{"passport":{"unfragile":{"@version":"1.0","version":"2026-05","artifact":{"id":"awesome-mcp-expr-lang","slug":"mcp-expr-lang","name":"MCP Expr Lang","type":"mcp","url":"https://github.com/ivan-saorin/mcp-expr-lang","page_url":"https://unfragile.ai/mcp-expr-lang","categories":["mcp-servers"],"tags":[],"pricing":{"model":"open_source","free":true,"starting_price":null},"status":"active","verified":false},"capabilities":[{"id":"awesome-mcp-expr-lang__cap_0","uri":"capability://tool.use.integration.expression.evaluation.via.mcp.protocol.bridge","name":"expression evaluation via mcp protocol bridge","description":"Bridges Claude AI with the expr-lang expression evaluation engine through the Model Context Protocol (MCP), enabling Claude to execute arbitrary expressions and receive computed results. The integration translates Claude's tool-calling requests into expr-lang AST evaluation, marshaling results back through MCP's standardized resource/tool interface. This allows Claude to perform dynamic computation without embedding a full runtime in the LLM context.","intents":["Execute mathematical and logical expressions from Claude conversations without hardcoding formulas","Enable Claude to dynamically compute values during multi-turn reasoning tasks","Integrate expr-lang's expression syntax into Claude-powered agents for real-time evaluation"],"best_for":["AI engineers building Claude agents that need dynamic expression evaluation","Teams integrating expr-lang into LLM-powered workflows without custom API layers","Developers prototyping expression-based automation with Claude as the orchestrator"],"limitations":["Evaluation latency depends on MCP server round-trip time — typically 50-200ms per expression","No built-in expression caching or memoization across multiple identical evaluations","Limited to expr-lang's expression syntax — cannot execute arbitrary code or system commands","Requires MCP-compatible Claude client (Claude Desktop, or custom MCP host) — not available in web chat"],"requires":["Claude Desktop or MCP-compatible Claude client","Node.js 16+ (for running the MCP server)","expr-lang library (included as dependency)","MCP protocol support in your Claude integration"],"input_types":["expression strings (e.g., '2 + 2 * 3')","variable bindings as JSON objects","function definitions in expr-lang syntax"],"output_types":["computed scalar values (numbers, strings, booleans)","structured evaluation results with metadata","error messages with expression parsing details"],"categories":["tool-use-integration","planning-reasoning"],"confidence":0.5,"matches":0,"success_rate":0},{"id":"awesome-mcp-expr-lang__cap_1","uri":"capability://memory.knowledge.variable.context.management.for.expression.evaluation","name":"variable context management for expression evaluation","description":"Manages stateful variable bindings and context across multiple expression evaluations within a Claude conversation. The MCP server maintains a session-scoped variable store that Claude can populate, update, and reference in subsequent expressions, enabling multi-step computations where intermediate results feed into later expressions. Variables are scoped to the MCP session and cleared on server restart.","intents":["Store intermediate computation results and reuse them in follow-up expressions","Build multi-step calculation workflows where Claude orchestrates variable assignments","Maintain state across a conversation without requiring Claude to track values in its context window"],"best_for":["Multi-turn Claude conversations involving sequential calculations","Agents performing iterative refinement of computed values","Workflows where Claude needs to reference previously computed results without re-computing"],"limitations":["Variable context is session-scoped and lost on MCP server restart — no persistence layer","No built-in variable versioning or rollback — overwrites are permanent within the session","Variable names must be valid identifiers in expr-lang — special characters or spaces require escaping","No access control or isolation between concurrent Claude conversations using the same MCP server instance"],"requires":["MCP server instance running with variable store support","Claude client capable of issuing sequential tool calls","expr-lang variable syntax knowledge"],"input_types":["variable name (string identifier)","variable value (any expr-lang-compatible type)","expression strings referencing stored variables"],"output_types":["confirmation of variable assignment","current variable value on retrieval","evaluation results incorporating variable references"],"categories":["memory-knowledge","tool-use-integration"],"confidence":0.5,"matches":0,"success_rate":0},{"id":"awesome-mcp-expr-lang__cap_2","uri":"capability://tool.use.integration.function.definition.and.invocation.in.expressions","name":"function definition and invocation in expressions","description":"Enables Claude to define custom functions within expr-lang's expression syntax and invoke them across multiple evaluations. Functions are registered in the MCP server's function registry and can reference variables, accept parameters, and return computed values. This allows Claude to abstract repeated computation patterns into reusable functions without modifying the MCP server code.","intents":["Define reusable computation patterns (e.g., tax calculation, unit conversion) that Claude can invoke multiple times","Abstract complex multi-step expressions into named functions for clarity and maintainability","Enable Claude to create domain-specific expression libraries on-the-fly for specialized workflows"],"best_for":["Agents performing repeated calculations with variations (e.g., pricing models with different parameters)","Workflows where Claude needs to define domain-specific helpers without server-side code changes","Multi-turn conversations where function definitions are reused across many expression evaluations"],"limitations":["Function definitions are session-scoped and lost on MCP server restart","No built-in function versioning or overload resolution — redefining a function overwrites the previous definition","Limited to expr-lang's function syntax — cannot define recursive functions or functions with side effects","Function parameter validation is minimal — type mismatches may cause runtime errors during evaluation"],"requires":["Understanding of expr-lang function definition syntax","MCP server with function registry support","Claude client capable of issuing function definition and invocation tool calls"],"input_types":["function name (string identifier)","parameter list (comma-separated identifiers)","function body (expr-lang expression string)","function invocation arguments (values or expressions)"],"output_types":["confirmation of function registration","function invocation results (computed values)","error messages for syntax or parameter mismatches"],"categories":["tool-use-integration","planning-reasoning"],"confidence":0.5,"matches":0,"success_rate":0},{"id":"awesome-mcp-expr-lang__cap_3","uri":"capability://safety.moderation.type.aware.expression.parsing.and.validation","name":"type-aware expression parsing and validation","description":"Parses and validates expressions against expr-lang's type system before evaluation, providing Claude with early feedback on syntax errors, type mismatches, and undefined variable references. The parser uses expr-lang's AST construction to detect issues without executing the expression, enabling Claude to refine expressions iteratively. Validation results include detailed error messages with line/column information.","intents":["Validate expression syntax before execution to catch errors early in the conversation","Provide Claude with detailed error feedback to guide expression refinement","Ensure type safety by detecting type mismatches before evaluation"],"best_for":["Interactive Claude conversations where users want immediate feedback on expression validity","Agents that need to validate user-provided expressions before passing them to expr-lang","Workflows where catching syntax errors early reduces iteration cycles"],"limitations":["Validation is static and cannot detect all runtime errors (e.g., division by zero)","Error messages depend on expr-lang's parser quality — some errors may be cryptic","No type inference — expressions with implicit type conversions may validate but fail at runtime","Validation latency is negligible for simple expressions but grows with expression complexity"],"requires":["expr-lang parser library (included in MCP server)","MCP tool for validation requests","Claude client capable of issuing validation tool calls"],"input_types":["expression string","optional variable type hints (for context)","optional function signature hints"],"output_types":["validation success/failure status","detailed error messages with location info","inferred type information (if available)"],"categories":["safety-moderation","tool-use-integration"],"confidence":0.5,"matches":0,"success_rate":0},{"id":"awesome-mcp-expr-lang__cap_4","uri":"capability://data.processing.analysis.multi.expression.batch.evaluation.with.result.aggregation","name":"multi-expression batch evaluation with result aggregation","description":"Processes multiple expressions in a single MCP call and returns aggregated results, reducing round-trip latency for workflows that need to evaluate many expressions. The batch evaluator executes expressions sequentially (or in parallel if supported by the backend) and collects results with per-expression error handling, allowing Claude to retrieve multiple computed values in one request. Results are returned as a structured array with metadata about each evaluation.","intents":["Evaluate multiple expressions in parallel to reduce latency in multi-step workflows","Retrieve results for a set of related calculations in a single MCP call","Aggregate results from multiple expressions for downstream processing or reporting"],"best_for":["Agents performing batch calculations (e.g., pricing multiple items, computing multiple metrics)","Workflows where latency is critical and reducing MCP round-trips is important","Scenarios where Claude needs to evaluate many expressions without blocking on individual results"],"limitations":["Batch evaluation order is deterministic but not parallelized in most implementations — latency is sum of individual evaluations","Error in one expression does not halt batch processing but is reported per-expression — partial failures are possible","Batch size limits may apply depending on MCP server configuration — very large batches may timeout","Results are not cached across batches — identical expressions in different batches are re-evaluated"],"requires":["MCP server with batch evaluation support","Claude client capable of issuing batch tool calls","expr-lang expressions (multiple, as array or list)"],"input_types":["array of expression strings","optional shared variable context","optional evaluation options (timeout, precision, etc.)"],"output_types":["array of evaluation results (one per expression)","per-expression status (success/failure)","error details for failed expressions","execution metadata (timing, resource usage)"],"categories":["data-processing-analysis","tool-use-integration"],"confidence":0.5,"matches":0,"success_rate":0},{"id":"awesome-mcp-expr-lang__cap_5","uri":"capability://data.processing.analysis.expression.result.formatting.and.serialization","name":"expression result formatting and serialization","description":"Converts expr-lang evaluation results into multiple output formats (JSON, CSV, plain text, formatted tables) for integration with downstream tools and Claude's output capabilities. The formatter handles type conversion, null/undefined handling, and precision control for numeric results. This enables Claude to present computed values in formats suitable for different contexts (e.g., JSON for APIs, tables for reports).","intents":["Format expression results as JSON for integration with other tools and APIs","Generate human-readable tables or reports from computed values","Export results in CSV format for spreadsheet or data analysis tools"],"best_for":["Agents that need to present computed results in multiple formats","Workflows integrating expr-lang results with downstream tools (APIs, databases, spreadsheets)","Scenarios where Claude needs to generate reports or structured output from expressions"],"limitations":["Formatting options are limited to built-in formats — custom formatters require server-side code changes","Precision control for floats may lose information — rounding behavior is format-dependent","Large result sets may produce unwieldy output — no built-in pagination or truncation","Nested or complex types may not format cleanly in all output formats (e.g., CSV with nested objects)"],"requires":["MCP server with formatting support","expr-lang evaluation results","Target output format specification"],"input_types":["expression evaluation result (any expr-lang type)","target format (json, csv, text, table, etc.)","optional formatting options (precision, delimiter, headers, etc.)"],"output_types":["formatted string (JSON, CSV, plain text, or table)","metadata about formatting (rows, columns, precision used)"],"categories":["data-processing-analysis","text-generation-language"],"confidence":0.5,"matches":0,"success_rate":0}],"trust":{"score":28,"verified":false,"data_access_risk":"moderate","permissions":["Claude Desktop or MCP-compatible Claude client","Node.js 16+ (for running the MCP server)","expr-lang library (included as dependency)","MCP protocol support in your Claude integration","MCP server instance running with variable store support","Claude client capable of issuing sequential tool calls","expr-lang variable syntax knowledge","Understanding of expr-lang function definition syntax","MCP server with function registry support","Claude client capable of issuing function definition and invocation tool calls"],"failure_modes":["Evaluation latency depends on MCP server round-trip time — typically 50-200ms per expression","No built-in expression caching or memoization across multiple identical evaluations","Limited to expr-lang's expression syntax — cannot execute arbitrary code or system commands","Requires MCP-compatible Claude client (Claude Desktop, or custom MCP host) — not available in web chat","Variable context is session-scoped and lost on MCP server restart — no persistence layer","No built-in variable versioning or rollback — overwrites are permanent within the session","Variable names must be valid identifiers in expr-lang — special characters or spaces require escaping","No access control or isolation between concurrent Claude conversations using the same MCP server instance","Function definitions are session-scoped and lost on MCP server restart","No built-in function versioning or overload resolution — redefining a function overwrites the previous definition","builder identity is not verified yet","no observed match outcomes yet"],"rank_breakdown":{"adoption":0.05,"quality":0.37,"ecosystem":0.39999999999999997,"match_graph":0.25,"freshness":0.52,"weights":{"adoption":0.25,"quality":0.25,"ecosystem":0.15,"match_graph":0.23,"freshness":0.12}},"observed_outcomes":{"matches":0,"success_rate":0,"avg_confidence":0,"top_intents":[],"last_matched_at":null},"maintenance":{"status":"active","updated_at":"2026-06-17T09:51:03.578Z","last_scraped_at":"2026-05-03T14:00:15.503Z","last_commit":null},"community":{"stars":null,"forks":null,"weekly_downloads":null,"model_downloads":null,"model_likes":null}},"distribution":{"claim_url":"https://unfragile.ai/submit?claim=mcp-expr-lang","compare_url":"https://unfragile.ai/compare?artifact=mcp-expr-lang"}},"signature":"qSMox5Kh38SbPuYra1CLe3dTSUB49QGN8qMFzfQ/coa+I8k4tHFspL/PLBSQSa+ZutLOojtpgzbQ736YIRQkAA==","signedAt":"2026-06-22T15:19:18.152Z","signedBy":"unfragile.ai","version":1},"_links":{"self":"https://unfragile.ai/api/v1/passport/mcp-expr-lang","artifact":"https://unfragile.ai/mcp-expr-lang","verify":"https://unfragile.ai/api/v1/verify?slug=mcp-expr-lang","publicKey":"https://unfragile.ai/api/v1/trust-passport-public-key","spec":"https://unfragile.ai/trust","schema":"https://unfragile.ai/schema.json","docs":"https://unfragile.ai/docs"}}