Horizon MCP Server

horizon_refresh_token

Exchange a refresh token for a new access token when manual renewal is required, as the server typically refreshes tokens automatically.

Instructions

Exchange the refresh token for a new access token.

Rarely needed: the server already refreshes an expired access token automatically.

Input Schema

TableJSON Schema

Name	Required	Description	Default
`base_url`	No	Horizon server URL. Defaults to HORIZON_BASE_URL env var.
`refresh_token`	No	Refresh token to use. Omit to use the one the server stored at login (normally what you want).

Output Schema

TableJSON Schema

Name	Required	Description	Default
No arguments

Schema Changelog

Changes observed during successful MCP inspections.

Changed7 schema fields changedv0.2.0Sep 30, 2026

addedInput schema / properties / refresh_token / anyOf

Added value: +[
+  {
+    "format": "password",
+    "type": "string",
+    "writeOnly": true
+  },
+  {
+    "type": "null"
+  }
+]

addedInput schema / properties / refresh_token / default
```
Added value: +null
```

changedInput schema / properties / refresh_token / description

Previous value: -"Refresh token obtained from horizon_login"New value: +"Refresh token to use. Omit to use the one the server stored at login (normally what you want)."

removedInput schema / properties / refresh_token / format
```
Removed value: -"password"
```
removedInput schema / properties / refresh_token / type
```
Removed value: -"string"
```
removedInput schema / properties / refresh_token / writeOnly
```
Removed value: -true
```
removedInput schema / required
```
Removed value: -[
-  "refresh_token"
-]
```

First observedv0.1.0Sep 10, 2026

TDQS

A4/5.0

Behavior3/5

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

Annotations already declare non-read-only, non-idempotent, non-destructive, closed-world. The description adds that automatic refresh normally supersedes this call, which is useful behavior context, but omits whether the stored refresh token is rotated/invalidated and what happens on an invalid token.

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

Conciseness5/5

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

Two short sentences, zero waste, with the primary action stated first and the caveat immediately after. Nothing to trim.

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

Completeness4/5

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

With an output schema present and fully documented optional parameters, the description need not explain return values. It covers the main practical concern (when it's needed at all); only edge-case failure behavior is unaddressed, which is minor here.

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

Parameters3/5

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

Schema description coverage is 100% and both parameters (base_url, refresh_token) are documented in the schema, including the 'omit to use the stored token' default. The description adds no parameter-level meaning beyond that, so the baseline 3 applies.

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

Purpose4/5

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

The description states a specific verb (exchange) and resource (refresh token for access token), so the operation is unambiguous. It does not explicitly differentiate itself from horizon_login/horizon_logout, but the token-exchange semantics are distinct enough on their own.

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?

It gives explicit when-not guidance: 'Rarely needed: the server already refreshes an expired access token automatically.' That tells the agent the default path is automatic refresh and this tool is the exception, which is exactly the routing information needed.

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

Deploy Server