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by REX-codebase
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Python
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Go back in browser history

browser_back

Navigate back to the previous history entry in a browser session without adding a new entry. If already at the first entry, returns current status; errors preserve history index.

Instructions

Loads the previous history entry in the active or named browser session without adding a new history entry. Use it for history traversal rather than browser_navigate. If history is already at its first entry, it is a no-op that returns current page status. A navigation failure returns an error and preserves the history index; omitting session_id reuses or creates the active/default session.

Input Schema

TableJSON Schema
NameRequiredDescriptionDefault
session_idNoOptional browser tab/session identifier.

Output Schema

TableJSON Schema
NameRequiredDescriptionDefault

No arguments

Schema Changelog

Changes observed during successful MCP inspections.

  1. Changed1 schema field changedv1.3.5
    • changedOutput schema / (root)
      Previous value: -nullNew value: +{
+  "additionalProperties": true,
+  "type": "object"
+}
  2. First observedv1.3.2

TDQS

A4.9/5.0
Behavior5/5

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

Annotations are sparse, so the description carries the burden and succeeds. It discloses that the operation does not add a new history entry, becomes a no-op at the first entry, returns an error on navigation failure while preserving the history index, and reuses/creates the default session when session_id is omitted. This goes well beyond the annotations.

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?

Three dense sentences deliver all essential information with no filler. The main purpose is front-loaded, and each sentence earns its place by clarifying scope, edge behavior, and error handling.

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?

For a one-optional-parameter tool with an output schema, the description covers the necessary behavioral, error, and session semantics. Nothing an agent needs to invoke it correctly is missing.

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 coverage is 100% for the single session_id parameter, but the description adds meaningful behavior: omitting session_id reuses or creates the active/default session, and the first sentence notes 'active or named browser session.' This extra context pushes it above baseline.

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 clearly states the operation: 'Loads the previous history entry in the active or named browser session' with the key nuance 'without adding a new history entry.' It explicitly differentiates from browser_navigate, and the name plus context make the distinction from browser_forward obvious.

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 an explicit usage directive: 'Use it for history traversal rather than browser_navigate.' It also covers edge conditions (no-op at first entry), behavior on failure, and session fallback semantics, providing enough guidance for an agent to choose this tool appropriately.

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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