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 effectively discloses key behavioral traits: it's a mutation tool ('create or update'), implies persistence (not for temporary changes), and hints at scope (shared vs. service-specific variables via optional serviceId). However, it doesn't mention potential side effects like service restarts or rate limits, leaving some behavioral aspects uncovered.

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 and appropriately sized, using bullet points and icons for clarity. Every sentence earns its place by providing actionable information (purpose, best uses, exclusions, prerequisites, alternatives, next steps, related tools) without redundancy or fluff.

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 tool's complexity (mutation with 5 parameters) and lack of annotations/output schema, the description does an excellent job covering purpose, usage, and context. It mentions prerequisites, alternatives, and related tools, which helps the agent understand the ecosystem. The only minor gap is the lack of explicit output information, but this is mitigated by the clear action-oriented description.

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 5 parameters thoroughly. The description adds no additional parameter semantics beyond what's in the schema (e.g., it doesn't explain format constraints or provide examples). With high schema coverage, the baseline score of 3 is appropriate as the description doesn't compensate but doesn't detract either.

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 tool's purpose with specific verbs ('create or update') and resource ('environment variable'), and distinguishes it from sibling tools by explicitly mentioning what it's not for (bulk updates, temporary changes). The title is null, but the description fully compensates with precise action and scope.

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 on when to use this tool ('Best for: Setting configuration values, Updating connection strings, Managing service secrets'), when not to use it ('Not for: Bulk variable updates, Temporary configuration changes'), and names alternatives ('variable_bulk_set'). It also lists prerequisites ('service_list') and related tools, making usage context very clear.

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