Add support for YAML-based config by Copilot · Pull Request #1491 · dotnet/dev-proxy

Copilot · 2026-01-13T13:14:44Z

Adds YAML as an alternative to JSON for all configuration files. Supports YAML anchors and merge keys for reusable configuration blocks.

New Files

DevProxy.Abstractions/Utils/ProxyYaml.cs - YAML-to-JSON conversion with anchor/alias/merge key support
DevProxy.Abstractions/Extensions/YamlConfigurationExtensions.cs - ASP.NET Core IConfigurationProvider for YAML files
DevProxy/devproxyrc.yaml - YAML version of default configuration (reference example)
DevProxy/devproxy-errors.yaml - YAML version of default error responses (reference example demonstrating anchors)

Modified Files

ConfigurationManagerExtensions.cs - Added devproxyrc.yaml/.yml to config file discovery
BaseLoader.cs - Convert YAML plugin configs to JSON before processing
ConfigCommand.cs - Detect YAML config/mock files in downloaded samples
DevProxy.csproj - Include YAML config files in build output and installer

Features

.yaml and .yml extensions supported everywhere JSON is used
YAML 1.1 boolean values (yes/no, on/off, true/false)
Full anchor/alias support with merge key precedence (explicit values override merged)

Example

definitions:
  throttled: &throttled
    statusCode: 429
    body: '{"error": "Too many requests"}'

mocks:
  - request:
      url: https://graph.microsoft.com/v1.0/users
    response:
      <<: *throttled
  - request:
      url: https://graph.microsoft.com/v1.0/groups
    response:
      <<: *throttled

Backward compatible—existing JSON configuration continues to work unchanged.

Original prompt

This section details on the original issue you should resolve

<issue_title>Add support for YAML-based config</issue_title>
<issue_description>Support both JSON- and YAML-based config.

YAML would be particularly beneficial for including comments (although they are supported in JSONC, but that's not always obvious) and multiline strings (ie. mocks).

One more thing that would be beneficial are anchors for repeated patterns:
definitions:
  throttled: &throttled
    statusCode: 429
    body: '{"error": "Too many requests"}'

responses:
  - url: https://graph.microsoft.com/v1.0/users
    <<: *throttled
  - url: https://graph.microsoft.com/v1.0/groups
    <<: *throttled
Notice how for both responses we reuse the same definition, significantly simplifying the config.

YAML config should be supported everywhere where we allow JSON-based config (root, plugins, etc)</issue_description>

Comments on the Issue (you are @copilot in this section)
@garrytrinder Nice idea! Let's do it 💪

Fixes Add support for YAML-based config #1489

💬 We'd love your input! Share your thoughts on Copilot coding agent in our 2 minute survey.

waldekmastykarz

@copilot have you also considered supporting YAML in config files for plugins, like mocks, CRUD API, etc?

Copilot · 2026-01-14T11:46:44Z

@copilot have you also considered supporting YAML in config files for plugins, like mocks, CRUD API, etc?

Yes, YAML is already supported for all plugin config files. The BaseLoader class (which all loaders like MockResponsesLoader, CrudApiDefinitionLoader, etc. inherit from) automatically detects .yaml/.yml files and converts them to JSON before processing.

Users can specify YAML files for mocks, CRUD API definitions, error responses, rate limiting configs, and all other plugin-specific configuration files - they just need to use the .yaml or .yml extension.

waldekmastykarz

@copilot

DevProxy.Abstractions/Plugins/BaseLoader.cs

Copilot

Pull request overview

Adds first-class YAML support for Dev Proxy configuration files so users can author configs in either JSON/JSONC or YAML (including anchors and merge keys), while keeping existing JSON configs working.

Changes:

Added a YAML-to-JSON conversion utility (ProxyYaml) and a YAML IConfigurationProvider for loading root config from .yaml/.yml.
Updated config file discovery/loading to recognize devproxyrc.yaml/.yml and route through a new AddConfigFile helper.
Updated sample config/mock detection to include YAML files when scanning downloaded config folders.

Reviewed changes

Copilot reviewed 5 out of 5 changed files in this pull request and generated 3 comments.

Show a summary per file

File	Description
DevProxy/Extensions/ConfigurationManagerExtensions.cs	Adds `.yaml/.yml` to devproxyrc discovery and uses `AddConfigFile` for JSON/YAML loading.
DevProxy/Commands/ConfigCommand.cs	Expands sample config/mock detection to include YAML files.
DevProxy.Abstractions/Utils/ProxyYaml.cs	Introduces YAML-to-JSON conversion with merge-key handling and scalar typing.
DevProxy.Abstractions/Plugins/BaseLoader.cs	Converts YAML plugin/mock files to JSON before schema validation and parsing.
DevProxy.Abstractions/Extensions/YamlConfigurationExtensions.cs	Adds YAML configuration source/provider and `AddConfigFile` extension method.

DevProxy.Abstractions/Extensions/YamlConfigurationExtensions.cs

DevProxy.Abstractions/Utils/ProxyYaml.cs

DevProxy.Abstractions/Extensions/YamlConfigurationExtensions.cs

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

… normalization - Handle nested merge keys recursively in CollectMergedValues instead of skipping them - Distinguish quoted empty strings from null using ScalarStyle in ProxyYaml - Normalize YAML 1.1 booleans (yes/no/on/off) to true/false in YamlConfigurationProvider

garrytrinder

Should we include an example default YAML configuration file alongside the existing devproxyrc.json file?

waldekmastykarz · 2026-02-23T15:13:43Z

Should we include an example default YAML configuration file alongside the existing devproxyrc.json file?

Good idea. It wouldn't be used, but it would be a good reference for folks.

waldekmastykarz · 2026-02-23T15:15:09Z

Should we include an example default YAML configuration file alongside the existing devproxyrc.json file?

Good idea. It wouldn't be used, but it would be a good reference for folks.

@copilot Add a YAML version of the default configuration (https://github.com/dotnet/dev-proxy/blob/main/DevProxy/devproxyrc.json and https://github.com/dotnet/dev-proxy/blob/main/DevProxy/devproxy-errors.json). Ensure, that both files are copied to the output on building and included in the installer.

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

Copilot · 2026-02-23T15:18:47Z

Should we include an example default YAML configuration file alongside the existing devproxyrc.json file?

Good idea. It wouldn't be used, but it would be a good reference for folks.
...

Added in c02bc37:

devproxyrc.yaml - YAML version of the default config
devproxy-errors.yaml - YAML version of error responses (demonstrates YAML anchors)

Both files are copied to output on build and will be included in the installer automatically (since the installer copies all files from the build output directory).

garrytrinder

We've got some issues with validation for files and plugins in YAML.

garrytrinder · 2026-02-23T16:46:31Z

DevProxy/devproxy-errors.yaml

+# It demonstrates YAML features like comments, multiline strings, and anchors.
+
+# Define reusable error body templates using YAML anchors
+definitions:


This results in an diagnostic error in VS Code when a YAML language server is present.

garrytrinder · 2026-02-23T16:47:17Z

DevProxy/devproxyrc.yaml

Schema validation is skipped for both the config file and plugin.

Copilot AI assigned Copilot and waldekmastykarz Jan 13, 2026

Copilot started work on behalf of waldekmastykarz January 13, 2026 13:15 View session

Copilot AI changed the title ~~[WIP] Add support for YAML-based configuration~~ Add support for YAML-based config Jan 13, 2026

Copilot AI requested a review from waldekmastykarz January 13, 2026 13:40

Copilot finished work on behalf of waldekmastykarz January 13, 2026 13:40

waldekmastykarz requested changes Jan 14, 2026

View reviewed changes

Copilot started work on behalf of waldekmastykarz January 14, 2026 11:45 View session

waldekmastykarz reviewed Jan 14, 2026

View reviewed changes

DevProxy.Abstractions/Plugins/BaseLoader.cs Show resolved Hide resolved

Copilot AI requested a review from waldekmastykarz January 14, 2026 11:47

Copilot finished work on behalf of waldekmastykarz January 14, 2026 11:47

Copilot started work on behalf of waldekmastykarz January 14, 2026 11:47 View session

Copilot finished work on behalf of waldekmastykarz January 14, 2026 11:49

waldekmastykarz marked this pull request as ready for review February 22, 2026 10:22

waldekmastykarz requested a review from a team as a code owner February 22, 2026 10:22

Copilot AI review requested due to automatic review settings February 22, 2026 10:22

Copilot started reviewing on behalf of waldekmastykarz February 22, 2026 10:23 View session

Copilot AI reviewed Feb 22, 2026

View reviewed changes

DevProxy.Abstractions/Extensions/YamlConfigurationExtensions.cs Outdated Show resolved Hide resolved

DevProxy.Abstractions/Utils/ProxyYaml.cs Show resolved Hide resolved

DevProxy.Abstractions/Extensions/YamlConfigurationExtensions.cs Outdated Show resolved Hide resolved

Copilot AI and others added 6 commits February 22, 2026 13:45

Initial plan

1f26e0f

Add YAML configuration support with anchors and merge keys

05c08c4

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

Fix YAML merge key precedence logic

d9bc12d

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

Fix unsafe casts in YAML processing

11f91aa

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

Improve YAML boolean and null value detection per YAML spec

5d6ace8

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

waldekmastykarz force-pushed the copilot/add-yaml-config-support branch from 66b37c6 to a0204d8 Compare February 22, 2026 12:45

Merge branch 'main' into copilot/add-yaml-config-support

eaaa42f

garrytrinder reviewed Feb 23, 2026

View reviewed changes

Copilot started work on behalf of waldekmastykarz February 23, 2026 15:15 View session

Add YAML versions of default configuration files

c02bc37

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

Copilot finished work on behalf of waldekmastykarz February 23, 2026 15:19

garrytrinder requested changes Feb 23, 2026

View reviewed changes

Merge branch 'main' into copilot/add-yaml-config-support

503f8aa

garrytrinder marked this pull request as draft February 23, 2026 17:05

Comments

Conversation

Copilot AI commented Jan 13, 2026 • edited Loading Uh oh! There was an error while loading. Please reload this page.

Uh oh!

New Files

Modified Files

Features

Example

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

Uh oh!

waldekmastykarz left a comment

Choose a reason for hiding this comment

Uh oh!

Copilot AI commented Jan 14, 2026

Uh oh!

waldekmastykarz left a comment

Choose a reason for hiding this comment

Uh oh!

Uh oh!

Copilot AI left a comment

Choose a reason for hiding this comment

Pull request overview

Reviewed changes

Uh oh!

Uh oh!

Uh oh!

Uh oh!

garrytrinder left a comment

Choose a reason for hiding this comment

Uh oh!

waldekmastykarz commented Feb 23, 2026

Uh oh!

waldekmastykarz commented Feb 23, 2026

Uh oh!

Copilot AI commented Feb 23, 2026

Uh oh!

garrytrinder left a comment

Choose a reason for hiding this comment

Uh oh!

garrytrinder Feb 23, 2026

Choose a reason for hiding this comment

Uh oh!

garrytrinder Feb 23, 2026

Choose a reason for hiding this comment

Uh oh!

Reviewers

Assignees

Labels

Projects

Milestone

Development

Uh oh!

3 participants

Copilot AI commented Jan 13, 2026 •

edited

Loading