Railway MCP Server

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

No annotations are provided, so the description carries the full burden. It discloses that the tool can both create and update variables, mentions it's for configuration values, connection strings, and secrets, and implies it's for persistent changes (not temporary). However, it doesn't detail error conditions, rate limits, or authentication requirements, leaving some behavioral aspects unclear.

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

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

The description is well-structured with bullet points, icons, and clear sections, making it easy to scan. Every sentence adds value—no redundant information. It's front-loaded with the core purpose, followed by detailed guidance.

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

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

Given the complexity (a mutation tool with 5 parameters), no annotations, and no output schema, the description does a good job by covering purpose, usage, prerequisites, and alternatives. However, it lacks details on return values or error handling, which would be helpful for a tool with no output schema.

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

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

Schema description coverage is 100%, so the schema already documents all parameters. The description doesn't add any parameter-specific details beyond what's in the schema, such as explaining the relationship between serviceId and shared variables. Baseline 3 is appropriate when the schema provides complete parameter documentation.

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

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

The description clearly states the specific action ('Create or update an environment variable') and resource ('environment variable'), distinguishing it from sibling tools like variable_bulk_set, variable_list, and variable_delete. The title is null, so the description fully defines the purpose.

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

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

The description provides explicit guidance with 'Best for' and 'Not for' sections, names a specific alternative (variable_bulk_set), lists prerequisites (service_list), and suggests next steps (deployment_trigger, service_restart). This comprehensively covers when to use and avoid this tool.

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