docs: add tutorial for creating custom CTRF attestation type

Author: sofusalbertsen

docs.kosli.com/content/tutorials/custom-attestation-ctrf.md

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+---
+title: "Creating custom CTRF attestation type"
+bookCollapseSection: false
+weight: 508
+summary: "In this tutorial, we will create a custom attestation type with schema and evaluation for Common Test Report Format"
+---
+
+## Custom Attestations
+
+Custom attestations in Kosli allow you to report and verify any type of data as part of your software delivery process. When defining a custom attestation type, you provide two powerful mechanisms to ensure data integrity and compliance:
+
+1. **Schema**: A [JSON schema](https://json-schema.org/learn) that validates the format of the data being reported. This ensures that the input strictly adheres to the expected structure, preventing malformed data from entering your system.
+2. **JQ Rule**: A [jq](https://jqlang.github.io/jq/) expression used to evaluate the data against your compliance policies. This rule determines whether the reported data passes or fails your requirements (e.g., "zero failed tests").
+
+## Common Test Report Format (CTRF)
+
+The [Common Test Report Format (CTRF)](https://ctrf.io/) is a standardized JSON schema for test execution reports. It solves the problem of fragmented test output formats by providing a universal structure, regardless of the testing framework (Jest, Pytest, Mocha, etc.) or language used.
+
+Adopting a common format like CTRF significantly simplifies compliance evaluation. Instead of writing unique parsing logic and compliance rules for every testing tool in your stack, you can define a single Kosli attestation type for CTRF. This allows you to uniformly enforce quality gates—such as "no failed tests"—across all your projects.
+
+## Creating the Custom Type
+
+To start reporting CTRF results to Kosli, you first need to create a custom attestation type. We will name it `ctrf`.
+
+### 1. Define the Schema
+
+First, ensure you have a JSON schema that matches the CTRF specification. This schema will be used to validate that the reports sent to Kosli are valid CTRF reports.
+
+Download the [official schema](https://ctrf.io/docs/full-schema) to a file named `ctrf-schema.json` with the necessary validation structure.
+
+### 2. Create the Type via CLI
+
+Use the `kosli create attestation-type` command to define the new type. We will add a jq rule to ensure that the number of failed tests in the summary is zero.
+
+```shell
+kosli create attestation-type ctrf \
+  --description "Attestation for Common Test Report Format (CTRF)" \
+  --schema ctrf-schema.json \
+  --jq '.results.summary.failed == 0'
+```
+
+In this command:
+
+* `--schema ctrf-schema.json`: Points to the JSON schema file for validation.
+* `--jq '.results.summary.failed == 0'`: Sets the compliance rule. The attestation will only pass if the `failed` count in the report summary is exactly 0.
+
+### 3. Report the Attestation
+
+Once your tests have run and generated a CTRF report (e.g., `ctrf-report.json`), you can report it to Kosli using the `kosli attest custom` command.
+
+```shell
+kosli attest custom \
+  --type ctrf \
+  --name playwright-tests \
+  --attestation-data ctrf-report.json
+```
+
+In this command:
+
+* `--name playwright-tests`: A name for this specific attestation instance (e.g., identifying the test suite).
+* `--attestation-data ctrf-report.json`: The path to the actual CTRF report file generated by your test runner.
+* `--type ctrf`: Specifies the custom attestation type we created earlier.
+
+Kosli will validate `ctrf-report.json` against the schema and evaluate the jq rule. If the report is valid and `.results.summary.failed` is 0, the attestation will be marked as compliant.
+
+Resources:
+
+* [create custom attestation type](/client_reference/kosli_create_attestation-type)
+* [report custom attestation to an artifact or a trail](/client_reference/kosli_attest_custom/) for usage details and examples.
+* [Naming convention for attestation types in Kosli](/implementation_guide/phase_2/plan_organizational_structure/naming_conventions/attestation_types/)