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efranceschetti

festo-codesys-mcp

ST Symbols (cross-file outline & definition)

st_symbols
Read-onlyIdempotent

Index CODESYS .st files and navigate symbols across files. Use to outline top-level symbols or resolve a name to its definition.

Instructions

Index a directory of .st files and navigate symbols across files — dialect-aware (CODESYS V3.5), comment/string-safe, better than grep. USE WHEN: you need to navigate an existing .st project — outline symbols or resolve a definition across files (better than grep). Actions: 'outline' — project map. Returns top-level symbols (functionBlock/program/function/enum/struct/gvl) by default; pass kindFilter to include vars/members (e.g. ["inputVar","globalVar"]). 'definition' — resolve a name (case-insensitive) to its definition(s); requires 'name'. Notes: sourceDir must be inside the workspace unless FESTO_MCP_ALLOW_OUTSIDE_WORKSPACE=1. Line numbers and find-references arrive in a later version (this version returns file + container).

Input Schema

TableJSON Schema
NameRequiredDescriptionDefault
nameNoSymbol name (required for action=definition)
actionYes'outline' = project map | 'definition' = resolve a name
sourceDirYesDirectory containing .st files (recursive scan)
kindFilterNoFilter by SymbolKind (e.g. ["functionBlock","globalVar"])

Output Schema

TableJSON Schema
NameRequiredDescriptionDefault
actionYes
symbolsYes
fileCountYes
sourceDirYes
symbolCountYes
Behavior5/5

Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?

Annotations already declare readOnly, idempotent, non-destructive. The description adds valuable behavioral context: dialect-aware (CODESYS V3.5), comment/string-safe, workspace restriction with env var override, and return format (file + container). No contradictions.

Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.

Conciseness4/5

Is the description appropriately sized, front-loaded, and free of redundancy?

The description is well-structured with sections, bullet points, and clear language. It is somewhat lengthy but every sentence adds value. Could be slightly more concise, but overall efficient for the information provided.

Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.

Completeness5/5

Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?

Given the presence of an output schema, the description appropriately focuses on usage and constraints. It covers workspace restrictions, different actions, and explicitly mentions limitations (no line numbers/find-references). The description is complete for an agent to use the tool correctly.

Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.

Parameters4/5

Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?

Schema description coverage is 100%, so each parameter is documented. The description adds actionable nuance: explains default behavior of outline (top-level symbols) and how kindFilter extends it, and notes that definition is case-insensitive. This adds value beyond the schema.

Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.

Purpose5/5

Does the description clearly state what the tool does and how it differs from similar tools?

The description uses specific verbs ('index', 'navigate') and clearly distinguishes the tool from siblings by noting it is dialect-aware and better than grep. It explicitly mentions the two actions and the resource (.st files).

Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.

Usage Guidelines5/5

Does the description explain when to use this tool, when not to, or what alternatives exist?

The description provides explicit 'USE WHEN' guidance: to navigate an existing .st project for outlining or resolving definitions. It also clarifies what the tool does NOT do (line numbers, find-references), directing agents to future updates or other tools.

Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.

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