updateVarChange a stored environment variable or credential to a new value, specifying environment, region, and secret status for a specific app and workspace.
Update an environment variable or credential value
| Name | Required | Description | Default |
|---|---|---|---|
| env | No | ||
| varId | Yes | ||
| region | No | ||
| appSlug | Yes | ||
| requestBody | No | The JSON request body. | |
| workspaceSlug | Yes |
Changes observed during successful MCP inspections.
v0.5.1Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
Annotations already declare readOnlyHint=false, openWorldHint=true, and destructiveHint=true, so the agent knows this is a mutating operation with potential side effects. The description adds minimal context beyond the word 'update' and does not describe permission requirements, reversibility, or the effect on running applications. It does not contradict annotations, so a neutral score of 3 is appropriate given the annotation coverage.
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 a single, front-loaded sentence with no fluff, which is efficient. However, it is so minimal that it lacks substance needed for effective agent guidance. It earns a middle score because it is concise but not adequately informative.
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?
For a mutation tool with six parameters, a nested request body, no output schema, and destructive annotations, this description is severely lacking. It does not explain the request body structure, the meaning of env/region, or the consequences of updating a secret. An agent cannot correctly invoke this tool without additional external knowledge.
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 only 17% (only the requestBody property has a description). The description provides no explanation for parameters like env, region, varId, or the isSecret field. It fails to compensate for the low coverage, leaving most parameters semantically undocumented.
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 action (update) and the resource (environment variable or credential value). It is specific enough to differentiate from createVar and deleteVar, though it does not explicitly name alternatives. The verb and resource are clear and unambiguous.
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?
No guidance is given on when to use this tool versus alternatives like createVar or deleteVar. It does not mention prerequisites such as the variable already existing (varId required) or when updating is appropriate (e.g., changing a secret vs. a non-secret). The description implies usage but provides no explicit context or exclusions.
Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.