enable theater mode on YouTube
(function() {
function tryTheater() {
var btn = document.querySelector('button[aria-label="Theater mode"], ytd-player #player button[title="Theater mode"]');
if (btn && !btn.classList.contains('activated')) {
btn.click();
}
}
// Try immediately
tryTheater();
// Try after navigation (SPA)
var lastUrl = location.href;
setInterval(function() {
if (location.href !== lastUrl) {
lastUrl = location.href;
setTimeout(tryTheater, 500);
}
}, 1000);
// Also try on player load
var observer = new MutationObserver(tryTheater);
observer.observe(document.body, { childList: true, subtree: true });
})();
}
} catch(__e) { console.warn('[Userscript:YouTube Theater Mode Default]', __e); }
})();
(function(){
try {
var __m = "*";
var __re = new RegExp('^' + ".*" + '
Output is truncated at 65536 bytes when piped to another process · Issue #23 · philschmid/mcp-cli · GitHub
                      Skip to content
                      Output is truncated at 65536 bytes when piped to another process #23
                      Open
                      Open
                      Output is truncated at 65536 bytes when piped to another process#23
                      #246 (+2)
                      Description
                      @ZoltanLajosKis
                      ZoltanLajosKis
                      opened on Jan 28, 2026
                      When I pipe the output of an MCP tool call to another process, it gets truncated at 65536 bytes. When the output is a tty or a file, the whole output is received.
                      ❯ mcp-cli call dummy-mcp text 2>/dev/null | wc -c
65536
❯ mcp-cli call dummy-mcp text 2>/dev/null > /tmp/dummy-mcp-text; wc -c /tmp/dummy-mcp-text
200141 /tmp/dummy-mcp-text
                      Dummy MCP server (FastMCP 3.0.0b1) for testing:
                      fromfastmcpimportFastMCPmcp=FastMCP("dummy-mcp")
@mcp.tooldeftext() ->str:
return"x"*100000if__name__=="__main__":
mcp.run()
                      Metadata
                      Metadata
                      Assignees
                      No one assigned
                        Labels
                        No labels
                        No labels
                        Projects
                        No projects
                          Milestone
                          No milestone
                          Relationships
                          None yet
                          Development
                          No branches or pull requests
                          Issue actions
                          
, 'i');
if (__m === '*' || __re.test(location.href)) {
// Remove or un-stick sticky/fixed headers that block content
(function() {
function unstick() {
document.querySelectorAll('header, nav, [role="banner"], .header, .navbar, .sticky, .fixed-top, [style*="position: fixed"], [style*="position:sticky"]').forEach(function(el) {
if (el.style.position === 'fixed' || el.style.position === 'sticky' || getComputedStyle(el).position === 'fixed' || getComputedStyle(el).position === 'sticky') {
el.style.position = 'static';
el.style.top = 'auto';
el.style.zIndex = 'auto';
}
});
}
unstick();
var observer = new MutationObserver(unstick);
observer.observe(document.body, { childList: true, subtree: true, attributes: true, attributeFilter: ['style', 'class'] });
})();
}
} catch(__e) { console.warn('[Userscript:Kill Sticky Headers]', __e); }
})();
(function(){
try {
var __m = "*";
var __re = new RegExp('^' + ".*" + '
Output is truncated at 65536 bytes when piped to another process · Issue #23 · philschmid/mcp-cli · GitHub
                          Skip to content
                          Output is truncated at 65536 bytes when piped to another process #23
                          Open
                          Open
                          Output is truncated at 65536 bytes when piped to another process#23
                          #246 (+2)
                          Description
                          @ZoltanLajosKis
                          ZoltanLajosKis
                          opened on Jan 28, 2026
                          When I pipe the output of an MCP tool call to another process, it gets truncated at 65536 bytes. When the output is a tty or a file, the whole output is received.
                          ❯ mcp-cli call dummy-mcp text 2>/dev/null | wc -c
65536
❯ mcp-cli call dummy-mcp text 2>/dev/null > /tmp/dummy-mcp-text; wc -c /tmp/dummy-mcp-text
200141 /tmp/dummy-mcp-text
                          Dummy MCP server (FastMCP 3.0.0b1) for testing:
                          fromfastmcpimportFastMCPmcp=FastMCP("dummy-mcp")
@mcp.tooldeftext() ->str:
return"x"*100000if__name__=="__main__":
mcp.run()
                          Metadata
                          Metadata
                          Assignees
                          No one assigned
                            Labels
                            No labels
                            No labels
                            Projects
                            No projects
                              Milestone
                              No milestone
                              Relationships
                              None yet
                              Development
                              No branches or pull requests
                              Issue actions
                              
, 'i');
if (__m === '*' || __re.test(location.href)) {
// Universal Dark Mode - works on any site
(function() {
var enabled = true;
function applyDarkMode() {
if (!enabled) return;
// Create style element if it doesn't exist
var style = document.getElementById('universal-dark-mode-style');
if (!style) {
style = document.createElement('style');
style.id = 'universal-dark-mode-style';
document.head.appendChild(style);
}
// Dark mode CSS - inverts colors but preserves images/video
style.textContent = '
/* Invert everything except media */
html {
filter: invert(1) hue-rotate(180deg) !important;
background: #1a1a2e !important;
}
/* Restore images, videos, iframes, canvas */
img, video, iframe, canvas, svg, picture, [style*="background-image"] {
filter: invert(1) hue-rotate(180deg) !important;
}
/* Preserve specific elements that should not be inverted */
.no-dark-mode, .no-dark-mode *,
[data-theme="light"], [data-theme="light"],
.ace_editor, .ace_editor *,
.CodeMirror, .CodeMirror *,
.monaco-editor, .monaco-editor *,
.markdown-body pre, .markdown-body pre *,
.highlight, .highlight *,
pre code, pre code * {
filter: none !important;
}
/* Fix common UI elements */
.modal, .popup, .dropdown-menu, .tooltip, .popover {
filter: invert(1) hue-rotate(180deg) !important;
background: #2d2d44 !important;
border-color: #444 !important;
}
/* Scrollbars */
::-webkit-scrollbar { background: #1a1a2e !important; }
::-webkit-scrollbar-thumb { background: #444 !important; }
::-webkit-scrollbar-thumb:hover { background: #555 !important; }
/* Selection */
::selection { background: #4ecdc4 !important; color: #1a1a2e !important; }
::-moz-selection { background: #4ecdc4 !important; color: #1a1a2e !important; }
';
}
function removeDarkMode() {
var style = document.getElementById('universal-dark-mode-style');
if (style) style.remove();
}
// Toggle with Alt+Shift+D
document.addEventListener('keydown', function(e) {
if (e.altKey && e.shiftKey && e.key === 'D') {
e.preventDefault();
enabled = !enabled;
if (enabled) {
applyDarkMode();
console.log('[Universal Dark Mode] Enabled');
} else {
removeDarkMode();
console.log('[Universal Dark Mode] Disabled');
}
}
});
// Apply on load
applyDarkMode();
// Re-apply on dynamic content
var observer = new MutationObserver(function(mutations) {
if (enabled && !document.getElementById('universal-dark-mode-style')) {
applyDarkMode();
}
});
observer.observe(document.head, { childList: true });
console.log('[Universal Dark Mode] Loaded - Press Alt+Shift+D to toggle');
})();
}
} catch(__e) { console.warn('[Userscript:Universal Dark Mode]', __e); }
})();
})();
Output is truncated at 65536 bytes when piped to another process · Issue #23 · philschmid/mcp-cli · GitHub
                              Skip to content
                              Output is truncated at 65536 bytes when piped to another process #23
                              Open
                              Open
                              Output is truncated at 65536 bytes when piped to another process#23
                              #246 (+2)
                              Description
                              @ZoltanLajosKis
                              ZoltanLajosKis
                              opened on Jan 28, 2026
                              When I pipe the output of an MCP tool call to another process, it gets truncated at 65536 bytes. When the output is a tty or a file, the whole output is received.
                              ❯ mcp-cli call dummy-mcp text 2>/dev/null | wc -c
65536
❯ mcp-cli call dummy-mcp text 2>/dev/null > /tmp/dummy-mcp-text; wc -c /tmp/dummy-mcp-text
200141 /tmp/dummy-mcp-text
                              Dummy MCP server (FastMCP 3.0.0b1) for testing:
                              fromfastmcpimportFastMCPmcp=FastMCP("dummy-mcp")
@mcp.tooldeftext() ->str:
return"x"*100000if__name__=="__main__":
mcp.run()
                              Metadata
                              Metadata
                              Assignees
                              No one assigned
                                Labels
                                No labels
                                No labels
                                Projects
                                No projects
                                  Milestone
                                  No milestone
                                  Relationships
                                  None yet
                                  Development
                                  No branches or pull requests
                                  Issue actions