Add --log-for human|machine flag for LLM/agent-friendly output #1508

Copilot · 2026-01-19T11:54:47Z

Current console output uses ANSI codes, Unicode box characters, and terse labels that waste tokens and are hard for LLMs/agents to parse programmatically.

Changes

New LogFor enum (Human | Machine) in DevProxy.Abstractions
--log-for CLI option as a global/recursive option with validation
logFor config property in devproxyrc.json (CLI takes precedence)
MachineConsoleFormatter outputs JSON Lines with:
- Semantic types (request, response, warning, error, mock, chaos)
- Correlation IDs (requestId)
- ISO 8601 timestamps
- Full context (URL, method, plugin)
- No buffering (streams immediately)
Schema update for logFor in rc.schema.json

Usage

devproxy --log-for machine

{"logFor": "machine"}

Output

{"type":"log","level":"info","message":"Dev Proxy listening on 127.0.0.1:8000...","category":"ProxyEngine","timestamp":"2026-01-19T12:05:44.766Z"}
{"type":"request","method":"GET","url":"https://api.example.com/users","requestId":"1","timestamp":"2026-01-19T10:30:00.000Z"}
{"type":"chaos","plugin":"RateLimitingPlugin","message":"TooManyRequests","requestId":"1","timestamp":"2026-01-19T10:30:00.050Z"}

Warning

Firewall rules blocked me from connecting to one or more addresses (expand for details)

I tried to connect to the following addresses, but was blocked by firewall rules:

aka.ms
- Triggering command: /home/REDACTED/work/dev-proxy/dev-proxy/DevProxy/bin/Debug/net10.0/devproxy /home/REDACTED/work/dev-proxy/dev-proxy/DevProxy/bin/Debug/net10.0/devproxy --help (dns block)
- Triggering command: /home/REDACTED/work/dev-proxy/dev-proxy/DevProxy/bin/Debug/net10.0/devproxy /home/REDACTED/work/dev-proxy/dev-proxy/DevProxy/bin/Debug/net10.0/devproxy --log-for machine --log-level information --no-first-run nsion (dns block)
- Triggering command: /home/REDACTED/work/dev-proxy/dev-proxy/DevProxy/bin/Debug/net10.0/devproxy /home/REDACTED/work/dev-proxy/dev-proxy/DevProxy/bin/Debug/net10.0/devproxy --log-for human --log-level information --no-first-run (dns block)

If you need me to access, download, or install something from one of these locations, you can either:

Configure Actions setup steps to set up my environment, which run before the firewall is enabled
Add the appropriate URLs or hosts to the custom allowlist in this repository's Copilot coding agent settings (admins only)

Original prompt

This section details on the original issue you should resolve

<issue_title>Add --log-for human|machine flag for LLM/agent-friendly output</issue_title>
<issue_description>## Summary

Add a new CLI flag --log-for human|machine to make Dev Proxy output consumable by coding agents and LLMs.

Problem

The current console output is optimized for human readability but creates problems when consumed by LLMs/coding agents:

Problem Description

ANSI escape codes Color codes like \x1B[31m pollute text and waste tokens

Unicode box characters ╭ ╰ │ are visual, not semantic — hard to parse programmatically

No structured output Console is human-readable prose; LLMs need JSON to reliably extract fields

Buffered output Messages held until request completes; agents cannot react in real-time

Terse/informal labels oops, skip, proc are cute but ambiguous for machines

Missing context Logs like "URL not matched" lack the actual URL

No correlation IDs Hard to trace request→response chains

Timestamps hidden Filtered by default; agents cannot measure timing

Example of current output
 req   ╭ GET https://api.example.com/users
 oops  │ 429 TooManyRequests
 warn  │ Exceeded resource limit when calling https://api.example.com/users
       ╰ 
What an agent needs
{"type":"request","method":"GET","url":"https://api.example.com/users","requestId":"1","timestamp":"2026-01-19T10:30:00.000Z"}
{"type":"chaos","plugin":"RateLimitingPlugin","status":429,"message":"TooManyRequests","requestId":"1","timestamp":"2026-01-19T10:30:00.050Z"}
{"type":"warning","plugin":"RateLimitingPlugin","message":"Exceeded resource limit","url":"https://api.example.com/users","requestId":"1","timestamp":"2026-01-19T10:30:00.051Z"}
Proposed solution

Add a new flag:
devproxy --log-for human   # Current behavior (default)
devproxy --log-for machine # Structured JSON Lines output
Why --log-for instead of --output json or --format json?

We evaluated common CLI conventions:

Tool Flag

kubectl -o, --output json|yaml|wide

Azure CLI -o, --output json|table|tsv

GitHub CLI --json

However, for LLM consumption, audience-centric naming is more intuitive than format-centric:

Aspect --log-format json --log-for machine

Semantics Describes the how Describes the who

LLM intuition "Output in JSON format" "This output is meant for me"

Discoverability Need to know JSON is the right format Obvious: "I am a machine, I use machine"

Future-proof Locked to specific format Can evolve what "machine" means internally

An LLM reading --help naturally self-identifies with --log-for machine.

Machine output requirements

When --log-for machine is set:

JSON Lines format — one JSON object per line (streamable)

No ANSI codes — strip all color/formatting escape sequences

No Unicode decorations — no box-drawing characters

Include correlation IDs — requestId in every log entry

Include timestamps — ISO 8601 format

Full context — URL, method, plugin name in each entry

Semantic message types — request, response, warning, error, mock, chaos (not oops, skip)

Configuration

Also support in devproxyrc.json:
{
  "logFor": "machine"
}
Related

Reporters (JsonReporter, PlainTextReporter) handle file output after recording

This flag handles real-time console/stdout output
</issue_description>

<agent_instructions>The --log-for arg is a global arg that can be used with any command.</agent_instructions>

Comments on the Issue (you are @copilot in this section)
@garrytrinder Great idea! The current output generates a lot of noise for LLMs so this will make the output more concise and parsable by an LLM.

Fixes Add --log-for human|machine flag for LLM/agent-friendly output #1507

💡 You can make Copilot smarter by setting up custom instructions, customizing its development environment and configuring Model Context Protocol (MCP) servers. Learn more Copilot coding agent tips in the docs.

Co-authored-by: waldekmastykarz <11164679+waldekmastykarz@users.noreply.github.com>

…y else Co-authored-by: waldekmastykarz <11164679+waldekmastykarz@users.noreply.github.com>

waldekmastykarz · 2026-01-20T09:56:10Z

@copilot update the branch with rebase and resolve conflicts ensuring all functionality is intact

Copilot · 2026-01-20T09:59:27Z

@copilot update the branch with rebase and resolve conflicts ensuring all functionality is intact

I'm unable to perform a rebase as my environment doesn't support force push operations required for rebase. However, I've verified the branch has been merged with main (commit 1859143), the build succeeds, and all --log-for functionality works correctly (tested both human and machine modes). If you'd like to rebase this branch to clean up the commit history, that would need to be done manually.

Warning

Firewall rules blocked me from connecting to one or more addresses (expand for details)

I tried to connect to the following addresses, but was blocked by firewall rules:

aka.ms
- Triggering command: /home/REDACTED/work/dev-proxy/dev-proxy/DevProxy/bin/Debug/net10.0/devproxy /home/REDACTED/work/dev-proxy/dev-proxy/DevProxy/bin/Debug/net10.0/devproxy --help (dns block)
- Triggering command: /home/REDACTED/work/dev-proxy/dev-proxy/DevProxy/bin/Debug/net10.0/devproxy /home/REDACTED/work/dev-proxy/dev-proxy/DevProxy/bin/Debug/net10.0/devproxy --log-for machine --log-level information --no-first-run (dns block)
- Triggering command: /home/REDACTED/work/dev-proxy/dev-proxy/DevProxy/bin/Debug/net10.0/devproxy /home/REDACTED/work/dev-proxy/dev-proxy/DevProxy/bin/Debug/net10.0/devproxy --log-for human --log-level information --no-first-run (dns block)

If you need me to access, download, or install something from one of these locations, you can either:

Configure Actions setup steps to set up my environment, which run before the firewall is enabled
Add the appropriate URLs or hosts to the custom allowlist in this repository's Copilot coding agent settings (admins only)

Copilot

Pull request overview

This pull request adds a --log-for flag to enable machine-readable JSON Lines output for LLMs and coding agents, addressing the challenge of parsing ANSI-decorated, human-friendly console output.

Changes:

Added LogFor enum (Human|Machine) in abstractions with EnumMember attributes for JSON serialization
Implemented MachineConsoleFormatter that outputs structured JSON Lines with semantic types, correlation IDs, and ISO 8601 timestamps
Added CLI option --log-for and configuration property logFor with validation

Reviewed changes

Copilot reviewed 8 out of 8 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
schemas/v2.1.0/rc.schema.json	Adds logFor property with human/machine enum values to the configuration schema
DevProxy/Proxy/ProxyConfiguration.cs	Adds LogFor property with JSON converter to configuration class
DevProxy/Logging/ProxyConsoleFormatterOptions.cs	Adds LogFor property to formatter options
DevProxy/Logging/MachineConsoleFormatter.cs	New formatter that outputs JSON Lines format with semantic message types and full context
DevProxy/Extensions/ILoggingBuilderExtensions.cs	Updates logging configuration to select formatter based on LogFor setting
DevProxy/Commands/DevProxyConfigOptions.cs	Adds LogFor option parsing with custom parser and validation
DevProxy/Commands/DevProxyCommand.cs	Registers --log-for as a global recursive CLI option with enum validation
DevProxy.Abstractions/Proxy/IProxyConfiguration.cs	Adds LogFor enum definition and property to interface

Copilot · 2026-01-20T09:59:29Z

DevProxy/Proxy/ProxyConfiguration.cs

    public string? IPAddress { get; set; } = "127.0.0.1";
    public bool InstallCert { get; set; } = true;
    [JsonConverter(typeof(JsonStringEnumConverter))]
+    public LogFor LogFor { get; set; } = LogFor.Human;


The LogFor property in ProxyConfiguration is settable (public setter), but in IProxyConfiguration it's defined as read-only (only a getter). This inconsistency could lead to issues where the configuration can be changed through ProxyConfiguration but not through the interface contract. Consider making LogFor read-only in ProxyConfiguration by removing the set accessor, or if it needs to be settable, add a setter to the IProxyConfiguration interface.

Copilot · 2026-01-20T09:59:30Z

DevProxy/Logging/ProxyConsoleFormatterOptions.cs

+using DevProxy.Abstractions.Proxy;
 using Microsoft.Extensions.Logging.Console;

 namespace DevProxy.Logging;

 sealed class ProxyConsoleFormatterOptions : ConsoleFormatterOptions
 {
+    public LogFor LogFor { get; set; } = LogFor.Human;
+


The ProxyConsoleFormatterOptions class has a LogFor property that is set but never used in the ProxyConsoleFormatter class. This suggests that the LogFor property may be unnecessary in ProxyConsoleFormatterOptions, or the ProxyConsoleFormatter should be using it. Given that the machine mode is selected by choosing a different formatter (MachineConsoleFormatter), this property appears to be dead code in the context of ProxyConsoleFormatter.

Suggested change

using DevProxy.Abstractions.Proxy;

using Microsoft.Extensions.Logging.Console;

namespace DevProxy.Logging;

sealed class ProxyConsoleFormatterOptions : ConsoleFormatterOptions

{

public LogFor LogFor { get; set; } = LogFor.Human;

using Microsoft.Extensions.Logging.Console;

namespace DevProxy.Logging;

sealed class ProxyConsoleFormatterOptions : ConsoleFormatterOptions

{

Initial plan

60d59af

Copilot AI assigned Copilot and waldekmastykarz Jan 19, 2026

Copilot started work on behalf of waldekmastykarz January 19, 2026 11:55 View session

Copilot AI and others added 2 commits January 19, 2026 12:06

Add --log-for human|machine flag for LLM/agent-friendly output

4f38ff5

Co-authored-by: waldekmastykarz <11164679+waldekmastykarz@users.noreply.github.com>

Fix code review feedback: add token count check and remove unnecessar…

4b00ab7

…y else Co-authored-by: waldekmastykarz <11164679+waldekmastykarz@users.noreply.github.com>

Copilot AI changed the title ~~[WIP] Add --log-for human|machine flag for LLM/agent-friendly output~~ Add --log-for human|machine flag for LLM/agent-friendly output Jan 19, 2026

Copilot AI requested a review from waldekmastykarz January 19, 2026 12:12

Copilot finished work on behalf of waldekmastykarz January 19, 2026 12:12

Merge branch 'main' into copilot/add-log-for-flag

1859143

waldekmastykarz marked this pull request as ready for review January 20, 2026 09:55

waldekmastykarz requested a review from a team as a code owner January 20, 2026 09:55

Copilot AI review requested due to automatic review settings January 20, 2026 09:55

Copilot started reviewing on behalf of waldekmastykarz January 20, 2026 09:55 View session

Copilot started work on behalf of waldekmastykarz January 20, 2026 09:56 View session

Copilot AI reviewed Jan 20, 2026

View reviewed changes

Copilot finished work on behalf of waldekmastykarz January 20, 2026 10:00

garrytrinder self-assigned this Jan 20, 2026

Provide feedback

Saved searches

Use saved searches to filter your results more quickly

Uh oh!

Add --log-for human|machine flag for LLM/agent-friendly output #1508

Add --log-for human|machine flag for LLM/agent-friendly output #1508

Uh oh!

Copilot AI commented Jan 19, 2026 •

edited

Loading

Uh oh!

waldekmastykarz commented Jan 20, 2026

Uh oh!

Copilot AI commented Jan 20, 2026 •

edited

Loading

I tried to connect to the following addresses, but was blocked by firewall rules:

Uh oh!

Copilot AI left a comment

Uh oh!

Copilot AI Jan 20, 2026

Uh oh!

Copilot AI Jan 20, 2026

Uh oh!

Reviewers

Assignees

Labels

Projects

Milestone

Development

Uh oh!

3 participants

Problem	Description
ANSI escape codes	Color codes like `\x1B[31m` pollute text and waste tokens
Unicode box characters	`╭ ╰ │` are visual, not semantic — hard to parse programmatically
No structured output	Console is human-readable prose; LLMs need JSON to reliably extract fields
Buffered output	Messages held until request completes; agents cannot react in real-time
Terse/informal labels	`oops`, `skip`, `proc` are cute but ambiguous for machines
Missing context	Logs like "URL not matched" lack the actual URL
No correlation IDs	Hard to trace request→response chains
Timestamps hidden	Filtered by default; agents cannot measure timing

Tool	Flag
kubectl	`-o, --output json\|yaml\|wide`
Azure CLI	`-o, --output json\|table\|tsv`
GitHub CLI	`--json`

Aspect	`--log-format json`	`--log-for machine`
Semantics	Describes the how	Describes the who
LLM intuition	"Output in JSON format"	"This output is meant for me"
Discoverability	Need to know JSON is the right format	Obvious: "I am a machine, I use `machine`"
Future-proof	Locked to specific format	Can evolve what "machine" means internally

Add --log-for human|machine flag for LLM/agent-friendly output #1508

Are you sure you want to change the base?

Add --log-for human|machine flag for LLM/agent-friendly output #1508

Uh oh!

Conversation

Copilot AI commented Jan 19, 2026 • edited Loading Uh oh! There was an error while loading. Please reload this page.

Uh oh!

Changes

Usage

Output

I tried to connect to the following addresses, but was blocked by firewall rules:

Problem

Example of current output

What an agent needs

Proposed solution

Why --log-for instead of --output json or --format json?

Machine output requirements

Configuration

Related

Comments on the Issue (you are @copilot in this section)

Uh oh!

waldekmastykarz commented Jan 20, 2026

Uh oh!

Copilot AI commented Jan 20, 2026 • edited Loading Uh oh! There was an error while loading. Please reload this page.

Uh oh!

I tried to connect to the following addresses, but was blocked by firewall rules:

Uh oh!

Copilot AI left a comment

Choose a reason for hiding this comment

Pull request overview

Reviewed changes

Uh oh!

Copilot AI Jan 20, 2026

Choose a reason for hiding this comment

Uh oh!

Copilot AI Jan 20, 2026

Choose a reason for hiding this comment

Uh oh!

Reviewers

Assignees

Labels

Projects

Milestone

Development

Uh oh!

3 participants

Copilot AI commented Jan 19, 2026 •

edited

Loading

Why `--log-for` instead of `--output json` or `--format json`?

Copilot AI commented Jan 20, 2026 •

edited

Loading