Model Context Protocol (MCP)

Kolo comes with an MCP server, which can be used to provide relevant trace data to your IDE or AI agent.

Using Kolo as an MCP server

To start the Kolo MCP server, you need to run the following command:

kolo mcp

Kolo’s MCP server essentially wraps a number of commands in the Kolo CLI and adds some additional description to help LLMs understand when to invoke the tools.

MCP tools available in kolo:

• list_traces

• get_pinned_traces

• get_recent_compact_traces

• get_compact_trace

• get_trace_node

list_traces

Equivalent to kolo trace list

Tool description

Concisely list available traces, ordered by most recent first.

This is useful for getting an overview of what traces are available and
finding specific traces you might want to analyze further.
It's also useful to see recent activity. Traces may be named.
Call this tool *often* to orient yourself and see where useful context may lie.
After using this tool, call get_compact_trace to get more details about a specific trace.

Args:
    count: How many traces to list (default: 30)

Example:
    >>> list_traces(5)
    [
        "200 POST /buttons/poll_action/ (20h ago,   1.3 MB, trc_01JPMVDD0TRMW30JDAWR8HR4ZR)",
        "200 POST /poll/command/poll/ (20h ago, 321.1 KB, trc_01JPMVDAE8TA7N06JHJ809K2PE)",
        "200 POST /buttons/poll_action/vote/ (21h ago, 384.9 KB, trc_01JPMPK97J568NH2JZP5J2P02F)",
        "trc_01JPMKX2BEYZT7VM8A3FWC6DVK (22h ago, 346.8 KB)",
        "trc_01JPMKTVE3X7WRRE06Y2BDWXZ5 (22h ago, 346.8 KB)"
    ]

get_pinned_traces

Equivalent to kolo trace compact --pinned

Tool description

Get compact representations of all pinned traces.

This is useful for understanding the key execution paths that have been marked
as important. Pinned traces often represent core functionality or critical
paths through the codebase.

Args:
    include_returns: Whether to include return values (warning: can be verbose)

Example:
    >>> get_pinned_traces()
    [
        "main() -> process_data() -> ...",
        "test() -> validate() -> ..."
    ]

get_recent_compact_traces

Equivalent to kolo trace compact --recent

Tool description

Get the compact representation of the most recent traces.

The traces are detailed call graphs of program execution. It's as if a debugger was active
for the last 5 requests/program executions and every function call and return was logged.
It includes extremely useful data about program execution flow, function arguments, return
values, sql queries, and more.

Use this tool to get unstuck and to understand how the just executed code actually behaved
in practice. Use it to check assumptions or to answer the question "why" something didn't work.

This tool call is cheap and fast, when in doubt, make it to gather extra info.

Examples:
- A 500 error happened. The kolo trace includes the full stack trace revealing why the error happened
- Everything seems fine, but the user is reporting unexpected behaviour. The kolo trace reveals a codepath you
didn't expect and need to account for.
- You're debugging a complex issue and need to understand the flow of the program. The kolo trace shows you

Warning: Setting include_returns=True with a large count can return a lot of data.

Args:
    count: Number of recent traces to get (default: 5)
    include_returns: Whether to include return values (warning: can be verbose)

Example:
    >>> get_recent_compact_traces(2)
    [
        "main() -> process_data() -> ...",
        "test() -> validate() -> ..."
    ]

get_compact_trace

Equivalent to kolo trace compact TRACE_ID

Tool description

Get a compact representation of a specific trace.

This is useful when you need to understand what happened in a specific trace,
identified by its trace_id. The compact representation shows the sequence of
function calls and their outcomes.

Args:
    trace_id: ID of the trace to get
    include_returns: Whether to include return values (warning: can be verbose)

Example:
    >>> get_compact_trace("trc_1234567890")
    "main() -> process_data() -> validate_input() -> ..."

get_trace_node

Equivalent to kolo trace node TRACE_ID NODE_INDEX

Tool description

Get detailed information about a specific node in a trace.

This is useful when you need to deeply understand what happened at a specific
point in the execution, like examining function arguments, local variables,
or the exact line of code being executed.

Args:
    trace_id: ID of the trace containing the node
    node_index: Index of the node in the trace tree

Example:
    >>> get_trace_node("trc_123", 5)
    {"type": "call", "function": "validate_input", "args": {"data": {...}}, ...}

Troubleshooting the Kolo MCP Server

Kolo’s MCP tools not showing up. Inspect the mcp server output directly with the official mcp inspector.

npx @modelcontextprotocol/inspector kolo mcp

In some cases, you may need to explicitly set the KOLO_PATH so that kolo knows where to find your .kolo/ directory and the associated trace data. In that case, start the mcp server with:

KOLO_PATH=/path/to/your/kolo/directory kolo mcp