Client class should throw a custom exception if the capability is unsupported #430

Closed
#1761
Closed
Client class should throw a custom exception if the capability is unsupported#430
#1761
Labels
P3Nice to haves, rare edge casesenhancementRequest for a new feature that's not currently supportedgood first issueGood for newcomers - can be tackled without deep knowledge of the codebase

Description

@rahulkarajgikar
rahulkarajgikar
opened on Apr 30, 2025

Is your feature request related to a problem? Please describe.
Currently, MCP Client class in https://github.com/modelcontextprotocol/typescript-sdk/blob/main/src/client/index.ts throws Error when a capability isn't supported by a server. While building any MCP client applications, this makes it hard to know, when i call client.listPrompts and get back an exception - if the exception was because of an actual failure or because the capability isn't supported

Describe the solution you'd like
Client class should throw a custom exception like UnsupportedCapabilityException when the capability itself isn't supported - this makes it easy to write clients around this logic

Describe alternatives you've considered
Currently i am working around this by grepping the returned exception message to see if it contains the string does not support. This is very brittle and can break easily if the exception message changes

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      , 'i'); if (__m === '*' || __re.test(location.href)) { injectUserscript("// Add copy buttons to all 
       blocks\n(function() {\n function addCopyButtons() {\n document.querySelectorAll('pre code').forEach(function(codeBlock) {\n if (codeBlock.parentElement.hasAttribute('data-copy-added')) return;\n codeBlock.parentElement.setAttribute('data-copy-added', 'true');\n \n var btn = document.createElement('button');\n btn.textContent = 'Copy';\n 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;';\n btn.onmouseover = function() { this.style.opacity = '1'; };\n btn.onmouseout = function() { this.style.opacity = '0.7'; };\n btn.onclick = function() {\n navigator.clipboard.writeText(codeBlock.textContent).then(function() {\n btn.textContent = 'Copied!';\n setTimeout(function() { btn.textContent = 'Copy'; }, 1500);\n });\n };\n codeBlock.parentElement.style.position = 'relative';\n codeBlock.parentElement.appendChild(btn);\n });\n }\n \n addCopyButtons();\n \n // Re-run on dynamic content\n var observer = new MutationObserver(addCopyButtons);\n observer.observe(document.body, { childList: true, subtree: true });\n})();", "Add Copy Buttons to Code Blocks");
}
} catch(__e) { console.warn('[Userscript:Add Copy Buttons to Code Blocks]', __e); }
})();
(function(){
try {
var __m = "github.com";
var __re = new RegExp('^' + "github\\.com" + '

      Skip to content
      Client class should throw a custom exception if the capability is unsupported #430
      Closed
      #1761
      Closed
      Client class should throw a custom exception if the capability is unsupported#430
      #1761
      Labels
      P3Nice to haves, rare edge casesenhancementRequest for a new feature that's not currently supportedgood first issueGood for newcomers - can be tackled without deep knowledge of the codebase
      Description
      @rahulkarajgikar
      rahulkarajgikar
      opened on Apr 30, 2025
      Is your feature request related to a problem? Please describe.
      
Currently, MCP Client class in https://github.com/modelcontextprotocol/typescript-sdk/blob/main/src/client/index.ts throws Error when a capability isn't supported by a server. While building any MCP client applications, this makes it hard to know, when i call client.listPrompts and get back an exception - if the exception was because of an actual failure or because the capability isn't supported
      Describe the solution you'd like
      
Client class should throw a custom exception like UnsupportedCapabilityException when the capability itself isn't supported - this makes it easy to write clients around this logic
      Describe alternatives you've considered
      
Currently i am working around this by grepping the returned exception message to see if it contains the string does not support. This is very brittle and can break easily if the exception message changes
      Metadata
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        Labels
        P3Nice to haves, rare edge casesenhancementRequest for a new feature that's not currently supportedgood first issueGood for newcomers - can be tackled without deep knowledge of the codebase
        Type
        No type
        Projects
        No projects
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          No milestone
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          None yet
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          No branches or pull requests
          Issue actions
          
, 'i');
if (__m === '*' || __re.test(location.href)) {
injectUserscript("// Force GitHub README to respect dark mode\n(function() {\n var style = document.createElement('style');\n style.textContent = '\n .markdown-body {\n color-scheme: dark light;\n }\n .markdown-body pre { background: #161b22 !important; }\n .markdown-body code { background: rgba(110, 118, 129, 0.4) !important; }\n .markdown-body table th, .markdown-body table td { border-color: #30363d !important; }\n .markdown-body img { background: #0d1117; }\n .markdown-body blockquote { border-left-color: #8b949e; }\n .markdown-body hr { border-color: #30363d; }\n ';\n document.head.appendChild(style);\n})();", "GitHub Dark Mode README Fix");
}
} catch(__e) { console.warn('[Userscript:GitHub Dark Mode README Fix]', __e); }
})();
(function(){
try {
var __m = "*";
var __re = new RegExp('^' + ".*" + '

          Skip to content
          Client class should throw a custom exception if the capability is unsupported #430
          Closed
          #1761
          Closed
          Client class should throw a custom exception if the capability is unsupported#430
          #1761
          Labels
          P3Nice to haves, rare edge casesenhancementRequest for a new feature that's not currently supportedgood first issueGood for newcomers - can be tackled without deep knowledge of the codebase
          Description
          @rahulkarajgikar
          rahulkarajgikar
          opened on Apr 30, 2025
          Is your feature request related to a problem? Please describe.
          
Currently, MCP Client class in https://github.com/modelcontextprotocol/typescript-sdk/blob/main/src/client/index.ts throws Error when a capability isn't supported by a server. While building any MCP client applications, this makes it hard to know, when i call client.listPrompts and get back an exception - if the exception was because of an actual failure or because the capability isn't supported
          Describe the solution you'd like
          
Client class should throw a custom exception like UnsupportedCapabilityException when the capability itself isn't supported - this makes it easy to write clients around this logic
          Describe alternatives you've considered
          
Currently i am working around this by grepping the returned exception message to see if it contains the string does not support. This is very brittle and can break easily if the exception message changes
          Metadata
          Metadata
          Assignees
          No one assigned
            Labels
            P3Nice to haves, rare edge casesenhancementRequest for a new feature that's not currently supportedgood first issueGood for newcomers - can be tackled without deep knowledge of the codebase
            Type
            No type
            Projects
            No projects
              Milestone
              No milestone
              Relationships
              None yet
              Development
              No branches or pull requests
              Issue actions
              
, 'i');
if (__m === '*' || __re.test(location.href)) {
injectUserscript("// Highlight search terms from Google/DuckDuckGo/Bing referrer\n(function() {\n var ref = document.referrer;\n var terms = [];\n \n if (ref.includes('google.com') || ref.includes('duckduckgo.com') || ref.includes('bing.com')) {\n var url = new URL(ref);\n var q = url.searchParams.get('q') || url.searchParams.get('p');\n if (q) {\n terms = q.split(/\\s+/).filter(function(t) { return t.length > 2; });\n }\n }\n \n if (terms.length === 0) return;\n \n var style = document.createElement('style');\n style.textContent = '.userscript-highlight { background: #fbbf24; color: #1a1a2e; padding: 1px 3px; border-radius: 2px; }';\n document.head.appendChild(style);\n \n function highlight(node) {\n if (node.nodeType === 3) { // text node\n var text = node.textContent;\n var found = false;\n terms.forEach(function(term) {\n var regex = new RegExp('(' + term.replace(/[.*+?^${}()|[\\]\\\\]/g, '\\\\') + ')', 'gi');\n if (regex.test(text)) {\n found = true;\n var frag = document.createDocumentFragment();\n var parts = text.split(regex);\n parts.forEach(function(part, i) {\n if (i % 2 === 0) {\n frag.appendChild(document.createTextNode(part));\n } else {\n var span = document.createElement('span');\n span.className = 'userscript-highlight';\n span.textContent = part;\n frag.appendChild(span);\n }\n });\n node.parentNode.replaceChild(frag, node);\n }\n });\n } else if (node.nodeType === 1 && node.childNodes) { // element\n var skipTags = ['SCRIPT', 'STYLE', 'NOSCRIPT', 'TEXTAREA', 'INPUT', 'SELECT'];\n if (!skipTags.includes(node.tagName)) {\n Array.from(node.childNodes).forEach(highlight);\n }\n }\n }\n \n highlight(document.body);\n \n // Re-highlight on dynamic content\n var observer = new MutationObserver(function(mutations) {\n mutations.forEach(function(m) {\n m.addedNodes.forEach(function(node) {\n if (node.nodeType === 1 || node.nodeType === 3) highlight(node);\n });\n });\n });\n observer.observe(document.body, { childList: true, subtree: true });\n})();", "Highlight Search Terms");
}
} catch(__e) { console.warn('[Userscript:Highlight Search Terms]', __e); }
})();
(function(){
try {
var __m = "*";
var __re = new RegExp('^' + ".*" + '

              Skip to content
              Client class should throw a custom exception if the capability is unsupported #430
              Closed
              #1761
              Closed
              Client class should throw a custom exception if the capability is unsupported#430
              #1761
              Labels
              P3Nice to haves, rare edge casesenhancementRequest for a new feature that's not currently supportedgood first issueGood for newcomers - can be tackled without deep knowledge of the codebase
              Description
              @rahulkarajgikar
              rahulkarajgikar
              opened on Apr 30, 2025
              Is your feature request related to a problem? Please describe.
              
Currently, MCP Client class in https://github.com/modelcontextprotocol/typescript-sdk/blob/main/src/client/index.ts throws Error when a capability isn't supported by a server. While building any MCP client applications, this makes it hard to know, when i call client.listPrompts and get back an exception - if the exception was because of an actual failure or because the capability isn't supported
              Describe the solution you'd like
              
Client class should throw a custom exception like UnsupportedCapabilityException when the capability itself isn't supported - this makes it easy to write clients around this logic
              Describe alternatives you've considered
              
Currently i am working around this by grepping the returned exception message to see if it contains the string does not support. This is very brittle and can break easily if the exception message changes
              Metadata
              Metadata
              Assignees
              No one assigned
                Labels
                P3Nice to haves, rare edge casesenhancementRequest for a new feature that's not currently supportedgood first issueGood for newcomers - can be tackled without deep knowledge of the codebase
                Type
                No type
                Projects
                No projects
                  Milestone
                  No milestone
                  Relationships
                  None yet
                  Development
                  No branches or pull requests
                  Issue actions
                  
, 'i');
if (__m === '*' || __re.test(location.href)) {
injectUserscript("// Strip utm_, fbclid, gclid, etc. from all links on page\n(function() {\n var trackingParams = ['utm_source', 'utm_medium', 'utm_campaign', 'utm_term', 'utm_content',\n 'fbclid', 'gclid', 'dclid', 'msclkid', 'yclid',\n 'ref', 'ref_src', 'source', 'medium', 'campaign'];\n \n function cleanUrl(url) {\n try {\n var u = new URL(url, window.location.origin);\n var changed = false;\n trackingParams.forEach(function(p) {\n if (u.searchParams.has(p)) {\n u.searchParams.delete(p);\n changed = true;\n }\n });\n return changed ? u.toString() : url;\n } catch (e) {\n return url;\n }\n }\n \n function cleanLinks() {\n document.querySelectorAll('a[href]').forEach(function(a) {\n var clean = cleanUrl(a.href);\n if (clean !== a.href) a.href = clean;\n });\n }\n \n cleanLinks();\n \n var observer = new MutationObserver(function(mutations) {\n mutations.forEach(function(m) {\n m.addedNodes.forEach(function(node) {\n if (node.nodeType === 1) {\n if (node.tagName === 'A') cleanLinks();\n node.querySelectorAll('a[href]').forEach(function(a) {\n var clean = cleanUrl(a.href);\n if (clean !== a.href) a.href = clean;\n });\n }\n });\n });\n });\n observer.observe(document.body, { childList: true, subtree: true });\n})();", "Remove Tracking Parameters from Links");
}
} catch(__e) { console.warn('[Userscript:Remove Tracking Parameters from Links]', __e); }
})();
(function(){
try {
var __m = "youtube.com";
var __re = new RegExp('^' + "youtube\\.com" + '

                  Skip to content
                  Client class should throw a custom exception if the capability is unsupported #430
                  Closed
                  #1761
                  Closed
                  Client class should throw a custom exception if the capability is unsupported#430
                  #1761
                  Labels
                  P3Nice to haves, rare edge casesenhancementRequest for a new feature that's not currently supportedgood first issueGood for newcomers - can be tackled without deep knowledge of the codebase
                  Description
                  @rahulkarajgikar
                  rahulkarajgikar
                  opened on Apr 30, 2025
                  Is your feature request related to a problem? Please describe.
                  
Currently, MCP Client class in https://github.com/modelcontextprotocol/typescript-sdk/blob/main/src/client/index.ts throws Error when a capability isn't supported by a server. While building any MCP client applications, this makes it hard to know, when i call client.listPrompts and get back an exception - if the exception was because of an actual failure or because the capability isn't supported
                  Describe the solution you'd like
                  
Client class should throw a custom exception like UnsupportedCapabilityException when the capability itself isn't supported - this makes it easy to write clients around this logic
                  Describe alternatives you've considered
                  
Currently i am working around this by grepping the returned exception message to see if it contains the string does not support. This is very brittle and can break easily if the exception message changes
                  Metadata
                  Metadata
                  Assignees
                  No one assigned
                    Labels
                    P3Nice to haves, rare edge casesenhancementRequest for a new feature that's not currently supportedgood first issueGood for newcomers - can be tackled without deep knowledge of the codebase
                    Type
                    No type
                    Projects
                    No projects
                      Milestone
                      No milestone
                      Relationships
                      None yet
                      Development
                      No branches or pull requests
                      Issue actions
                      
, 'i');
if (__m === '*' || __re.test(location.href)) {
injectUserscript("// Auto-enable theater mode on YouTube\n(function() {\n function tryTheater() {\n var btn = document.querySelector('button[aria-label=\"Theater mode\"], ytd-player #player button[title=\"Theater mode\"]');\n if (btn && !btn.classList.contains('activated')) {\n btn.click();\n }\n }\n \n // Try immediately\n tryTheater();\n \n // Try after navigation (SPA)\n var lastUrl = location.href;\n setInterval(function() {\n if (location.href !== lastUrl) {\n lastUrl = location.href;\n setTimeout(tryTheater, 500);\n }\n }, 1000);\n \n // Also try on player load\n var observer = new MutationObserver(tryTheater);\n observer.observe(document.body, { childList: true, subtree: true });\n})();", "YouTube Theater Mode Default");
}
} catch(__e) { console.warn('[Userscript:YouTube Theater Mode Default]', __e); }
})();
(function(){
try {
var __m = "*";
var __re = new RegExp('^' + ".*" + '

                      Skip to content
                      Client class should throw a custom exception if the capability is unsupported #430
                      Closed
                      #1761
                      Closed
                      Client class should throw a custom exception if the capability is unsupported#430
                      #1761
                      Labels
                      P3Nice to haves, rare edge casesenhancementRequest for a new feature that's not currently supportedgood first issueGood for newcomers - can be tackled without deep knowledge of the codebase
                      Description
                      @rahulkarajgikar
                      rahulkarajgikar
                      opened on Apr 30, 2025
                      Is your feature request related to a problem? Please describe.
                      
Currently, MCP Client class in https://github.com/modelcontextprotocol/typescript-sdk/blob/main/src/client/index.ts throws Error when a capability isn't supported by a server. While building any MCP client applications, this makes it hard to know, when i call client.listPrompts and get back an exception - if the exception was because of an actual failure or because the capability isn't supported
                      Describe the solution you'd like
                      
Client class should throw a custom exception like UnsupportedCapabilityException when the capability itself isn't supported - this makes it easy to write clients around this logic
                      Describe alternatives you've considered
                      
Currently i am working around this by grepping the returned exception message to see if it contains the string does not support. This is very brittle and can break easily if the exception message changes
                      Metadata
                      Metadata
                      Assignees
                      No one assigned
                        Labels
                        P3Nice to haves, rare edge casesenhancementRequest for a new feature that's not currently supportedgood first issueGood for newcomers - can be tackled without deep knowledge of the codebase
                        Type
                        No type
                        Projects
                        No projects
                          Milestone
                          No milestone
                          Relationships
                          None yet
                          Development
                          No branches or pull requests
                          Issue actions
                          
, 'i');
if (__m === '*' || __re.test(location.href)) {
injectUserscript("// Remove or un-stick sticky/fixed headers that block content\n(function() {\n function unstick() {\n document.querySelectorAll('header, nav, [role=\"banner\"], .header, .navbar, .sticky, .fixed-top, [style*=\"position: fixed\"], [style*=\"position:sticky\"]').forEach(function(el) {\n if (el.style.position === 'fixed' || el.style.position === 'sticky' || \n getComputedStyle(el).position === 'fixed' || getComputedStyle(el).position === 'sticky') {\n el.style.position = 'static';\n el.style.top = 'auto';\n el.style.zIndex = 'auto';\n }\n });\n }\n \n unstick();\n \n var observer = new MutationObserver(unstick);\n observer.observe(document.body, { childList: true, subtree: true, attributes: true, attributeFilter: ['style', 'class'] });\n})();", "Kill Sticky Headers");
}
} catch(__e) { console.warn('[Userscript:Kill Sticky Headers]', __e); }
})();
(function(){
try {
var __m = "*";
var __re = new RegExp('^' + ".*" + '

                          Skip to content
                          Client class should throw a custom exception if the capability is unsupported #430
                          Closed
                          #1761
                          Closed
                          Client class should throw a custom exception if the capability is unsupported#430
                          #1761
                          Labels
                          P3Nice to haves, rare edge casesenhancementRequest for a new feature that's not currently supportedgood first issueGood for newcomers - can be tackled without deep knowledge of the codebase
                          Description
                          @rahulkarajgikar
                          rahulkarajgikar
                          opened on Apr 30, 2025
                          Is your feature request related to a problem? Please describe.
                          
Currently, MCP Client class in https://github.com/modelcontextprotocol/typescript-sdk/blob/main/src/client/index.ts throws Error when a capability isn't supported by a server. While building any MCP client applications, this makes it hard to know, when i call client.listPrompts and get back an exception - if the exception was because of an actual failure or because the capability isn't supported
                          Describe the solution you'd like
                          
Client class should throw a custom exception like UnsupportedCapabilityException when the capability itself isn't supported - this makes it easy to write clients around this logic
                          Describe alternatives you've considered
                          
Currently i am working around this by grepping the returned exception message to see if it contains the string does not support. This is very brittle and can break easily if the exception message changes
                          Metadata
                          Metadata
                          Assignees
                          No one assigned
                            Labels
                            P3Nice to haves, rare edge casesenhancementRequest for a new feature that's not currently supportedgood first issueGood for newcomers - can be tackled without deep knowledge of the codebase
                            Type
                            No type
                            Projects
                            No projects
                              Milestone
                              No milestone
                              Relationships
                              None yet
                              Development
                              No branches or pull requests
                              Issue actions
                              
, 'i');
if (__m === '*' || __re.test(location.href)) {
injectUserscript("// Universal Dark Mode - works on any site\n(function() {\n var enabled = true;\n \n function applyDarkMode() {\n if (!enabled) return;\n \n // Create style element if it doesn't exist\n var style = document.getElementById('universal-dark-mode-style');\n if (!style) {\n style = document.createElement('style');\n style.id = 'universal-dark-mode-style';\n document.head.appendChild(style);\n }\n \n // Dark mode CSS - inverts colors but preserves images/video\n style.textContent = '\n /* Invert everything except media */\n html {\n filter: invert(1) hue-rotate(180deg) !important;\n background: #1a1a2e !important;\n }\n \n /* Restore images, videos, iframes, canvas */\n img, video, iframe, canvas, svg, picture, [style*=\"background-image\"] {\n filter: invert(1) hue-rotate(180deg) !important;\n }\n \n /* Preserve specific elements that should not be inverted */\n .no-dark-mode, .no-dark-mode *,\n [data-theme=\"light\"], [data-theme=\"light\"],\n .ace_editor, .ace_editor *,\n .CodeMirror, .CodeMirror *,\n .monaco-editor, .monaco-editor *,\n .markdown-body pre, .markdown-body pre *,\n .highlight, .highlight *,\n pre code, pre code * {\n filter: none !important;\n }\n \n /* Fix common UI elements */\n .modal, .popup, .dropdown-menu, .tooltip, .popover {\n filter: invert(1) hue-rotate(180deg) !important;\n background: #2d2d44 !important;\n border-color: #444 !important;\n }\n \n /* Scrollbars */\n ::-webkit-scrollbar { background: #1a1a2e !important; }\n ::-webkit-scrollbar-thumb { background: #444 !important; }\n ::-webkit-scrollbar-thumb:hover { background: #555 !important; }\n \n /* Selection */\n ::selection { background: #4ecdc4 !important; color: #1a1a2e !important; }\n ::-moz-selection { background: #4ecdc4 !important; color: #1a1a2e !important; }\n ';\n }\n \n function removeDarkMode() {\n var style = document.getElementById('universal-dark-mode-style');\n if (style) style.remove();\n }\n \n // Toggle with Alt+Shift+D\n document.addEventListener('keydown', function(e) {\n if (e.altKey && e.shiftKey && e.key === 'D') {\n e.preventDefault();\n enabled = !enabled;\n if (enabled) {\n applyDarkMode();\n console.log('[Universal Dark Mode] Enabled');\n } else {\n removeDarkMode();\n console.log('[Universal Dark Mode] Disabled');\n }\n }\n });\n \n // Apply on load\n applyDarkMode();\n \n // Re-apply on dynamic content\n var observer = new MutationObserver(function(mutations) {\n if (enabled && !document.getElementById('universal-dark-mode-style')) {\n applyDarkMode();\n }\n });\n observer.observe(document.head, { childList: true });\n \n console.log('[Universal Dark Mode] Loaded - Press Alt+Shift+D to toggle');\n})();", "Universal Dark Mode");
}
} catch(__e) { console.warn('[Userscript:Universal Dark Mode]', __e); }
})();
})();

                              Skip to content
                              Client class should throw a custom exception if the capability is unsupported #430
                              Closed
                              #1761
                              Closed
                              Client class should throw a custom exception if the capability is unsupported#430
                              #1761
                              Labels
                              P3Nice to haves, rare edge casesenhancementRequest for a new feature that's not currently supportedgood first issueGood for newcomers - can be tackled without deep knowledge of the codebase
                              Description
                              @rahulkarajgikar
                              rahulkarajgikar
                              opened on Apr 30, 2025
                              Is your feature request related to a problem? Please describe.
                              
Currently, MCP Client class in https://github.com/modelcontextprotocol/typescript-sdk/blob/main/src/client/index.ts throws Error when a capability isn't supported by a server. While building any MCP client applications, this makes it hard to know, when i call client.listPrompts and get back an exception - if the exception was because of an actual failure or because the capability isn't supported
                              Describe the solution you'd like
                              
Client class should throw a custom exception like UnsupportedCapabilityException when the capability itself isn't supported - this makes it easy to write clients around this logic
                              Describe alternatives you've considered
                              
Currently i am working around this by grepping the returned exception message to see if it contains the string does not support. This is very brittle and can break easily if the exception message changes
                              Metadata
                              Metadata
                              Assignees
                              No one assigned
                                Labels
                                P3Nice to haves, rare edge casesenhancementRequest for a new feature that's not currently supportedgood first issueGood for newcomers - can be tackled without deep knowledge of the codebase
                                Type
                                No type
                                Projects
                                No projects
                                  Milestone
                                  No milestone
                                  Relationships
                                  None yet
                                  Development
                                  No branches or pull requests
                                  Issue actions